30. 3.1.10.1. Temperature and duration of washing and dry cycles ⦠..... 45 The relation between fabric Thickness, Density and Heat Transfer â¦. 147.
Ain Shams University Women’s College for Arts, Science & Education Home Economics Department
Thesis Submitted for Requirements of M.Sc. (Home Economics-Textile and Clothing)
Entitled Manufacturing & Study of Protective Clothing Specifications and its Wearing Applications in Different Fields
By HEBA ZAKARIA MOHAMED ABOU HASHISH
Supervised By Prof. Dr. Wafaa A. Elsayed Prof of Applied Textile Chemistry, Head of Home Economics Dept., Dean of Women’s College, Ain Shams University
Prof. Dr. Mohamed A. Saad Prof & Head of Textile Engineering Dept., The National Research Center
Dr. Eng. Mamdouh Y. Sharkas Lecturer of Weaving Tech. Women’s College – Ain Shams University
2008
Ain Shams University Women’s College for Arts, Science & Education Home Economics Department
Thesis Submitted for Requirements of M.Sc. (Home Economics-Textile and Clothing)
Manufacturing & Study of Protective Clothing Specifications and its Wearing Applications in Different Fields By
HEBA ZAKARIA M. ABOU HASHISH Supervised By Prof. Dr. Wafaa A. Elsayed Prof of Applied Textile Chemistry, Head of Home Economics Dept., Dean of Women’s College, Ain Shams University
Prof. Dr. Mohamed A. Saad Prof & Head of Textile Engineering Dept., The National Research Center
Dr. Eng. Mamdouh Y. Sharkas Lecturer of Weaving Tech. Women’s College – Ain Shams University
2008
Ain Shams University Women’s College for Arts, Science & Education Home Economics Department
Thesis Submitted for Requirements of M.Sc. (Home Economics-Textile and Clothing)
Entitled Manufacturing & Study of Protective Clothing Specifications and its Wearing Applications in Different Fields
By HEBA ZAKARIA MOHAMED ABOU HASHISH
Supervised By Prof. Dr. Wafaa A. Elsayed Prof of Applied Textile Chemistry, Head of Home Economics Dept., Dean of Women’s College, Ain Shams University
Prof. Dr. Mohamed A. Saad Prof & Head of Textile Engineering Dept., The National Research Center
Dr. Eng. Mamdouh Y. Sharkas Lecturer of Weaving Tech. Women’s College – Ain Shams University
2008
﴿ﻭ ﹸﻗ ﹾﻞ ﺭﺏ ﺍ ﺭﺣ ﻤ ﻬﻤﺎ ﻛﹶﻤﺎ ﺭﺑﻴﺎﻧﹺﻲ ﺻﻐﻴﺮﺍ﴾ ﺻﺪﻕ ﺍﷲ ﺍﻟﻌﻈﻴﻢ
Special Dedication
For my Father For my Mother Sending you my Love
ACKNOWLEDGMENTS I would like to express my gratitude to my advisor and mentor
Prof.Dr. Mohamed Saad for giving me the opportunity to work with him and for his invaluable guidance, support, encouragement and time that he spent with me throughout my study which made it a great learning experience. I would like to extend my appreciation to Prof.Dr. Wafaa Anwar for her support and experiences she gave to me. I would like to thank Dr.Eng. Mamdouh Sharkas for his advises and encouragements during this study. Last, but certainly not least I would like to thank My Parents. Without their love, support and encouragements this work would not have been possible.
Thank you all.
CONTENTS Title
Page
List of Figures ……………………………………………………………………………………………
VI
List of Tables …………………………………………………………………………………………….
VIII
List of Products ………………………………………………………………………………………….
IX
Summary ………………………………………………………………………………….
і
Part 1: Introduction and Literature Review Chapter 1: Introduction ………………………………………………………………………
1
Chapter 2: Background …………………………………………………………………………
9
2.1.
The Importance of Nonwovens in Technical Textile Applications ………
9
2.2.
History of Nonwoven Technology ……………………………………………………
12
2.3.
Applications and user Industries ……………………………………………………..
13
Chapter 3: High Performance & High Temperature Resistant Fibers
15
3.1.
Meta aramide: Nomex (DuPont) …………………………………………………….. 3.1.1 3.1.2.
What is Nomex? ……………………………………………………………..
21 21
Development And Molecular Structure Of Nomex Brand Fiber ………………………………………………………………………………
24
3.1.3.
Durability And Cost Effectiveness …………………………………….
25
3.1.4.
Lightweight Comfort ……………………………………………………….
25
3.1.5.
Professional Appearance ………………………………………………….
25
3.1.6.
Easy Care ……………………………………………………………………….
26
3.1.7.
Fiber Properties ………………………………………………………………
26
3.1.8.
Flammability, Smoke And Off-Gas Generation ………………….
28
3.1.9.
Resistance To Degradation ………………………………………………
29
3.1.10.
Some Guidance About Washing And Drying Of Nomex Garments ………………………………………………………………………. 3.1.10.1.
30
Temperature and duration of washing and dry cycles ……………………………………………………………
30
3.1.10.2.
PH of Soaps and Detergents ……………………….....
30
3.1.10.3.
Appearance …………………………………………………..
31
I
3.1.10.4. 3.2.
3.3.
Cost Effectiveness ………………………………………….
Polyimide (PI): P84 ………………………………………………………………………
31 32
3.2.1.
Fiber Properties ………………………………………………………………
33
3.2.2.
Cross section of P84 Fibers ………………………………………………
34
3.2.3.
The Thermal Properties …………………………………………………..
35
3.2.4.
Applications ……………………………………………………………………
38
3.2.5.
Sealing Applications ………………………………………………………..
40
3.2.6.
Protective Clothing ………………………………………………………….
40
Glass Fiber ……………………………………………………………………...................
42
3.3.1.
Fiber Types & Composition ………………………………………………
47
3.3.2.
Formation ………………………………………………………………………
48
3.3.3.
Chemistry ………………………………………………………………………
49
3.3.4.
Molecular Structure of Glass ……………………………………………
50
3.3.5.
Manufacturing Processes …………………………………………………
51
3.3.6.
Fiber Structure ……………………………………………………………….
56
3.3.7.
Properties ………………………………………………………………………
57
3.3.8.
Uses & Applications ………………………………………………………..
62
Chapter 4: Nonwovens …………………………………………………………………………
65
4.1.
Needle Punched Nonwovens ………………………………………………………….. 4.1.1.
Process …………………………………………………………………………..
67
4.1.2.
The Felting Needle ………………………………………………………….
67
4.1.3.
Finishing of Nonwovens ………………………………………………….
71
4.1.3.1.
Mechanical ……………………………………………………
71
4.1.3.2.
Chemical ………………………………………………………
72
Printing Nonwovens ………………………………………………………..
73
4.1.4.1.
Printing of light weight Nonwovens ………………..
74
4.1.4.2.
Printing of Heavy Nonwovens ………………………..
76
4.1.4.3.
Spray Printing ……………………………………………….
78
4.1.4.4.
Transfer Printing …………………………………………..
78
Classification Of Nonwovens …………………………………………………………..
80
4.1.4.
4.2.
67
4.2.1.
Classification based on web formation ………………………………
80
4.2.2.
Classification based on web consolidation …………………………
81
4.2.3.
Classification based on fiber type ……………………………………..
81
II
4.3.
Characteristics & Properties of Nonwovens ………………………………………
82
4.4.
Uses of Nonwovens ………………………………………………………………………..
83
Chapter 5: High Performance Composites …………………………………………
85
5.1.
Composites ……………………………………………………………………………………
86
5.2.
Fabric Lamination …………………………………………………………………………
87
5.3.
Mechanical and impact properties of needle punched nonwoven composites …………………………………………………………………………………….
89
Scrims …………………………………………………………………………………………..
90
5.4.1.
Scrims reinforce nonwovens …………………………………………….
91
5.4.2.
Advantages of scrims ………………………………………………………
91
Chapter 6: Comfort Properties of Heat-Resistant Protective Wear …
93
5.4.
Part 2: Aim of the Work Part 3: Experimental Work Chapter 7: Experimental Work …………………………………………………………… 7.1.
7.2.
7.3.
99
Materials ………………………………………………………………………………………
99
7.1.1.
Nomex …………………………………………………………………………..
102
7.1.2.
Polyimide (P84) ……………………………………………………………..
102
7.1.3.
Glass Fiber ……………………………………………………………………..
103
Experimental Tests ………………………………………………………………………..
103
7.2.1.
Fabric Thickness …………………………………………………………….
103
7.2.2.
Fabric Weight …………………………………………………………………
104
7.2.3.
Fabric Density ………………………………………………………………..
104
7.2.4.
Breaking Strength …………………………………………………………..
104
7.2.5.
Elongation ……………………………………………………………………..
105
7.2.6.
Air Permeability ……………………………………………………………..
105
7.2.7.
Tearing Strength …………………………………………………………….
105
7.2.8.
Drapeability ……………………………………………………………………
106
7.2.9.
Fabric Stiffness ……………………………………………………………….
106
7.2.10.
Surface Roughness ………………………………………………………….
106
7.2.11.
Water Repellency ……………………………………………………………
106
7.2.12.
Heat Transfer …………………………………………………………………
107
Sewing Techniques ………………………………………………………………………..
107
III
7.3.1.
Thread …………………………………………………………………………..
108
7.3.2.
Stitch type ………………………………………………………………………
108
7.3.3.
Seam construction …………………………………………………………..
109
7.3.4.
Needles ………………………………………………………………………….
111
7.3.5.
Sewing machine ……………………………………………………………..
111
7.3.6.
Radar Chart ……………………………………………………………………
111
Printing ………………………………………………………………………………………..
112
Chapter 8: Results & Discussion ……………………………………………………….…
119
7.4. 8.1.
Results ………………………………………………………………………………………….
119
8.2.
Patterns and layout ………………………………………………………………………..
123
8.2.1.
Pattern No. 1 …………………………………………………………………..
123
8.2.2.
Pattern No. 2 ………………………………………………………………….
124
8.2.3.
Pattern No. 3 ………………………………………………………………….
125
8.2.4.
Pattern No. 4 ………………………………………………………………….
126
8.2.5.
Pattern No. 5 ………………………………………………………………….
127
8.2.6.
Pattern No. 6 ………………………………………………………………….
128
8.2.7.
Pattern No. 7 …………………………………………………………………..
129
8.2.8.
Pattern No. 8 ………………………………………………………………….
130
8.2.9.
Pattern No. 9 ………………………………………………………………….
131
8.2.10.
Pattern No. 10 …………………………………………………………………
132
8.2.11.
Pattern No. 11 …………………………………………………………………
133
8.2.12.
Pattern No. 12 …………………………………………………………………
134
8.2.13.
Pattern No. 13 …………………………………………………………………
135
8.2.14.
Pattern No. 14 …………………………………………………………………
136
8.2.15.
Pattern No. 15 …………………………………………………………………
137
8.2.16.
Pattern No. 16 …………………………………………………………………
138
8.2.17.
Pattern No. 17 …………………………………………………………………
139
Silkscreen Patterns ………………………………………………………………………..
140
8.3.1.
Silkscreen pattern for Model No. 1 ……………………………………
140
8.3.2.
Silkscreen pattern for Model No. 3 ……………………………………
141
8.3.3.
Silkscreen pattern for Model No. 4 ……………………………………
142
8.3.4.
Silkscreen pattern for Model No. 5 ……………………………………
143
8.3.5.
Silkscreen pattern for Model No. 6 ……………………………………
144
8.3.6.
Silkscreen pattern for Model No. 7 ……………………………………
145
8.3.
IV
8.3.7. 8.4.
Silkscreen pattern for Model No. 8 ……………………………………
146
Results Discussion …………………………………………………………………………
147
Part 4: Products Chapter 9: Products ……………………………………………………………………………
154
Kitchen Sets Model No. 1 …………………………………………………………………………………..
154
Model No. 2 …………………………………………………………………………………..
156
Model No. 3 …………………………………………………………………………………..
158
Model No. 4 …………………………………………………………………………………..
160
Model No. 5 …………………………………………………………………………………..
162
Model No. 6 …………………………………………………………………………………..
164
Model No. 7 …………………………………………………………………………………..
166
Model No. 8 …………………………………………………………………………………..
168
Steel Workers Model No. 9 ………………………………………………………………………………….
169
Model No. 10 …………………………………………………………………………………
170
Model No. 11 ………………………………………………………………………………….
171
Model No. 12 …………………………………………………………………………………
172
Firefighters Model No. 13 …………………………………………………………………………………
173
Model No. 14 …………………………………………………………………………………
174
Model No. 15 …………………………………………………………………………………
175
Welders Model No. 16 …………………………………………………………………………………
176
Model No. 17 …………………………………………………………………………………
177
Recommendations ……………………………………………………………………………………..
178
References ………………………………………………………………………………………………..
179
Arabic Summary
V
List of Figures Figure No. 1
Figure Name
Page No.
Distribution of world technical textile consumption according to protection applications ………………………………………………………………..
10
2
The technical and nonwoven textile production streams …………………
12
3
NOMEX® meta-aramid [poly (meta-phenyleneisophthalamide)] ……
24
4
Photomicrograph of a Typical Cross Section of Nomex …………………..
26
5
P84 Chemical Structure ……………………………………………………………….
33
6
Monomers used for manufacturing of P84 polymer ………………………..
34
7
P84 Fibers Cross Section ……………………………………………………………..
35
8
Short Term Temperature Stability of P84 ………………………………………
36
9
Isothermal thermo gravimetric analysis of p84 fibers ……………………..
36
10
Limiting Oxygen Index (LOI) of Fibers ………………………………………….
37
11
P84 fiber shrinkage characteristics duration: ………….……………………..
38
12
Fiberglass continuous filaments …………………………..……………………….
44
13
Schematic of glass fiber fabric weaves …………………………………………..
45
14
Fiberglass staple fiber can be twisted and plied into yarns ………………
46
15
Glass Tetra …………………………………………………………………………………
49
16
Schematic diagram of a two-stage process for the production of continuous filament fiber glass …………………………………………………….
17
55
Schematic diagrams of one-stage, direct-melt processes for the production of continuous filament fiber glass ………………………………..
55
18
Glass fiber resembles smooth glass rods of very small diameter ………
59
19
Hollow S-2 Fiberglass ………………………………………………………………….
59
20
Fiberglass vs. Wool and human hair……………………………………………..
61
21
Impact strengths of various high-performance fibers ……………………..
62
22
Photograph of differing forms of glass fibers as reinforcement ………..
63
23
Mechanical Bonding ……………………………………………………………………
67
24
Types of Needles …………………………………………………………………………
68
VI
List of Figures 25
Felting Needles …………………………………………………………………………..
69
26
Needle action ……………………………………………………………………………..
70
27
Needle action – Schematic …………………………………………………………..
70
28
Diagram of a transfer calendar ……………………………………………………..
79
29
Flow Diagram of classification of nonwoven web forming techniques.
80
30
Laminates and composites …………………………………………………………..
86
31
Typical balanced – symmetric laminate ……..…………………………………
87
32
Scrim …………………………………………………………………………………………
90
33
Scrim Nonwoven Laminates …………………………………………………………
91
34
Cross-sectional view of the NWN fabric layers ……………………………….
100
35
Needle punching machine ……………………………………………………………
101
36
Photomicrograph of laminated Nomex fabric ………………………………..
102
37
Photomicrograph of laminated P84 fabric ……………………….…………….
102
38
Photomicrograph of Glass fiber fabric …………………………………………..
103
39
Stitches ………………………………………………………………………………………
109
40
Singer Machine (DDL-5550) ………………………………………………………..
111
41
Coating the screen mesh ………………………………………………………………
115
42
Light exposure to screen ………………………………………………………………
116
43
Pouring color on the screen ………………………………………………………….
118
44
Swiping squeegee over the image ………………………………………………….
118
45
The relation between fabric Thickness, Density and Heat Transfer ….
147
46
The mechanical properties of used fabrics (warp direction) …………….
149
47
The mechanical properties of used fabrics (weft direction) ……………..
149
48
Roughness of used fabrics ……………………………………………………………
150
49
The relation between fabric Drapeability, thickness and density ……..
150
50
The stiffness of used fabrics for warp & weft directions …………………..
151
51
Ranking ……………………………………………………………………………………..
152
VII
List of Tables Table No.
Table Name
Page No.
I.
Industrial Fabric construction ……………………………………………………
4
II.
Some samples of nonwovens in technical textile applications ……….
14
III.
Some of the basic characteristics of commodity & high performance fibers classification ……………………………………………….
16
IV.
Typical properties of meta-aramide fibers …………………………………..
22
V.
Typical Applications for Meta-aramide fabrics …………………………….
23
VI.
Typical Properties of Polyimide (PI); p-84 Fiber ………………………….
32
VII.
Typical applications for p-84 polyimide fabrics …………………………..
33
VIII.
The properties of various glass fibers ………………………………………….
58
IX.
Typical glass applications ………………………………………………………….
64
X.
Novel properties and development chart ……………………………………
89
XI.
Different seam classes ………………………………………………………………
110
XII.
Physicomechanical properties of fabrics under experimentation …..
119
XIII.
Air permeability for printed end products …………………………………..
121
XIV.
Normalized Values ……………………………………………………………………
122
VIII
List of Products Model No.
Product Name
Page No.
1
Blocks Set ………………………………………………..
154
2
Bubbles Set ………………………………………………
156
3
Turkish Coffee Set …………………………………….
158
4
Viola Set …………………………………………………..
160
5
Gerbil Set ………………………………………………...
162
6
Butterfly Set ……………………………………………..
164
7
Vanilla Set ………………………………………………..
166
8
Dreamy Set ………………………………………………
168
9
Wrist Guard ……………………………………………..
169
10
Arm Guard Line ………………………………………..
170
11
Sleeve protector ………………………………………..
171
12
Full Sleeve ………………………………………………..
172
13
High Visibility Safety Vest …………………………
173
14
Stay Cool Vest …………………………………………..
174
15
Hi Visibility Phase Change Cooling Vest ……..
175
16
Split-leg Style Apron I ………………………….……
176
17
Split-leg Style Apron II ………………………………
177
IX
SUMMARY The present thesis aims to study the properties of protective clothing for workers who are subjected to heat and fire risks in their work places to achieve both comfort and safety taking into account that the use of protective clothing comes after ensuring the work environment geometrician and managerial. Chefs in hotel kitchens, workers in ironmasters and welders in their workshops are examples for those people exposed to several levels of heat and fire. To achieve such aim, specific high performance fibers are used to produce suitable woven and nonwoven fabrics with specific industrial methods, and then special models are produced. The research covered the following; 1. The importance of safety in work places specifically for those workers exposed to high heat & fire. Also studying the thermal protective clothes and their importance role in protection to overcome thermal hazards such as heat and flame, also mechanical properties have the same importance to withstand cutting and tearing by sharp edges. 2. Suitable high performance fibers (Nomex, P84 and Glass Fiber) were selected, and then their properties were studied to achieve the aim of this work. These are heat and fire resistant, non-melting or dripping, dimensional stability, air permeability, softness, high drape ability as well as abrasion resistance. i
Summary
3. Conversion of high performance fibers into fabric using nonwoven technology of production to produce technical textiles for technical usage. Technical & Nonwoven textiles are durable; they are about function rather than fashion. Our choice for nonwovens due to its advantages of being cheap, high production speed, smooth surface, dense, dimensional stability, its easy, high speed and easier and shorter production technique in turning fiber to fabric. Also, nonwoven products have very important position in technical textiles market due to its large product range and functionality. 4. Producing nonwoven fabric by means of needle punching mechanical binding. Felting the batt by needles penetration turn the batt denser and stronger that affect the mechanical properties of nonwoven fabrics, and that was the reason for choosing this binding method for our application. 5. Laminated or composite fabric – nonwoven-woven-nonwoven (NWN) – reinforcement fabrics are produced. The upper layer of the compound fabric is nonwoven needle punched, away from the skin and heat set. The lower layer is also nonwoven needle punched, contacting the skin with soft comfortable texture. The middle layer is a woven scrim has a reinforcing role, exhibits good stability in the machine and crosswise directions. 6. Some physico-mechanical tests effectuated to evaluate the product such as thickness, weight, density, breaking strength, elongation, ii
Summary
air permeability, tearing strength, drape ability, stiffness, roughness, water repellency and heat transfer characteristics. We predict small differences in the thermo-mechanical properties among these heat-resistance workwear reinforcement materials. − It was found that none of the tested materials (Nomex, P84) would be thermo physiologically uncomfortable under normal
environmental
conditions
even
with
heavy
workloads. − Air resistance increased with fabric thickness and fabric weight per unit area. Also, printing nonwoven fabrics blocks fabric gaps make it less permeable. − Nonwoven composite fabrics have good thermal insulation depending on their thickness and density. − Nonwoven fabrics have the largest bulk density which exhibited the lowest water repellency and so the highest water absorption capacities. On the other hand, glass fiber shows 50% absorbency to water making it suitable for certain protective clothes that interested with this property beside being heat and flame resistant. − Experiments showed that Nomex composite fabric have the better mechanical properties than P84 composite one. So, it’s very evident that stronger garments can be made with greater
tear
resistant
and
breaking
strength
using
nonwoven composite fabrics. − Surface properties of composite fabric, especially when it comes in contact with skin surface, are soft enough that affect the tactile comfort properties. iii
Summary
− Composite fabric is not as drapable as other fabrics, due to higher thickness and density, but it is enough for some special designs of workwear protective clothing. − Fabric stiffness is affected by fabric weight and fiber density. 7. Results of the sewing techniques; − Study seams and stitches types and standards for sewing such protective clothing. − Choose special needles suitable for thick nonwoven fabrics that penetrate it without tearing. − Use special heavy duty industrial sewing machine. − Use thermal Nomex sewing thread. 8. Design suggested protective clothing for different usage and special protection needs; − 8 Kitchen Sets (for chefs & kitchen workers) − 3 Safety Vests (for firefighters & ironmasters workers) − 2 Split-Legs Aprons (for welders) − Different sleeves lengths for arm and hand protection. 9. Printing special designs prepared by Photoshop CS using specific printing pastes by means of silkscreen method to decorate the product. 10. Calculate the material cost and marker efficiency for the suggested models.
iv
Summary
Key Words: composites,
glass fiber, heat transfer, high
performance fibers, laminated fabrics, mechanical properties, needle punching machine, Nomex, P84 polyimide, printing nonwovens, protective clothing, safety, technical textiles, thermo-mechanical properties.
v
P a rt 1
Introduction
1
Introduction Have you ever known some one burned when their
clothes caught fire? House keeper and workers are subjected to the risk of fires, excessive heat on touch inside kitchen. Clothing fires must be avoided because burn injuries are often sever, disfiguring, and can cause death. Such tragedies do not have to happen. However, you must take responsibility for your own safety. Environmental health and safety is an important issue in almost every industry, and functional protective clothing is required for many professionals, such as firefighters, police officers, medical workers, chemical and biological researchers, environmental health workers, pesticide handlers, and soldiers. These protective garments are expected to provide protection against a variety of environmental hazards at the same time and avoid a negative impact on the performance or appearance of the wearers [38]. The increased demands on the properties of the clothing bring more questions to textile scientists such as the following: What functions should the protective clothing provide for a specific professional? What are the necessary levels of protection that the clothing should possess? With the protective functions included in the clothing, what are the performance and comfort properties that the clothing can maintain? How can dual or multi-protective functions be incorporated in the same clothing system? Which material can provide the best balance between the protective properties and the 1
Introduction and Literature Review
comfort provided? Many of the properties are negatively associated with each other since increased protection will usually reduce the comfort of the garments. Therefore, a fundamental investigation of the relationships between the performance and comfort of functional protective materials in the areas of physical, physiological, and social responses is not only necessary but critical to the development of novel textile technologies and the competitiveness of the textile industry [38]. What is Protective Clothing? Protective clothing is clothing designed to protect either the wearer’s body or other items of clothing from hazards such as, heat, chemicals and infection [76]. In this study we manufactured thermal protective clothing for housekeeper to be use to protect against such risks, e.g.; gloves, aprons, pads etc, by selecting some suitable fibers as, glass fiber, Nomex and Polyimide P84, to produce woven and nonwoven fabrics, and then evaluate the quality of these products by different physicomechanical test. Protective clothing does not mean the same to all people. As in most discussions of technical products, we must first define our subject. While all clothing is protective to some degree, our concern is not with routine needs, such as clothing for warmth, rainwear, or routine work clothing. Our focus is on more sophisticated needs, 2
Introduction
protection in situations where hazards or risks are present that have the potential to be life threatening or pose considerable potential for injury or damage to the person working in and around the hazard. In some cases, such as clean rooms, we may be equally concerned about protecting the product we are working with as well as the worker. So then, our definition involves garments, or textile related products that are worn, that prevent a person (or product) from coming into contact with, and that protects from, and/or reduces the risk of exposure to hostile elements or environments [127]. Textiles for protecting objects serve purposes in property protection such as fireproofing and flame proofing, protection against vandalism (protection against cutting), moisture protection and protection for equipment/structural elements, clean room textiles as well as protection against electrostatic and electromagnetic fields. Protective clothing is required in many workplaces in industry, in public companies and in the armed forces. Demand is also growing in the areas of leisure activities, sports, medicine and clean room technology [127]. Protective clothing made from woven, knitted, and nonwoven fabrics have been designed to suit specific requirements, and performance-evaluation techniques to simulate the work wear conditions have been developed [89,109].
3
Introduction and Literature Review
Table I: Industrial fabric construction/art was reproduced, in part, from the Library of Congress Cataloging-in-Publication Data
According to the statistical market analysis for 1996 in Western Europe, the proportion of nonwovens is more than 50% and they are dominant in the area of particle and chemical protection. An annual growth in volume of 5–6% is predicted for Western Europe up to 2005. The use of nonwovens will increase disproportionately rapidly compared to woven and knitted fabrics. In the developing countries, an annual growth of approximately 10% is assumed. Protective clothing is worn for protection against;
4
Introduction
– mechanical influences – being caught by moving parts – thermal, climatic influences, for example cold, heat, moisture, wind – other damaging environmental influence, for example dusts, gases, hot fumes – electrical energy – heat: flames, sparks, radiant heat, molten masses – chemical substances: acids, alkalis, solvents, fats, oils, solid chemicals and – so forth – micro-organisms – danger from vehicles in the form of high-visibility clothing – contamination by radioactive emissions The different types of protective clothing can protect against one or more influences. The performance specifications, conditions of use, testing and certification of protective clothing come under European Directive 89/686/EEC on the approximation of the laws of the Member States relating to personal protective equipment [6]. Manufacturers and retailers should only offer protective clothing for sale if it conforms to the aforementioned directive and the product is labeled externally with the CE mark. The directive formulates the fundamental requirements for protective equipment with regard to health protection and safety function as well as design and the information obligations of the 5
Introduction and Literature Review
manufacturer. The requirements refer to an ergonomically functional design of the clothing with the highest possible level of protection. In addition, the wearer should be subjected to the lowest possible thermal-physiological stresses. The protective clothing should not itself be a source of additional danger or obstructions under the intended end-use conditions. Test and product standards specify the general requirements for product types. Protection from fire and extreme heat, and the need to work around fire and heat, has long provided a need for protective clothing. The primary concern has been to protect the fireman, those working in primary metal industries with molten metal, and similar areas involving
high
heats
such
as
welding,
foundries,
ceramics
manufacture, etc. Nonwovens are a component of protective clothing systems. They vary in the fibrous materials used and in their textile construction. They used as bulky insulation linings with a protective function against the effects of heat from a radiant heat source, flames or hot objects. The
latest
developments
are
nonwovens
made
from
temperature and flame-resistant fibrous materials with a high protective function against the effects of heat and flames. They protect people and property against thermal risks and are being used increasingly in firefighters’ clothing, welders’ protective clothing, combined fire and chemical protective clothing, on public transport, for example planes, trains, in seating and beds as well as in the public 6
Introduction
and private sector. An increasing number of inherently flameresistant fibrous materials are available for producing such nonwovens. By blending appropriate fibers, the different requirements of the respective end-use sector can be met. Chemical methods are not suitable for reinforcing nonwovens as they reduce the LOI (Limiting Oxygen Index) value. Such webs are usually reinforced mechanically [6].
The development of the high heat resistant fibers such as Nomex, Kevlar, PBI, FR Rayon, Kermel, P84, and pre-oxidized PAN based fibers, among others, as well as better FR finishes for cotton and new blends of fibers have made possible far more effective garments. Many of these fibers were developed as asbestos substitutes for high heat areas. The thermal protection is a starting point for development of many of the new high temperature fibers; new ones are being introduced. DuPont
produces
hydroentangled
spunlace
non-woven
Sontara®, of Nomex and Kevlar which is used extensively in thermal protection. These products are used turnout coats as thermal layers where fire resistance and thermal insulation is needed. Increases in thermal protection per unit of weight can be 50-100% over the same weight woven fabric, due to the bulking and still air insulating characteristics, resulting in equal or higher performance levels at a lower weight. They are also used in fire barriers on aircraft, and similar uses [127]. 7
Introduction and Literature Review
To overcome thermal hazards, heat and flame resistant fibers are used to produce thermal protective clothing. Thermal protective clothing should not ignite, they should remain intact, not shrink, melt, or form brittle chars that may break open and expose the wearer; and they should provide as much insulation against heat as is consistent with not diminishing the wearer’s ability to perform a task [89,109].
Total heat energy from a fire can cause a worker’s clothing to ignite, melt, and break open and severe burns to skin. When human tissue is raised from the normal blood temperature of 36.5˚C to 44˚C, skin burns begin to occur, at a rate that depends on the raised temperature level. For example, at 50˚C, damage to the skin is 100 times faster than at 45˚C, and at 72˚C total destruction of the epidermis occurs almost instantaneously [119,122]. The growing concern regarding health and safety of workers in various sectors of the industry has generated regulations and standards, environmental and engineering controls, as well as tremendous research and development in the area of personal protective equipment. There are a number of different tests used for evaluating thermal characteristics of protective clothing, such as easeof-ignition tests, flammability tests, heat-release-measurement tests, extinguishability
tests,
tests
for
measuring
thermal
isolative
properties of fabrics and thermo-person full scale garment burns [14,119].
8
Background
2
Background
2.1. The Importance of Nonwovens in Technical Textile Applications Nowadays, technical textile develops fast in different fields and gains status, have various definitions. Technical textiles are the textile materials and products which are produced for their technical performance and functional properties, instead of their aesthetic and decorative properties [84]. Other definition says “Technical textiles are materials which are specially designed, and are used to fulfill a certain property by only itself or in a process”. We can briefly define technical textiles as the textile webs which
can
offer
engineering
solutions
in
various
technical
applications, because of having lots of different functions. Technical textiles can be component part of another product (tire cord fabric in tires), can be used in a process to manufacture another product (filtration textiles in food production), or can be used alone to perform one or several specific functions (coated fabrics to cover stadiums). There are different terms used for technical textiles. Industrial textiles, high performance textiles, high technical textiles, nontraditional textile, engineering textiles, and high tech textiles are some of the terms used for technical textiles [2].
9
Introduction and Literature Review
Usage and variety of the Technical textile’s products which may be old as traditional textile’s products, was more developed after the high performance synthetic fiber production became widespread. Protective and safety textiles of the most diverse kinds are classed as technical textiles with a high-tech character. They have a growing market importance. Protective clothing occupies first place among technical textiles in Europe
[96].
It is used to protect people
and/or property. For protection at work, protective textiles are used mainly in personal protective equipment (PPE) in the following areas: – Protective clothing
– Protective footwear
– Protective gloves
– Protection against falling
– Protective headgear
– Protective against drowning
The World consumption and prediction of technical textiles between the years 1995-2010 almost in all developed countries, are 40% of total textile production and consumption. It is thought that this value will increase to 50% and above in couple of years [20]. 350 300 250 200
World Consumption
150 100 50 0 1995
2000
2005
2010
Figure (1): Distribution of world technical textile consumption according to protection applications (x 1000 tones) [122].
10
Background
Technical textiles can be classified according to raw materials usage, production methods or end-use fields
[91].
We can classify the
technical textiles according to production methods as follows: 1. Woven fabrics
4. Composite materials
2. Knitted fabrics
5. Tape, Braid
3. Nonwoven
6. Tufting
Technical and nonwoven textiles and fibers are widely regarded as the most thriving and fast changing sector of the global textile industry. Innovation in new materials, processes and applications is expanding non-traditional end uses for both new and existing textile products. Technical textiles and fibers is a high technology and high value-adding activity. In short, technical and nonwoven textiles are about function rather than fashion [63]. The ratio of the nonwoven products in technical textile manufacturing was 31% at 2000 and it is estimated that this ratio would be 39 % at 2010 [101]. Nonwoven materials are single use or durable fabrics that find applications in a host of different technical textile applications including medical devices, civil engineering and construction, automotive and transport components, hygiene and absorbent products, liquid and gas filtration, packaging and protective clothing [72].
Both synthetic and natural fibers are used in manufacturing
technical and nonwoven textiles. The selection and combinations of fibers used determine the ultimate end product properties, cost and subsequent applications [65,104]. 11
Introduction and Literature Review
Figure (2): The technical and nonwoven textile production streams.
2.2. History of Nonwoven Technology Nonwoven technology is one of the conventional sectors of the “traditional” textile industry and was best known for making felt used in craft products such as stuffed toys, hats and shoe linings, to name a few. Indeed, felted fabrics were around for centuries before weaving and knitting technology were invented. This form of manufacturing has surpassed its humble beginnings and is classified by the American Textile Manufacturers Institute (ATMI) as: “A fabric formed of textile fibers that are held together by mechanical interlocking in a random web or mat, by fusing the case of thermoplastic fibers or by bonding with a cementing agent.” [91]
12
Background
The definition of nonwoven products which have 30% share in whole technical textiles market is; “Unique engineering webs consisting of natural or synthetic fibers or filaments, which are not converted to yarns and attached to each other by various processes”. As we can understand from the definition, nonwoven products are quite different from traditional and other technical textiles [91]. One of the most important advantages of nonwoven products is their low production cost. End product can be produced from raw materials with few steps by the high production speeds
[68, 69].
Nonwoven products find place in so many technical textile applications because of their different functions and advantages.
2.3. Applications and user Industries Whilst they play a much more important role than is commonly acknowledged, technical and nonwoven textiles often go unnoticed as they are produced for functional properties rather than aesthetic or decorative characteristics. They are frequently used in a range of downstream applications in other manufacturing and service industries and, thus not highly visible at the retail level. A non-exhaustive list of end-uses includes aerospace, industrial, marine, military, safety and transport textiles and geotextiles. The industry also shares a number of technologies and has overlapping interests with other materials industries such as glass, plastics, films, membranes, metals, composites and paper [63].
13
Introduction and Literature Review
A synopsis of the major applications for technical textiles is listed below – (Table. II) – in alphabetical order (rather than that of importance). Table II: Some samples of nonwovens in technical textile applications [63]. Applications Agriculture (Agrotech) Building & Construction (Buildtech) Clothing (Clothtech) Environment (Envirotech) Geological (Geotech) Household (Hometech) Industrial (Indutech) Medical & Hygiene (Medtech)
Samples Greenhouse cover, erosion preventive, decorative, artificial grass, pool isolation, rood bag, freeze/insect protector, crop cover Wall paper, heat isolation, roofing, pool isolation, bitumen felt, pipe cover, sound isolation Fusible interlining, wadding, shoes felt, toe-puff, counter environmental and safety textiles, such as filtration and insulation products for such uses as mopping up oil spills, etc; Geotextiles, membranes, drainage, filtration Under parquet felt, furniture and mattresses felts, pocked spring, floor covering, artificial leather backing, cleaning wipes, carpet backing, blind/shades Filters, abrasive, papermaking felt, CD cover, cable cover, battery separator, reinforced plastic, self adhesive tape, greaser pad, flame barrier isolator, ironing felt Surgical wear, coverlet, cleaning wipes, bone, mask, bandage, filter, pad
Transport (Mobiltech)
Sound and heat isolator, molded felt, carped, brake lining, head liner
Packaging (Packtech)
Breathable webs, water and humidity blocker, flame retardant web, envelop, harmful material packaging
Protection (Protech)
Safety cloths, head and moisture barrier, awning, tent, sleeping bag
Sports (Sporttech)
Wind proof web, breathable web, heat isolator
Oil (Oekotech)
Oil absorber web
14
High Performance and High Temperature Re sistant Fibers es
3
High Performance and High Temperature Resistant Fibers
Faster, stronger, lighter, safer ... these demands are constantly being pushed upon today's researchers and manufacturers, including protective clothing - routine or specialized. High performance and high temperature resistant fibers allow products to meet these challenges. The markets and products which are facilitated by the use of these fibers go far beyond the scope and awareness of most people [128].
Before exploring details these materials, it is important to define the parameters of high performance and high temperature resistant fibers. For this discussion, the latter is classified as a synthetic fiber with a continuous operating temperature ranging from 375˚ F to 600˚ F. The classification of high performance is less rigid and can be broken down into various segments. Generally speaking, fibers are said to be either commodity or high performance (see Table. III). Commodity fibers are typically used in a highly competitive price environment which translates into large scale high volume programs in order to compensate for the (often) low margins. Conversely, high performance fibers are driven by special technical
functions
that
require
specific
physical
properties unique to these fibers. Some of the most prominent 15
Introduction and Literature Review
of these properties are: tensile strength, operating temperature, limiting oxygen index and chemical resistance. Each fiber has a unique combination of the above properties which allows it to fill a niche in the high performance fiber spectrum [128]. Table III: Some of the basic characteristics of commodity & high performance fibers classification.
Commodity fibers
High performance fibers
Volume Driven
Technically Driven
Price Oriented
Specialty Oriented
Large Scale, line-type production
Smaller batch-type production
Basic Properties Tensile strength is often the determining factor in choosing a fiber for a specific need. A major advantage of high strength fibers is the superior strength-to-weight ratio that such fibers can offer. Paraaramid fiber offers 6-8 times higher tensile strength and over twice the modulus of steel, at only one-fifth the weight, but in applications where strength is not of paramount importance, other properties must be evaluated. Temperature resistance often plays an integral role in the selection of a fiber. Heat degrades fibers at different rates depending on the fiber type, atmospheric conditions and time of exposure. The key property for high temperature resistant fibers is their continuous operating temperature. Fibers can survive exposure to temperatures above their continuous operating temperatures, but the high heat will 16
High Performance and High Temperature Resistant Fibers
begin to degrade the fiber. This degradation has the effect of reducing the tensile properties of the fiber and ultimately destroying its integrity. A common mistake is to confuse temperature resistance with flame retardant ability. Flame retardant ability is generally measured by the Limiting Oxygen Index. LOI, basically, is the amount of oxygen needed in the atmosphere to support combustion. Fibers with a Limiting Oxygen Index (LOI) greater than 25 are said to be flame retardant, that is there must be at least 25% oxygen present in order for them to burn. The LOI of a fiber can be influenced by adding a flame retardant finish to the fiber. FR chemicals are either added to the polymer solution before extruding the fiber or added to the fiber during the spinning (extrusion) process. In addition, impregnating or topically treating the fiber or the fabric, flame retardant properties are often added directly to fabrics (such as FR treating cotton fabrics). Just as heat can degrade a fiber, chemical exposure, such as contact with acids or alkalis, can have a similar effect. Some fibers, (i.e. DuPont’s Teflon), are extremely resistant to chemicals. Others lose strength and integrity quite rapidly depending on the type of chemical and the degree of concentration of the chemical or compound [128].
17
Introduction and Literature Review
Fiber Forms and Product Forms Fibers are available in several different forms. The most common forms used are: − Staple Fiber – filaments cut into specific lengths – usually spun into yarn − Chopped Fiber – coarser, cut to specific, often short, lengths to add to mixture − Monofilament – a single (large) continuous filament yarn – like fishing line − Multifilament – extruded continuously with many filaments in the bundle. These basic forms of fiber are then further processed into one of four major converted forms. These converted forms can be categorized into four groups: − Spun yarn − Knitted fabric − Woven fabric − Nonwoven fabric Most are familiar with yarn, woven and knitted fabrics. Nonwoven fabrics may be another story. The most common types of nonwoven fabrics are – based on bonding and manufacturing processes - are: − Needlefelts – the fibers are mechanically entangled with barbed needles
18
High Performance and High Temperature Resistant Fibers
− Dry-laid – chemical or thermal bond – many different forms, including − Direct formed - spunbond and melt-blown (may be further bonded or combined) − Stitch Bond – sewn bond − Wet-laid – paper making process − Hydro-entangled (spunlace) – water jet entangled – mechanical bond Many of the fibers are used in very similar end uses, but based on differences of specific properties; each fiber tends to find its own niche where it has an advantage over the others. High performance fibers and high temperature resistant fibers offer numerous advantages over traditional materials. Higher strength, lighter weight, higher operating temperatures and flameretardant ability are some of the most prominent features of these fibers.
These
outstanding
properties
create
opportunities
to
manufacture products that historically could not be made due to technical constraints. The protective clothing area is one of those markets. Each of these fibers discussed have their limitations. It is not as easy to take these materials “off the shelf” except for a few welldistributed ones. Surely, some are more readily available than others - the aramids, HDPE, for instance -- but most are less so and should be considered as engineering or specialized materials to be used
19
Introduction and Literature Review
where their properties are paramount. Review thoroughly each fiber for the properties it brings to the product. High performance fibers allow companies to enter niche markets, which typically provide higher profits as well as strong barriers to entry for the competition. Even in the high performance area, many markets have become "commodity" applications, particularly the aramids in protective clothing. The protective clothing market will continue to bring new opportunities for high performance fibers as the fiber manufacturers expand their current product lines as well as create new and exciting specialized materials [128].
20
High Performance and High Temperature Resistant Fibers
Fiber Properties and Their Applications 3.1. Meta-Aramide; Nomex® (Dupont) 3.1.1. What Is NOMEX? NOMEX® is a DuPont registered trademark for its family of aromatic polyamide (aramid) fibers. This family consists of staple fibers, continuous filament yarns, paper, and spunlaced fabrics. Uses for staple, yarn, and spunlaced products include apparel fabrics to protect against flash fire and electric arc exposure; firefighter garments; fabrics and spun yarns for filtration applications; insulation in fire resistant thermal protective apparel; rubber reinforcement; and in transportation textiles such as aircraft carpeting. Unlike flame-retardant treated (FRT) materials, NOMEX® brand fibers are inherently flame resistant (FR): the flame resistance is an inherent property of the polymer chemistry [30]. Meta-aramids are best known for their combination of heat resistance and strength. In addition, meta-aramid fibers do not ignite, melt or drip; a major reason for their success in the FR apparel market. In comparison to commodity fibers, meta-aramids offer better long-term retention of mechanical properties at elevated temperatures. Meta-aramids have a relatively soft hand and tend to process very similarly to conventional fibers, giving them a wide range of converted products. For more properties see (Table. IV). Metaaramids are available in a variety of forms, anti-stat, conductive, in blends (with other high performance fibers), etc [128]. 21
Introduction and Literature Review
Table IV: Typical properties of meta-aramide fibers [128]. M-Aramid Properties
Value
Tenacity ( g/de )
3.8 – 7.2
Elongation ( % )
25 – 40
Limiting Oxygen Index
30
Chemical Resistance
Mild – Good
Operating Temperature
400˚C
Density (g/cm3)
1.38 at 21 ˚C (70 ˚F )
The product lines of Nomex® have been augmented to include a variety of natural and colored fibers and blends, each with unique properties designed to meet specific end-use requirements [30]. For more than 30 years, protective apparel made from Dupont™ Nomex® brand fiber has provided superior thermal protection from flames, flash, fires and electric arts. The unique molecular structure of Nomex makes it inherently flame resistant. Garments
of
NOMEX®
consistently
provide
outstanding thermal performance because NOMEX® [29]: •
Is inherently flame resistant.
•
Does not burn or melt and drip.
•
Provides permanent protection that won’t wash out or wear away.
•
Minimizes break-open and maintains a stable, inert barrier between the fire/arc and skin, protecting the wearer from direct exposure.
22
High Performance and High Temperature Resistant Fibers
•
Forms a tough, protective char when exposed to flame, and stays supple until it cools.
•
Meets NFPA 1975 for firefighters’ station wear.
•
Meets the ASTM F-1506 standard for workers’ apparel as protection from electric arc exposure. Table V: Typical Applications for Meta-aramid Fabrics [128] (Not an exhaustive list) M-Aramid Fabric From
Application
Needlefelt
• • • • • • •
Automotive Business machine parts Cushion material Hot gas filtration Safety & protective clothing Thermal insulation Thermal spacers
Woven fabric
• • • • •
Hot gas filtration Loudspeaker components Reinforcement; composites and rubber Safety & protective clothing Thermal insulation
Wet-laid nonwoven
• • •
Business machine parts Battery separators Heat shields
Dry laid nonwovens
• • • • • •
Business machine parts Electrical insulation Heat shields Hot gas filtration Laminate support base Thermal spacers
Spunlace nonwoven
• • •
High temperature filtration Safety & protective clothing Laminate support base
23
Introduction and Literature Review
3.1.2. Development and Molecular Structure of NOMEX® Brand Fiber NOMEX® was developed by a DuPont research team seeking a fiber which would add thermal resistance to the physical properties of nylon. NOMEX®
meta-aramid
is
prepared
from
meta-
phenylenediamine and isophthaloyl chloride in an amide solvent. It is a long chain polyamide in which at least 85% of the amide linkages are attached directly to two aromatic rings. The aromatic rings and the conjugated amide bonds that link them together are particularly strong and resistant to chemical attack. They also provide a high degree of heat resistance to the polymer backbone. As a result, NOMEX® does not melt and drip, and merely chars when exposed to high temperatures for prolonged periods [30].
Figure (3): NOMEX® meta-aramid [poly (meta-phenyleneisophthalamide)].
24
High Performance and High Temperature Resistant Fibers
3.1.3. Durability and Cost Effectiveness Garments made with NOMEX® thermal technology are extremely durable and resist abrasion, tears and chemicals. They’re also an excellent value, lasting three to five times longer than other standard and protective fabrics, including 100% cotton and flameretardant treated (FRT) cotton. In lease, rental and purchase programs, the outstanding wear life of garments of NOMEX® can contribute to bottom-line savings. 3.1.4 Lightweight Comfort Garments of NOMEX® are as comfortable to wear as other work clothing. Lightweight, breathable fabrics of NOMEX® brand fiber are designed to transport moisture away from the skin, which helps wearers feel cool and dry. Side-by-side wear tests show that fabric weight is the single greatest factor in controlling garment comfort, and that the lightweight comfort of NOMEX® is often preferred over other protective fabrics. In addition, protective apparel of NOMEX® is available in a variety of fabric weights to suit any climate. 3.1.5 Professional Appearance Flame-resistant protective apparel of NOMEX® combines style and functionality with a professional appearance. NOMEX® is available in a wide range of colors and garment styles, including jackets, parkas, slacks, jeans, shirts, polar fleece and switching coats.
25
Introduction and Literature Review
3.1.6 Easy Care Garments of NOMEX® are easy to launder and rarely need pressing. Normal home or commercial laundering and dry cleaning techniques provide good results. The protection is permanent and cannot be washed out or worn away [29]. 3.1.7 Fiber Properties NOMEX® brand fiber, a member of the aramid family of fibers, offers excellent flame resistance, good textile properties, dimensional stability, and resistance to degradation by a wide range of chemicals and industrial solvents. Most varieties have an oval to dogbone fiber cross-section (fig. 4).
Figure (4): Photomicrograph of a Typical Cross Section of Nomex
26
High Performance and High Temperature Resistant Fibers
Effect of Dry Heat Nomex does not melt or drip. It does not show a defined melting point. The strength retention of Nomex when exposed to heat is a function of time, temperature and environment. Nomex has good stress-strain properties at temperatures above the melting point of most other synthetic fibers. Increasing temperature reduces the tensile strength, modulus, and break elongation of yarn of Nomex. Nomex has a breaking strength ~50% of the approximate melting point of Nylon and Polyester fibers at room temperature [30]. Effect of Moisture The presence of small amounts of water vapor in air or other gases has no apparent effect on the strength properties of NOMEX®, even at elevated temperatures. Variations in relative humidity from 5% to 95% have virtually no measurable effect on the strength of NOMEX® at room temperature. The moisture regain of NOMEX® is significantly greater than that of polyester, slightly higher than that of nylon, and less than that of cotton. The longitudinal stability of NOMEX® brand fiber is virtually unaffected by changes in relative humidity.
27
Introduction and Literature Review
Longer exposure to dry air at 500˚CF (260˚C), have essentially no further effect on yarn length. A combination of moisture and heat produces greater shrinkage of NOMEX fiber than dry heat alone because it more fully releases internal fiber stresses. Woven fabrics of NOMEX® exhibit a low level of shrinkage when laundered. In a laboratory test, fabrics of NOMEX® were commercially laundered at 160˚F (71˚C). After five launderings, both shirt-weight (4.5 oz/yd2) and pant weight (6.0 oz/yd2) fabrics shrunk an average of 2% in both the warp and fill direction. No additional shrinkage was seen in 45 subsequent launderings. 3.1.8. Flammability, Smoke and Off-Gas Generation The
Limiting
Oxygen
Index
(LOI)
of
NOMEX®
is
approximately 28. Thus, when exposed to flame at room temperature in a normal air environment, NOMEX® will not continue to burn when the flame is removed. At temperatures above approximately 800˚F (427˚C), NOMEX® carbonizes and forms a tough char. The composition and quantity of off-gases varies widely depending on rate of heating, presence of oxygen and other factors. Burning NOMEX® brand fiber produces combustion products similar to those of wood, wool, cotton, polyester and acrylic. At combustion temperatures, NOMEX® releases carbon dioxide and carbon monoxide; and, sometimes traces of hydrogen cyanide and nitrogen oxides are detected. Under less stringent heating conditions, NOMEX® degrades very slowly, releasing small quantities of a wide variety of organic 28
High Performance and High Temperature Resistant Fibers
compounds. These may include carbon dioxide, acetone, acetamide, acetaldehyde, benzene, butane, toluene and many other compounds in trace amounts depending on exposure conditions. 3.1.9. Resistance to Degradation Abrasion Abrasion resistance is an important consideration in both protective apparel and filtration applications. Abrasion from wear and laundering is a primary cause of garment failure, while abrasion from dust exposure and cage wear often leads to filter bag failure. Woven fabrics made from spun staple yarns of NOMEX® consistently exhibit abrasion resistance superior to comparable, or in some cases, even heavier constructions of polyester/cotton blends and 100% cotton[30]. Laundry and Wear Life/Wash and Care Nomex limited wear can be laundered because the inherent flame resistance of Nomex can not be washed. Garments made with Nomex are made to last and are easy to maintain. They can be commercially laundered or dry-cleaned, using conventional methods without altering their ability to protect the wearer against heat and flame. Nomex fabrics undergo minimal shrinkage (maximum 3%) and maintain their original size and shape over the life of a garment. In fact, Nomex garments come out of the dryer ready to wear and rarely require ironing [29]. 29
Introduction and Literature Review
3.1.10. Some Guidelines about Washing and Drying of Nomex Garment. 4.1.10.1 Temperature and Duration of washing and drying cycles − It is adequate to wash Nomex garments at 60˚C. Using a higher temperature may not bring any benefit, and indeed may simply contribute to overall energy consumption. Always observe the washing recommendation of the garment manufacturer. − The washing cycle should not exceed 1 hour. − It is important to include rinse cycle that adequately removes residual soap and detergent. − Drying can be done in a tumble drier and temperatures normally used are 60˚C in industrial laundry environments. − The important factor in drying is not to over dry. It is better to give the garments a shorter drying cycle and remove them while still slightly damp, than to remove them bone-dry. This is because excessive agitation can cause localized damage such as abrasion. 3.1.10.2 PH of Soaps and Detergents − Best is to use a liquid detergent with a near neutral PH, certainly not exceeding PH 9.0. Liquids can be more easily handled then powered soaps. − If localized dirty oil stains are difficult to remove, they can be treated, before putting into the washing machine, with neat liquid soap applied to the locality of stains and light rubbing to assist the action of the soap. 30
High Performance and High Temperature Resistant Fibers
− It is known that particular attention must be given to PH of soaps used with garments in colors of navy blue, royal blue, greens and grey, and in these cases it is best to select soaps and detergents with PH of 8.0 or below. − Nomex garments should never be bleached by any chlorine bleach or strong oxidizing agent such as peroxide, and under no circumstances should caustic washing agents be used. 3.1.10.3 Appearance While protection rates top priority, smart appearance is also important. Dupont works with textile producers to develop a wide range of types and weights of fabric and with garment manufacturers to come up with attractive, varied styling [61]. 3.1.10.4 Cost Effectiveness The purchase of protective apparel is an investment in safety. A lower initial purchase price does not mean the best value in the long run. Nomex garments are extremely hard-wearing and resistant to tear and abrasion, providing the same high level of protection over many years of wear. The cost of Nomex garments is typically higher than protective apparel made from treated or chemically altered fabrics. However, they prove to be cost effective in the long run. It has been demonstrated that the wear life of Nomex garments is three to five times that of similar garments made of blended or treated fabrics. On a long-term cost basis, selecting protective solutions made of Nomex
31
Introduction and Literature Review
can actually reduce clothing budgets and at the same time provide superior levels of protection, comfort and good looks [62].
3.2. Polyimide (PI): P84 P84 is a polyimide fiber developed by Lenzing AG (Austria) in the second half of the 1980s [41] and now produced and marketed by a spin-off company, Inspec Fibers GmbH in Austria. P-84 provides a high operating temperature with very good flame retardant properties and good chemical resistance. P-84 fiber touts a unique multi-lobal irregular cross section. This irregular structure offers greater surface area than a conventional round cross section, and has achieved widespread recognition for P-84 fiber in the hot gas filtration market. Due to its high price however, actual use of P-84 in the filtration market is limited to areas where extreme emission controls are necessary. It has also made inroads in the protective clothing market, especially in Europe
[128].
The polymer is fully imidized and can be
directly converted into fibers by a dry spinning process [43]. Table VI: Typical Properties of Polyimide (PI); p-84 Fiber [72]. P-84 Properties
Value
Tenacity g/de
4.2
Elongation (%)
30
Continuous operation temperature (˚F)
500
Limiting Oxygen Index (%)
38
Chemical resistance
Good
Shrinkage (240˚C , 15 min)
< 3%
Density
1.41 g/cm3
Glass Transition Temperature
315˚C - 599˚F
32
High Performance and High Temperature Resistant Fibers
Table VII: Typical applications for p-84 polyimide fabrics [72]. Form
Application
Needle felt
• •
Thermal insulation Safety & protective clothing
Woven Fabric
• •
Thermal insulation Safety & protective clothing
3.2.1. Fiber Properties Features of the P84 polyimide fibers are the irregularly lobed cross-section being responsible for the high bulk of the fibers. Because of the low modulus and the high elongation P84 polyimide fibers are not destined for typical “reinforcing” applications as Paramide or carbon fibers [70]. P84 is composed of aromatic backbone units only. Therefore it is a recommended material for high temperature applications (Fig. 5). Despite the aromatic, halogen free structure it is classified as non flammable with a limiting oxygen index (LOI) of 38 % [72].
Figure (5): P84 Chemical Structure
33
Introduction and Literature Review
The aromatic halogen-free polymer is manufactured by polycondensation
of
an
anhydride
(BTDA)
Benzophenone
tetracarboxylic dianhydride with aromatic diisocyanates in high polar solvents like dimethylformamide (DMF) or dimethylacetamide (DMAC) (Fig. 6) [43].
Figure (6): Monomers used for manufacturing of P84 polymer.
3.2.2. Cross Section of P84 Fibers P84 fibers are easily recognized by the fiber cross-section. By applying special parameters in the spinning processes irregular crosssections are obtained which cause a much higher specific fiber surface compared to round or shaped fibers with the same fitness [43]. The unique multilobal cross section offers up to 90 % more surface area compared to conventional round fibers and is the key advantage of P84. This increased surface area results in the highest filtration efficiency of conventional fibers, even for sub micron
34
High Performance and High Temperature Resistant Fibers
particles. The fibers meet the requirements of all common textile processing steps. Besides standard grades, micro denier fibers are part of the production range (Fig. 7) [72].
Figure (7): P84 Fibers Cross Section.
As the values indicate P84 is a typical textile fiber not comparable with reinforcing fibers with high modulus and low elongation but are used in a variety of textile or technical end uses where sufficient tenacity and flexibility in combination with temperature resistance is required. 3.2.3. The Thermal Properties The thermal properties of the fully amorphous polymer are characterised by the glass transition point of 315 °C which enables a continuous fibre application temperature of 250 °C. The fibers do not melt but decompose and carbonize at elevated temperatures 35
[43].
Introduction and Literature Review
When subjected to high temperatures, P84 degrades the same way as many other organic polymers leaving a carbon structure. However, the decomposition temperature is extremely high as shown in (fig. 8).
Figure (8): Short Term Temperature Stability of P84 [72]
The weight loss of P84 is recorded versus time at different temperature. Up to a temperature of 350˚C (662˚F) the weight loss is below 3% corresponds to the moisture content of the fiber [72].
Figure (9): Isothermal thermo gravimetric analysis of p84 fibers [43].
36
High Performance and High Temperature Resistant Fibers
Figure.9 shows an isothermal thermo gravimetric analysis (TGA) where the weight of the fiber as a function of time at different temperatures is described. Whereas at 350 °C the weight loss after 3 hours is around 5 %, at 500 °C a value of 50 % is already attained after 70 minutes. Another feature of the polyimide fibers is there inherent non flammability. P84 is one of the organic fibers with the highest LOI (Limiting Oxygen Index) of 38%. LOI is the level of oxygen in the oxygen/nitrogen mixture of air, expressed as percentage, that must be present the fiber would ignite and burn when exposed to a flame. To be self extinguishing the LOI has to be higher than 25% oxygen [43].
Figure (10): Limiting Oxygen Index (LOI) of Fibers. The LOI indicates the level of oxygen needed to keep the material burning after ignition. P84 is classified as non flammable in atmospheric conditions [72].
The increased surface has a beneficial effect especially on filtration performance but is also responsible for bulky high volume yarns and nonwovens useful in thermal insulation jobs. P84 polyimide fibers are manufactured as staples in titres from 0, 6 to 8, 0 dtex and as multifilament of 1060 dtex. The color of the fibers is 37
Introduction and Literature Review
yellow based on the chemical structure of the polymer. For applications where colors are required organic pigments can be added to the dope to meet especially dark color shades. During the manufacturing process the fibers are stretched and the polymer molecules oriented to a certain extent. When exposing the fibers to temperatures near the glass transition temperatures a reorientation of the molecules takes place and the fibers shrink. The diagram shows the significant increase of the shrinkage after 30 minutes exposure at temperatures at and beyond 315 °C (599 °F) [72].
Figure (11): P84 fiber shrinkage characteristics duration: 30 min [72]
3.2.4. Applications Because of the high fiber price the usage of the polyimide fibers is limited to those applications where their excellent properties such as thermal stability are required.
38
High Performance and High Temperature Resistant Fibers
High temperature filtration: The filtration of flue gases of waste incineration, coal fired boilers, cement kilns or asphalt plants are the most successful application of P84 fibers. The higher specific surface compared to other available fibers provide advantages in filtration efficiency at low differential pressures. The majority of used media is based on nonwovens manufactured by needle punching technology and consists of carrier fabrics where fiber layers are needled on. These fabrics could be made of P84 spun or multifilament yarns. On the other hand also scrims less versions of filter media are available. The felts in average have a weight per area of 500 g/m², tensile strengths beyond 800 N/5cm and air permeabilities of app. 200 l/dm².min. Additional steps in the manufacturing process are the singing to reduce the hairiness of the surfaceand the calendaring. The outstanding filtration characteristics of media containing P84 fibers have been proved not only in many reference installations in the industry but also in lab tests under controlled and standardized conditions. The good experience with the high dust collection efficiency of polyimide fibers lead to filter media where P84 is blended to other fibers either uniformly or especially on the surface on the flue gas side.
39
Introduction and Literature Review
3.2.5. Sealing applications: The P84 sealing is used because of its stability at high temperature and chemical resistance against hot oil. The fixing of the P84 seal onto the cartridge is done by melting the polyamide into the polyimide felt ring. As the temperature applied is in the range of app. 250 °C the thermo stable P84 is the material of choice. The advantage of this new concept of oil filters is the easy and environmental friendly disposal of the used cartridges by combustion without ash remaining. Thermal insulation/structural elements: Polyimide fibers show a tendency to shrink extensively if heated above the glass transition temperature of 315 °C. By varying the temperature and the type of initial fiber structure (nonwoven, fabric, knit wear etc.) it is possible to produce light weight but stable mechanical structures which reach the stiffness of thermoplastic LDPE without additional adhesives or binders. During the heat treatment high contraction forces occurs generating bonds between the single fibers forming these self supporting structures. Using a nonwoven the structure is designed by the density and thickness of the felt, the temperature of the process and the allowed rate of shrinkage [43]. 3.2.6. Protective Clothing: The soft handle of P84 polyimide fibers additional to the thermo stable and non flammable properties is the reason for their usage in protective clothing. When new European standards for fire fighter clothing were introduced heat insulation materials became 40
High Performance and High Temperature Resistant Fibers
important. Polyimide fibre heat insulation systems such as the P84 Liner meet all demands of this standard with regards to mechanical and thermal stress. The P84 liner consists of a needle felt of polyimide fibers (weight: 200 g/m²) quilted with a marine blue colored face cloth of 110 g/m² out of 33 % P84 and 67 % flame retardant viscose. The flexible liner system offers protection against fire and heat also after several washings. Summary: Synthetic fibers based on aromatic polyimide polymer have been used in a wide range of applications due to their excellent properties, such as heat resistance, flame retardancy or non melting behavior. The irregular lobed cross section being responsible for the increased specific surface makes P84 the first choice high temperature fiber with excellent dust collection capabilities. The possibility to form self supporting structures by heat treatment of P84 fiber layers has not been used to a high extent, but offers a future in insulating performance combined with design freedom and assembly advantages [43].
41
Introduction and Literature Review
3.3. Glass Fiber: Fiberglass (also called fiberglass and glass fiber) is material made from extremely fine fibers of glass. It is used as a reinforcing agent for many polymer products; the resulting composite material, properly known as fiber-reinforced polymer (FRP) or glassreinforced plastic (GRP) is called 'fiberglass' in popular [94]. Glass is an inorganic fiber, which is neither oriented nor crystalline. Glass fibers were on of the first ''man-made" fibers, commercialized in the late 30's. Widely used as insulation (glass batts in home insulation and industrial insulation in mast and fabric form). It is widely used in reinforcing thermoplastic composites in products form circuit boards to boat hulls. High temperature filtration is another high volume use. The ingredients normally used in making glass fibers are: silicon dioxide, calcium oxide, baron oxide, plus a few other metal oxides [128]. Glass as material is perhaps as old as civilization itself, but of glass as a reinforcing material is relatively modern idea. In the Egyptian and Syrian histories of the 16th and 17th centuries, glass fiber was referred to as material used for decorative items. In 1893, a beautiful glass fibre dress was exhibited as the Columbian Exposition in Chicago
[113].
Glass is an inorganic fibre which is neither oriented
nor crystalline the high-performance potential of glass fibre was first realized in 1920 from the pioneering work of Griffith
[44].
Glass used
as high-performance fibre is made from similar ingredients to any other glass material. However, the choice and composition of
42
High Performance and High Temperature Resistant Fibers
ingredients varies to some extent depending on the end use requirements
[49].
The ingredients normally used in making glass
fibers are: silicon dioxide, calcium oxide, aluminum oxide, boron oxide plus a few other metal oxides. Structurally, glass has an isotropic three-dimensional network based on a tetrahedron of four oxygen atoms around a silicon atom, but made irregular and amorphous by metal ions [47]. Over the last two decades, glass fibre has lost its market share to aramids and carbon fibers in the area of advanced fiber reinforced composites. However, even today, glass is the most important reinforcing fibre in volume terms
[99].
Over the last 10 year the
consumption of glass fibre has grown by 8-10% on an average each year. Various authors
[15, 79]
have reviewed the overall scope of glass
fibers in textiles and composites with appropriate discussions on the production methods, properties, fields of application and the various test procedures used to analyse the materials from fibre to fabric. There are two common fiberglass products; •
Continuous or woven glass filament, used as a reinforcement material in fiberglass pools, boats, tanks and other hard synthetic products.
•
Glass wool – such as batts – used for heat and sound insulation in buildings.
43
Introduction and Literature Review
Continuous glass filament is made by extruding molten glass through very fine holes to form thin strands. Glass wool is made by spinning or blowing molten glass.
Figure (12): fiberglass continuous filaments. Theses are twisted together to form yarns and threads for the manufacture of textiles [88].
Continuous filaments can be woven in a variety of fabrics of differing configurations as shown in (fig. 12). For example, stain weaves are chosen where drape onto a mould surface without distortion of the fiber orientation is required and therefore are often used in advanced composites in the form of prepreg. The weave pattern can be chosen to ensure appropriate fiber orientation in the
44
High Performance and High Temperature Resistant Fibers
moulding. The properties of a fiber composite are dominated by the alignment of the fibers to the principal stress axes [107].
Figure (13): schematic of glass fiber fabric weaves [107].
45
Introduction and Literature Review
Fiberglass can be divided into two groups; − "Traditional " fiberglass which has been used since early in the 20th century ; and − "Biosoluble" fiberglass which is made from new materials that disappear from the body much more rapidly than the “traditional ". The entire fiberglass manufactured in Australia since January 2001 has been of the “biosoluble " type [26].
Figure (14): fiberglass staple fiber can be twisted and plied into yarns [88].
46
High Performance and High Temperature Resistant Fibers
3.3.1. Fiber Types & Composition: Silica is the basis for all commercial glasses. They are obtained by fusing a mixture of materials (various oxides) at temperatures ranging from 1300˚ to 1600˚ C. There are different types of glass fibers commercially available all of which have different compositions and very often specific technical significance. The following is an outline of some of the popular varieties of glass [80, 128]; A- alkali-containing glass composition. AR- alkali –resistant for reinforcing cement. C- chemically –resistant glass composition. E- standard uses, this composition has high electrical resistance. HS- magnesium-alumina-silica glass. High strength. S- composition similar to HS glass. High- performance fibers are normally made in the form of continuous strands. Over 90% of all continuous glass fibers produced are E glass composition 'E' glass is commonly used for reinforcement purposes in the glass reinforced plastics (GRP) industry. More recently developed ' AR' glass fibers are used for reinforcing inorganic hydraulic cement-based materials to improve their resistance against tension and impact [95]. AR-glass contains a significant proportion of Zr02 in its composition. Its resistance to alkali derives from the formation of a passive layer enriched with Zr02 in the surface of the fibre
[130].
The
production and various compositions of glass fibers which are particularly suitable for use as reinforcing fibers in compositions of 47
Introduction and Literature Review
glass fibers which are particularly suitable for use as reinforcing fibers in composites were reviewed by Ohta [81]. 3.3.2. Formation: Glass fiber is formed when thin strand of silica –based or other formulation glass is extruded into many fibers with small diameters suitable for textile processing. Glass is unlike other polymers in that, even as a fiber, it has little crystalline structure. The properties of the structure of glass in its softened stage are very much like its properties when spun into fiber. One definition of glass is “an inorganic substance” in a condition which is continuous with, and analogous to the liquid state of that substance, but which, as a result of a reversible change in viscosity during cooling, has attained so high a degree of viscosity as to be for all practical purposes rigid [94]. The technique of heating and drawing glass into fine fibers has been known to exist for thousands of years ; however , the concept of using these fibers for textile applications is more recent . The first commercial production of fiberglass was in 1936. In 1936, Owensillinois Glass Company and Corning Glass Works joined to form the Owensorning Fiberglass Corporation. Until this time all fiberglass had been manufactured as staple. When the two companies joined together to produce and promote fiberglass, ether to produce and promote fiberglass, they introduced continuous filament glass fibers
[94].
Owens-Corning is still the major fiberglass
producer in the market today.
48
High Performance and High Temperature Resistant Fibers
3.3.3. Chemistry: The basis of textile grade glass fibers is silica, SiO2. In its pure form it exists as a polymer, (SiO2) n. It has no true melting point but softens up to 2000˚ C, where it starts to degrade. At 1713˚ C, most of the molecules can move about freely. If the glass is then cooled quickly they will be unable to form an ordered structure
[45].
In the
polymer it forms SiO4 groups which are configured as a tetrahedron with the silicon atom at the center, and four oxygen atoms at the corners. These atoms then form a network bonded at the corners by sharing the oxygen atoms. The Vitreous and crystalline states of silica (glass and quartz) have similar energy levels on a molecular basis, also implying that the glassy form is extremely stable. In order to induce crystallization, it must be heated to temperatures above 1200˚ C for long periods of time [94].
Figure (15): Glass Tetra.
49
Introduction and Literature Review
3.3.4. Molecular Structure of Glass: Although pure silica is a perfectly viable glass fiber, it must be worked with at very high temperatures which are a drawback unless its specific chemical properties are needed. It is usual to introduce impurities into the glass in the form of other materials, to lower its working temperature. These materials also impart various other properties to the glass which may be beneficial in different applications. The first type of glass used for fiber was soda-lime glass or A glass. It was not very resistant to alkali. A new type, E-glass was formed that is alkali free (
