Mechanical and thermal conductivity properties of ...

Accepted Manuscript Title: Mechanical and thermal conductivity properties of hemp fiber reinforced polyurethane composites Authors: S. Sair, A. Oushabi, A. Kammouni, O. Tanane, Y. Abboud, A. El Bouari PII: DOI: Reference:

S2214-5095(17)30221-8 https://doi.org/10.1016/j.cscm.2018.02.001 CSCM 143

To appear in: Received date: Revised date: Accepted date:

24-10-2017 24-1-2018 2-2-2018

Please cite this article as: Sair S, Oushabi A, Kammouni A, Tanane O, Abboud Y, El Bouari A.Mechanical and thermal conductivity properties of hemp fiber reinforced polyurethane composites.Case Studies in Construction Materials https://doi.org/10.1016/j.cscm.2018.02.001 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Mechanical and thermal conductivity properties of hemp fiber reinforced polyurethane composites S. Sair1*, A.Oushabi1, A.Kammouni1, O. Tanane1, Y. Abboud1, A. El Bouari1 University Hassan II of Casablanca, Faculty of Sciences Ben M’sik, Laboratory of Physical Chemistry of Applied Materials (LPCMA), Driss El Harti, B.P 7955, Sidi Othmane Casablanca. 1

*Corresponding author: [email protected] (Tel:+212 6 62 47 39 06).

IP T

Abstract: The aim of the present work is to introduce natural hemp fiber as reinforcement in the

preparation of partially biodegradable green composites. Composite of rigid polyurethane (PU) and

hemp fiber (H.F) were prepared at different loading rates in (H.F) (5%, 10%, 15%, 20%, 25% and

SC R

30%). Water absorption, thermal conductivity, and mechanical properties of composite were

investigated as a function of fiber content. The results show that, the thermal conductivity of composites increases linearly with density. The mechanical properties of composites with 15% wt

U

fibers loading provided a 40% increase in strength. Measured properties showed that polyurethanehemp fibers composite present good insulating properties compared to the traditional insulation

N

materials (glass wool, mineral wool etc.). Therefore, (PU-HF) insulation may provide a promising

A

solution for building insulation.

1. Introduction

ED

properties, Water absorption.

M

Keywords: hemp fiber, Polyurethane resin, green composites, thermal conductivity, mechanical

Recently, the use of natural fibers has increased considerably due to its availability, low-density and

PT

price compared to synthetic fibers [1]. Those factors are responsible for the apparition of a new polymer science and engineering research. Natural fibers were introduced with the intention of

CC E

yielding lighter composites, coupled with lower costs, compared to the fiber glass reinforced polymer composites. Natural fibers have a lower density (1.2–1.6 g/cm3) than that of glass fiber (2.4 g/cm3), which ensures the production of lighter composites [2]. Conventional petroleum based epoxy resin [3, 4], polyurethane (PU), are used extensively with natural fibers, such as hemp, jute, sisal, and kenaf [5].

A

Recently, the rapidly expanding use of composite components in construction, sports, leisure, and other mass production industries, has been focused on sustainable and renewable reinforced composites [2, 5]. Building insulation is one of the most applications of this material, mechanical and thermal properties are the obvious needs in this area. Physical properties of polyurethane-based composites have been widely studied. Hadjadj et al. [6] demonstrated that Young’s modulus of PUAlfa fibers composite improved linearly with the embedded cellulose content, it increase by 250 % to 700 % when the fiber reinforcement is raised from 5 % to 30 %. Radzi et al. [7] have also studied the

influence of the addition of Roselle fiber on the mechanical and thermal properties of polyurethane composites they concluded that the tensile and fluxal strength increase with fibre contents, 40 wt% fibre content showed the highest strength. Oushabi et al. [8] studied the effect of polyurethane reinforced by date palm waste, they showed that this reinforcement affects the mechanical properties of the resulting composite, the thermal conductivity of prepared composite makes it possible to consider them as competitive for the development of effective, inexpensive insulating materials and safe. Silva et al. [9] studied the influence of Eucalyptus grandis fibers on rigid PUs and found that the

IP T

addition of 16% (m/m) natural fiber drastically increased their mechanical strength and thermal conductivity. Hemp fiber is one of important natural fibers used in industrial areas, which has relatively short cropping cycle and can be easily grown in a large array of environments. In addition,

SC R

hemp characterized by a tensile strength of up to 1110 MPa is one of the strongest fibers among all

bast fibers [10]. There are previous studies reporting on mechanical properties of PU-hemp fibers composites they concluded that treated hemp fibers with alkaline, silane or acetyl solutions can improve tensile and flexural properties of composites [11]. Several works are interested in the

U

mechanical behavior of polyurethane- natural fiber composites [12], but few have studied the effect of this reinforcement on the thermal conductivity. The aim of this paper is to study the properties of

N

hemp fibre (HF) reinforced (PU) composites with differential fibre contents (5, 10, 15, 20, 25 and 30

2.1. Composite preparation

M

2. Materials and methods

A

wt %). Mechanical, hygroscopic and thermal conductivity, of HF/ PU composites were examined.

ED

The precursors used in this work are illustrated in Fig.1; Hemp fibers with average density of 0.86 g/cm3, diameter of 22.5 µm, and length of 12 mm were obtained from Hempline Inc. The polyurethane

PT

was prepared by prepolymer of polyisocyanates and polyol. Polyisocyanates (ISONATE 181MDI Prepolymer) was supplied by DOW Chemical with 1.20 g/cm3 in a density and 23% in% NCO. Polyol (Krasol LBH 2000 Diol) was provided by CRAY VALLEY with a hydroxyl value of 0.91 Meq / g,

CC E

and density of 19-20g /cm3 at 20 ° C. The hemp fibers was chopped into 5–10 mm in length, treated with alkaline solution (8% of sodium hydroxide) then treated with a solution of 0.2 mol / l of 3aminopropyltrimethoxysilane according to previous work [13], the treated fibers and polyol are mixed under mechanical stirring for 20 min in order to homogenize the mixture, then the polyisocyanate was

A

added with ratio of polyol/polyisocyanates of 1/1, the product was poured into a 200×200×30 mm3 closed mold. Six PU-HF composites were prepared with different contents of hemp fiber: 0%wt, 5%wt, 10%wt,15%wt, 20%wt, 25%wt and 30%wt named PU (reference 1), PU5%, PU10%, PU15%, PU20% , PU25% and PU30% respectively. All composites were cured at ambient conditions for 48h. 2.2. Infrared spectroscopy

FTIR measurements were performed using a Mattson 7000 FTIR spectrometer. A total of 60 scans were taken for each sample with a resolution of 2 cm-1. 5.0 mg of the samples were ground and dried at 100 °C for 3 h to ensure that no water was adsorbed on the foam, then added to 200 mg of KBr a mixture was pressed into a disk. The spectra are saved for wavelengths from 4000 to 400 cm-1. 2.3. Water absorption The water absorption of the composite samples was measured according to ASTM D 2842-01 [14].

IP T

The size of the specimen was 40X40X20 mm. Water absorption tests were conducted by immersing the composite specimens in distilled water in beaker at room temperature for 7 days (168 h). At regular time intervals the specimens were taken out from the water and all surface water was removed

absorption W (%) are given by Eq.1: 𝑊(%) =

𝑚2−𝑚1 𝑚1

× 100 (Eq.1)

SC R

with a tissue paper. The specimens were reweighed then immersed again. The percentages of water

U

Where m1 and m2 are the weight of the dry and wet samples respectively.

N

Different models have been developed in order to describe the water absorption phenomenon of the

A

composite. The Fickian model is able to determinate the diffusion coefficient D (mm2/s) using the

M

Eq.2.

ℎƟ

ED

𝐷 = 𝜋(4𝑊𝑠) (Eq.2) Where:

Ɵ is the slope of the linear portion of the sorption curve



h is the initial sample thickness in mm.



Ws is the maximum weight gain of the sample

CC E

PT



The permeability coefficient P, (mm2/s), which implies the net effect of sorption S and diffusion D, is given by the Eq.3.

A

𝑃 = 𝐷 × 𝑆 (Eq.3)

Therefore, the sorption coefficients that are related to the equilibrium sorption of the principal penetrated, is calculated by the eq.4. 𝑆 = 𝑄𝑚/𝑄𝑡 (Eq.4) Where Qm and Qt are molar percentages of water uptake at infinite time and at time t. 2.4. Thermal conductivity

The thermal conductivity of polyurethane- hemp fiber composites was determined using a Thermal Conductivity Analyser (λ-Meter EP500e) showed in Fig.2. The thermal conductivity measurement consists in applying variable heat flux in a block comprising a sample of size 200 mm x 200 mm x 30 mm taken between two plates. The thermal conductivity is determined according to the standards ASTMC177 [15]. 2.5. Mechanical properties Tensile strength

IP T

2.5.1.

Young’s modulus and tensile strength were evaluated under a room temperature conditions. Five specimens were tested for each composite. Tensile tests were carried out according to ASTM

2.5.2.

SC R

D638[16] using a universal testing machine illustrated in Fig.3 (a) (Instron MPK universal.) at a crosshead speed of 1 mm/min. The Young’s modulus was calculated from the linear region of the stress–strain data. Flexural strength

U

The flexural test was performed by using a computer controlled universal testing machine

N

3R_Quantium of 10 KN load cell showed at Fig.3 (b). The ASTM D-790 [17] test method was followed, with a cross-head speed of 0.1 mm/s was applied. Five specimens of each sample were used

M

the following Eq.5 and Eq.6:

A

and average values are reported. The Bending stress 𝜎𝑓 and the flexural modulus 𝐸𝑓 are calculated by 3PL

ED

σf = 2bd2 (Eq.5) 𝐿3 𝑚

𝐸𝑓 = 4𝑏𝑑3 (Eq.6)

Where:

PT

P = load at the moment of fracture (N) L = the support span (m)

CC E

b = the width of beam tested (m) d = the depth of beam tested (m)

m = the slope of the initial straight-line portion of the load deflection curve (Nm–1 of deflection)

A

2.6. Scanning electron microscopy

The surface morphologies of hemp fibers, polyurethane and composite at 30% of fibers were examined using a Zeiss Gemini scanning electron microscope. 3. Results and Discussion 3.1. FT-IR Spectroscopy

Infrared spectroscopy was used to predict the bond between the matrix and the fibers, the FT-IR spectra of the treated fiber, neat polyurethane and PU-HF composites is illustrated in Fig. 4,The treated fiber shows bonds characteristic of the Si-O-C groups [18] at 1200 cm-1 and 780 cm-1, which confirms the reactivity of the silane precursors with the hemp fiber [19] the band at around 3600 cm -1 is attributed to the O-H bond of cellulose containing in hemp fiber. The polyurethane neat foam shows characteristic bonds at 2960 cm

-1

and 2280 cm

-1

corresponding respectively to the C-H and the

isocyanate -N = C = O bonds [20] [21], the intense bonds in the vicinity of 1650 cm -1, 1530 cm -1 and

IP T

1073 cm -1 are attributed to C = O links of carbonyl, C-N-H and C-O-C respectively [22] [23]. FT-IR spectra of the prepared composites, shows the existence of characteristic bonds of all constituents, the intensity of the band characterizing the isocyanate group decreases, which confirms the bond between

SC R

this entity and the hemp fibers . The optical microscope was used to observe the hemp fiber surface in

composite material, Fig.8a shows that the hemp fibers are inserted into matrix and their surfaces are fully covered, confirming the results of Infrared spectroscopy these results are in accordance with literatures [24] [25].

N

U

3.2. Thermal conductivity

Thermal conductivity is one of the most interesting characteristics for thermal insulation materials.

A

This property depends on several parameters such as a morphology [25], density and homogeneity of

M

materials [26]. The thermal conductivity curves of each prepared materials are shown in Fig.6, the value is obtained after the stabilization measurement time, and they are given with the values of the thermal resistance R and the density. From Table 1 it is noted that the thermal conductivity of the

ED

composites foams increases with loading rates in H.F. The order of the thermal insulation capacity of the composites is PU30% > PU25% > PU20% > PU15% > PU10%> PU5%. Compared with

PT

polyurethane PU, the thermal conductivity of sample PU5%, PU10%, PU15%, PU20%, PU25%, and PU30% are 10%, 13.7%, 21.5%, 24.5%, 29% and 33% higher respectively. The thermal resistance R evolves in opposite of the thermal conductivity. These results can be explained by the increase in the

CC E

density of prepared composites. The composites are mainly affected by fiber content; it increases with increasing hemp fibers content, indicating that hemp fiber has higher thermal conductivity than the polyurethane matrix. The low thermal conductivity value of the polyurethane is explained by its internal morphology showed in Fig.8b, indicate that this material has an alveolar structure with two

A

types of cells, opened and closed cells. Hemp fibers also exhibit a porous structure due to their multicellular morphology containing central void Fig.8d, the difference in thermal conductivity between the polyurethane matrix and hemp fibers is essentially due to the pore size of the two materials and the nature of the gas trapped by the polyurethane. The introduction of hemp fiber into the polyurethane matrix leads to an increase in the thermal conductivity. This result is observed in other work of polyurethane composite with other cellulosic

fibers [8] and is also encouraging since the thermal conductivity of the composite does not exceed 0.040 W / m.K at a density of 48.09 Kg.m-3. The composites prepared have two other advantages; Economical because they make it possible to reduce the cost of the polyurethane plate and ecological advantage since the fibers used are renewable materials. So the panel of the composite materials will consume less gray energy than before. 3.3. Water absorption

IP T

During their life cycle service, the composites materials are often exposed, for long periods, to humid environments. However, moisture generates heterogeneous internal stress fields in this type of material, which leads to the changes in thermal and mechanical properties. Thus, it is interesting to

SC R

predict the absorption of water for all formulations in order to estimate their sustainability.

Water uptake effects on thermal conductivity have been studied by [27] they reported that the thermal conductivity of composite materials increases with volumetric water content. The origin of this increase is due to the saturation in water, in this state the water occupies the open pores of the

U

materials. The increase in the conductivity is mainly due to the wide difference between that of the

N

water (0.6 W/m.K) and air (0.026 W/m.K).

A

The water uptake can also affect the mechanical properties of composite materials; the water

M

molecules change the structure and properties of the fibers, matrix and the interface between them, leading to the loss of compatibilization between the fibers and the matrix, to the chain reorientation and shrinkage of matrix also lead to the degradation of natural fibres by a hydrolysis mechanism. All

ED

these factors led to decrease mechanical properties of the composite. The water absorption amount was calculated by the weight difference between the samples exposed to

PT

water and the dried samples using the following Eq1. Water absorbed percentages in terms of a time for all samples are showed in Fig.6. The same behavior was observed for all samples, composite

CC E

materials absorbed water in two stages, and during the first stage (0-16 h) the speed of absorption is very fast reaching a certain value, then slows and approaches saturation after prolonged time following a Fickian diffusion process. Both the initial rate of water absorption and the maximum water uptake increase for all hemp fiber composites samples as the fibre content increases.

A

From sorption, diffusion and permeability coefficients values shown in Table 2 it is clear that the polyurethane absorbs less distilled water than prepared composites due to its closed cell structure which prevents water absorption and moisture storage. The incorporation of hemp fibers, highly hydrophilic, increase greatly the water content that can be retained by the composite materials, this behavior has been observed in other works of hemp fibers and polymer matrix composites [28, 29]. Water absorption increase at higher fiber content, the composite PU 30%, has the largest water uptake

and permeability coefficient, which limits the use of these renewable resources to high percentages exceeding 25%. 3.4. Mechanical properties The performance of materials is always presented in terms of their mechanical characteristics, such as tensile properties, flexural properties, compression properties, impact properties and wear behavior. It is evident from Fig.7 that all composites showed a ductile behavior, The properties of the

IP T

polyurethanes vary considerably with the fiber content [11, 12], reinforced composites with hemp fibers showed better tensile strength than the polymer matrix. The tensile strength of composites has

been found to increase with hemp fibers reinforcement. Composites with 15% loading exhibit

SC R

maximum tensile strength, followed by 10%, 5%, 20%, 25% and 30% loadings. The failure of reinforced composites under tensile load could be due to breaking of cellulosic fibers at the weaker

point followed by further propagation under the applied load that is transferred to adjacent fibers by the matrix, leading to complete rupture of the composites. From the value of Young’s modulus and

U

tensile strength reported in Table 3, it is clearly asserted that there is a gradual decrease in the strength

N

when increasing the percentage of the hemp fibers up to 20%. The tensile strength observed is better

A

at 15% hemp fiber.

The flexural strength results of hemp fiber composites follow the same trends obtained in tensile

M

strength tests. Table 4 show that the flexural properties increase up to 15% of fiber, and then keep this increase, after 20% of fiber we observed also the deterioration of the mechanical properties. Beyond

ED

20% the homogenization of the mixture being more difficult, the fibers are not all linked to each other by the matrix; this discontinuity of the fibers and the non-homogeneity which leads to the agglomeration of fibers has been detected by the scanning electron microscopy in Fig.8c, showing an

PT

area where the fibers were agglomerated when their content increases.

CC E

4. Conclusion

In this work, composite materials based on the polyurethane matrix and treated hemp fibers were studied with the aim of preparing thermal insulation materials for the building and public works sector, the foams developed in this work are a commercially viable and sustainable alternative to

A

conventionally produced polyurethanes. The results suggest that the thermal composite behavior evidence its application in thermal insulation, this finding can be supported by the lowe density values obtained. Based on the mechanical analysis when the fiber content is 15% wt, hemp fibers enhance the tensile and bending modulus of composite higher than the other samples. This study makes it possible to qualify the composite at 15% in fiber content as competitive candidate for the preparation and development of a new ecological insulating material with high added value and a low cost.

References

A

CC E

PT

ED

M

A

N

U

SC R

IP T

[1] Pickering, K. L., Efendy, M. A., and Le, T. M., 2016, "A review of recent developments in natural fibre composites and their mechanical performance," COMPOS PART A, 83, pp. 98-112. [2] Baley, C., 2002, "Analysis of the flax fibres tensile behaviour and analysis of the tensile stiffness increase," COMPOS PART A, 33(7), pp. 939-948. [3] Razak, S. I. A., Rahman, W. A. W. A., and Yahya, M. Y., 2014, "Hybrid composites of short acetylated kenaf bast fiber and conducting polyaniline nanowires in epoxy resin," J. Compos. Mater., 48(6), pp. 667-676. [4] Razak, S. I. A., Rahman, W. A. W. A., Hashim, S., and Yahya, M. Y., 2014, "Polyaniline and their conductive polymer blends: A short review," Malaysian Journal of Fundamental and Applied Sciences, 9(2). [5] Wambua, P., Ivens, J., and Verpoest, I., 2003, "Natural fibres: can they replace glass in fibre reinforced plastics?," Compos. Sci. Technol., 63(9), pp. 1259-1264. [6] Hadjadj, A., Jbara, O., Tara, A., Gilliot, M., Malek, F., Maafi, E. M., and Tighzert, L., 2016, "Effects of cellulose fiber content on physical properties of polyurethane based composites," Compos. Struct., 135, pp. 217-223. [7] Radzi, A., Sapuan, S., Jawaid, M., and Mansor, M., 2017, "Influence of fibre contents on mechanical and thermal properties of roselle fibre reinforced polyurethane composites," Fiber Polym, 18(7), pp. 1353-1358. [8] Oushabi, A., Sair, S., Abboud, Y., Tanane, O., and El Bouari, A., 2017, "An experimental investigation on morphological, mechanical and thermal properties of date palm particles reinforced polyurethane composites as new ecological insulating materials in building," Case Studies in Construction Materials. [9] Silva, M., Lopes, O., Colodette, J., Porto, A., Rieumont, J., Chaussy, D., Belgacem, M., and Silva, G., 2008, "Characterization of three non-product materials from a bleached eucalyptus kraft pulp mill, in view of valorising them as a source of cellulose fibres," Industrial Crops and Products, 27(3), pp. 288295. [10] Huber, T., and Müssig, J., 2008, "Fibre matrix adhesion of natural fibres cotton, flax and hemp in polymeric matrices analyzed with the single fibre fragmentation test," Compos. Interfaces, 15(2-3), pp. 335-349. [11] Haghighatnia, T., Abbasian, A., and Morshedian, J., 2017, "Hemp fiber reinforced thermoplastic polyurethane composite: An investigation in mechanical properties," Industrial Crops and Products, 108, pp. 853-863. [12] Otto, G. P., Moisés, M. P., Carvalho, G., Rinaldi, A. W., Garcia, J. C., Radovanovic, E., and Fávaro, S. L., 2017, "Mechanical properties of a polyurethane hybrid composite with natural lignocellulosic fibers," COMPOS PART B ENG, 110, pp. 459-465. [13] Sair, S., Oushabi, A., Kammouni, A., Tanane, O., Abboud, Y., Hassani, F. O., Laachachi, A., and El Bouari, A., 2017, "Effect of surface modification on morphological, mechanical and thermal conductivity of hemp fiber: Characterization of the interface of hemp–Polyurethane composite," Case Studies in Thermal Engineering, 10, pp. 550-559. [14] ASTM D 2842-01 "Standard Test Method for Moisture Absorption Properties and Equilibrium Conditioning of Polymer Matrix Composite Materials. [15] ASTMC177 "Standard Test Method for Steady-State HeatFlux Measurements and Thermal Transmission Properties by Means of the Guarded Hot-Plate Apparatus." [16] ASTM D638 "Standard Test Method for Tensile Properties of Plastics Apr 2008." [17] ASTM D-790 "Standard Test Methods for Flexural Properties of Unreinforced and Reinforced Plastics and Electrical Insulating Materials.." [18] Abdelmouleh, M., Boufi, S., ben Salah, A., Belgacem, M. N., and Gandini, A., 2002, "Interaction of silane coupling agents with cellulose," Langmuir, 18(8), pp. 3203-3208.

A

CC E

PT

ED

M

A

N

U

SC R

IP T

[19] Valadez-Gonzalez, A., Cervantes-Uc, J., Olayo, R., and Herrera-Franco, P., 1999, "Chemical modification of henequen fibers with an organosilane coupling agent," COMPOS PART B ENG, 30(3), pp. 321-331. [20] Chauhan, M., Gupta, M., Singh, B., Singh, A., and Gupta, V., 2014, "Effect of functionalized lignin on the properties of lignin–isocyanate prepolymer blends and composites," Eur. Polym. J., 52, pp. 3243. [21] Nies, C., Fug, F., Otto, C., and Possart, W., 2014, "Adhesion of polyurethanes on native metal surfaces–stability and the role of urea-like species," Int. J. Adhes. Adhes., 52, pp. 19-25. [22] Valério, A., Araújo, P. H., and Sayer, C., 2013, "Preparation of poly (urethane-urea) nanoparticles containing açaí oil by miniemulsion polymerization," Polímeros, 23(4), pp. 451-455. [23] Cinelli, P., Anguillesi, I., and Lazzeri, A., 2013, "Green synthesis of flexible polyurethane foams from liquefied lignin," Eur. Polym. J., 49(6), pp. 1174-1184. [24] Nacas, A., Ito, N., Sousa JR, R. D., Spinacé, M., and Dos Santos, D., 2017, "Effects of NCO: OH ratio on the mechanical properties and chemical structure of Kraft lignin–based polyurethane adhesive," The Journal of Adhesion, 93(1-2), pp. 18-29. [25] Huang, X., Alva, G., Jia, Y., and Fang, G., 2017, "Morphological characterization and applications of phase change materials in thermal energy storage: A review," Renewable and Sustainable Energy Reviews, 72, pp. 128-145. [26] Boukhattem, L., Boumhaout, M., Hamdi, H., Benhamou, B., and Nouh, F. A., 2017, "Moisture content influence on the thermal conductivity of insulating building materials made from date palm fibers mesh," CONSTR BUILD MATER, 148, pp. 811-823. [27] Espert, A., Vilaplana, F., and Karlsson, S., 2004, "Comparison of water absorption in natural cellulosic fibres from wood and one-year crops in polypropylene composites and its influence on their mechanical properties," COMPOS PART A, 35(11), pp. 1267-1276. [28] Dhakal, H., Zhang, Z., and Richardson, M., 2007, "Effect of water absorption on the mechanical properties of hemp fibre reinforced unsaturated polyester composites," Compos. Sci. Technol., 67(7), pp. 1674-1683. [29] Venkateshwaran, N., ElayaPerumal, A., Alavudeen, A., and Thiruchitrambalam, M., 2011, "Mechanical and water absorption behaviour of banana/sisal reinforced hybrid composites," Materials & Design, 32(7), pp. 4017-4021.

Tables list Table 1. Thermal conductivity of PU, HF and PU-HF composites.

Density (Kg/m3)

λ (W/m × K)

R (m2 × K/mW)

PU PU 5% PU10% PU15% PU20% PU25% PU30% T.F

32.46 36.02 38.44 41.08 41.76 45.29 48.09 ------

0.0306 ±0.0008 0.0339 ±0.0010 0.0348 ±0.0010 0.0372 ±0.0011 0.0381 ±0.0011 0.0395 ±0.0011 0.0407 ±0.0012 0.0480 ±0.0014

3.268 ± 0.100 2.950 ±0.088 2.874 ±0.086 2.868 ±0.086 2.625 ±0.079 2.532 ±0.076 2.457 ±0.074 2.083 ±0.062

SC R

IP T

Fiber content

Table 2. Water absorption behavior of polyurethane base resin and PU-HF composites

Percentages of water uptake at infinite time Ws %

Sorption coefficient S

Diffusion coefficient D (mm2/s)

Permeability coefficient P (mm2/s)

PU PU 5% PU10% PU15% PU20% PU25% PU30%

15.70 28.98 31.15 38.42 40.06 43.87 64.25

1.33 2.21 1.93 1.79 1.79 1.85 1.48

1.10.10-5 1.47.10-5 1.88.10-5 2.52.10-5 2.87.10-5 3.26.10-5 7.45.10-5

1.46.10-5 3.25.10-5 3.63.10-5 4.51.10-5 5.13.10-5 6.03.10-5 1.10.10-4

ED

M

A

N

U

Fiber content %

Table 3.Tensile properties of PU- HF composite at different fiber contents.

σ (MPa)

E (GPa)

PU PU 5% PU10% PU15% PU20% PU25% PU30%

1.029 ± 0.123 1.150 ± 0.138 1.206 ± 0.144 1.413 ± 0.168 1.182 ± 0.141 0.871 ± 0.104 0.675 ± 0.081

13.19 ± 3.08 13.21 ± 3.08 13.31 ± 3.10 14.42 ± 3.37 10.73 ± 2.50 9.26 ± 2.16 6.50 ± 1.52

A

CC E

PT

Fiber content

Table 4.Flexural properties of PU-HF composite at different fiber contents.

Fiber content

σ (MPa)

E (GPa)

PU PU 5% PU10% PU15% PU20% PU25% PU30%

1.09 ± 0.05 1.43 ± 0.07 1.86 ± 0.08 2.15 ± 0.13 3.83 ± 0.29 3.41 ± 0.25 2.61 ± 0.19

6.62 ± 3.08 8.73 ± 3.08 11.41 ± 3.10 12.66 ± 3.37 21.10 ± 1.52 19.54 ± 2.16 15.37 ± 2.50

SC R

IP T

Figures caption

PT

ED

M

A

N

U

Fig.1. Precursor for synthesis of PU-HF composite

A

CC E

Fig.2. Thermal Conductivity Analyzer (λ-Meter EP500e)

(a)

(b)

Fig.3: Tensile test machine (Instron MPK universal.) (a), Flexural test machine (3R_Quantium of 10kN load cell (b)

IP T SC R U N A M ED

A

CC E

PT

Fig.4. IR spectra of Hemp fiber, neat PU foam and PU-HF composites.

IP T SC R U N A M ED PT CC E A Fig.5.Thermal conductivity versus time of PU, H.F and PU-HF composites.

IP T

40

20

PU 0 0

1

2

3

4

5

6

7

SC R

% Moisture Absorption

60

PU5% PU10% PU20% PU25%

PU15% PU30%

8

13

9 1/2

11

12

14

N

U

Time in (Hrs)

10

M

A

Fig.6. Water absorption curves of polyurethane and PU-HF composites

45

ED

40 35

PT

20

CC E

Load (N)

30 25

PU PU5% PU10% PU15% PU20% PU25% PU30%

15 10

A

5 0

0

2

4

6

8

Deplacement (mm) Fig. 7.Tensile behavior of PU-HF composites.

10

15

IP T SC R U N A M ED PT CC E

Figure 8: Scanning electron micrographs for hemp fibers (D), hemp fibers covered by the PU

A

matrix (A), Polyurethane matrix (B) and composite at 30% in fiber content.