Flame Retardancy and Mechanical Properties of Thermal Plastic Composite Panels Made From Tetra Pak Waste and High-Density Polyethylene
Changyan Xu,1 Weicheng Jian,1 Cheng Xing,2 Handong Zhou,1 Yuqing Zhao,1 Hui Pan,1 Xueping Xiong3 1 College of Materials Science and Engineering, Nanjing Forestry University, Nanjing, Jiangsu 210037, People’s Republic of China 2
School of Packaging, Michigan State University, East Lansing, Michigan 48824
3
Hainan Kunlun New Material Science and Technology Co., Ltd, Haikou, Hainan 571127, People’s Republic of China
In this article, flame retardancy thermoplastic composites were developed by extrusion followed by injection molding using recycled Tetra Pak packaging material (TPP) waste and high-density polyethylene (HDPE) with addition of ammonium polyphosphate (APP) and melamine (MEL) as intumescent flame retardants (FRs). The influences of intumescent FRs on the properties of composites were investigated. FRs loading positively affected flame retardancy, but deteriorated mechanical properties as the loading rate was more than 30 wt%. Considering the fire retardancy and tensile strength (TS), the content of FR should not be more than 30 wt%. When the ratio of APP/MEL was less than 3/1, both combustion behavior and TS of the composites were improved with the increased FR loading, which was supported and verified by the analysis of FTIR spectra and SEM images. The thermogravimetric analysis results indicated that the incorporation APP and/or APP and MEL into composites as FRs into composites promoted char formation and correspondingly improved the thermal stability. The synergistic effect of APP and MEL in the intumescent FR system further improved the flame retardancy of the compoC 2014 Society sites. POLYM. COMPOS., 37:1797–1804, 2016. V of Plastics Engineers
INTRODUCTION The Tetra Pak packages, a good example of plastic multilayer packaging, are widely used in more than 170 countries around the world for packing many different goods, especially delicate foods such as milk, soy beverages, juice and nectars, and medical–hospital devices [1, 2]. According to the statistic figures of the Tetra PakV in 2013, there were 77,307 million liters of products sold with Tetra Pak packaging materials (TPPs), and a number of 173,234 million TPPs sold in 2012 [1]. Generally, Tetra Pak material consists of approximately 75% paperboard to provide stability, strength, and smoothness to the printing surface, 20% low-density polyethylene (LDPE) to barrier water vapor and enable the paperboard to stick to the aluminum foil (5%), which has excellent barrier properties for oxygen and light. This multilayer structure makes it difficult to recycle the used TPPs. Much attention has been paid to this issue, such as developing sustainable products, reducing environmental footprint across the value chain and increasing recycling [3]. The Tetra PakV states that it will aim to help double global recycling rate by 2020 to 40% within the whole recycling chain and has made many achievements. A recycling program for Tetra Pak cartons was introduced in Canada as early as 1990, and in 2000, the Tetra PakV invested e500,000 in its first recycling plant in Southeast Asia for aseptic packages. In 2010, 30 billion used Tetra Pak carton packages were recycled, a doubling since 2002, and in 2011, about 20% of Tetra Pak cartons were recycled globally, the countries like Belgium, Germany, Spain, and Norway showed local recycling rates of more than 50% [4]. However, it has been a new topic for China to recover and recycle the used paper/plastic/aluminum packages effectively and economically. The reclaiming R
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Correspondence to: C. Xu; e-mail:
[email protected] Contract grant sponsor: Jiangsu Overseas Research and Training Program for University Prominent Young and Middle-Aged Teachers and Presidents; contract grant sponsor: National Natural Science Foundation of China; contract grant number: 31300483; contract grant sponsor: Natural Science Foundation of Jiangsu Province of China; contract grant number: BK20130971; contract grant sponsor: Priority Academic Program Development of Jiangsu Higher Education Institutions (PAPD). DOI 10.1002/pc.23352 Published online in Wiley Online Library (wileyonlinelibrary.com). C 2014 Society of Plastics Engineers V
POLYMER COMPOSITES—2016
rate was less than 8% in 2008, and millions of TPPs were treated as rubbish by landfill and burning, resulting in a serious problem of resource waste and environmental pollution. Hydropulping technique, one of recycling proposals of the Tetra PakV, involves separation of paperboards from polyethylene (PE) and aluminum film and allow them to return to production chain as raw materials [2], but it has not been widely used in China because of water pollution. Thermally compressing technique, converting directly shredded cartons into bio-compositepanels, has been paid much attention [2, 5–7]. Nevertheless, limited shapes and structural inhomogeneity of such panels limit its wide application in China. Korkmaz gave another proposal, burning Tetra Pak waste for energy [8], but until now, Chinese companies have not accepted this technique. In recent years, the authors have tried to find some solutions of plastic multilayer packaging material waste accumulation problem. An electromagnetic shielding board has been made using Tetra Pak waste and metal fibers [9–12]. In this article, flame proofing composites were developed using Tetra Pak packaging waste and high-density polyethylene (HDPE) to add new members to the family of wood plastic composites (WPCs). WPCs represent a growing class of materials in furniture making, automotive components, packaging, and building because of their resistance to moisture, insects, decay, and warping; however, the flammable nature is becoming a major issue and limiting their applications. The most expeditious method used to acquire flame retardancy is incorporation of flame retardant (FR) that can interfere with combustion during a particular stage of the process so that the resulting system shows satisfactory flame retardancy [13]. In recent years, intumescent FR systems, which generate little smoke and no corrosive gas during combustion, have been made to substitute halogenated FR systems, which produce high toxic products of thermal decomposition [14–18]. Garcıa [19] and Stark [20] believed that the combination of charring cellulosic material and intumescent system could lead to an optimized FR formulation of WPCs. Generally, the formulation of intumescent FR consists of an acid source, a blowing agent and a carbonific agent. Ammonium polyphosphate (APP), melamine (MEL), and pentaerythritol are traditionally used as the three parts, respectively. During combustion, both MEL and APP can act as phosphorous nitrogen synergism; MEL creates endothermic reactions and scavenges free radicals; aids in formation of protective cellular char and then inhibits access to oxygen; and APP intumesces, lowers smoke production and inhibits smoldering [14]. Therefore, the aim of this article is to develop an environmentally friendly and valueadded WPC with satisfactory flame retardancy using recycled TPPs and intumescent FR systems. TPP was used as carbonific agent, considering that it contains about 75% paperboard, which has more cellulose than wood powder; APP and MEL were used as acid source R
1798 POLYMER COMPOSITES—2016
and blowing agent, respectively. The flammability, thermal stability, and mechanical properties of the composites were evaluated. EXPERIMENTAL Materials HDPE was purchased from Sinopec. as a virgin material (HDPE 5000s, with melt flow index of 1.0 g/10 min, density of 0.951g/cm3, elongation ratio of 500%, and yielding tensile stress of 23.0 MPa). Recycled TPPs were collected from municipal solid waste in Nanjing, China. After cleaning with water and air drying, they were broken into size of 2–3 3 6–7 mm with a L-905 shredder, then grinded into powders with a FZ102 miniature plant grinder (TAISITE instrument Co., Tianjin) and sieved with a 20–100 mesh standard sieve (Zhang Xing Sand Screen Factory, Zhejiang province) to get powder with size of 20–40 mesh (380–830 lm). After drying in a DHG-9070A oven at 110 C for about 8 h, the powder with 2–3% moisture content was obtained. Additive consisting of maleic anhydride grafted polyethylene (PEMA) (with grafting ratio of 0.9%, a melt index of 0.9 g/10 min, density of 0.92 g/cm3) and fatty acid metal soap was provided by Hainan Kunlun Wood Industry Co. The intumescent FR system was based on APP and/or MEL. APP, with a polymerization degree of more than 1,500, density of 1.951 g/cm3, decomposition temperature of more than 275 C, PH of 7.1, and diameter of 16 lm, was supplied by Zhenjiang Xingxing Flame Retardant Co., MEL (KT-12B), with melting point of more than 300 C, density of 1.573 g/cm3, saturated vapor pressure of 6.66 KPa, and solubility in water of 0.33 g (20 C), was kindly provided by Tianjin Hengxing Chemical Preparation Co. Composite Fabrication In all fabricated composites, TPP, HDPE, and additives were first dry blended at a fixed rate of 70, 26, and 4 wt% (3% MAPE and 1% fatty acid metal soap), respectively. Then amounts of FRs were added into the premixture to obtain the designed FRs ratio (based on the weight of premixture) as listed in Table 1. To show the effect of APP on the composites, five formulations coded as A1– A5 in the first group were used, and A0 without any FR was the control. F1–F4 in the second group were used to evaluate the synergic effect of APP and MEL at the fixed loading rate (30 wt%, based on the weight of the premixture) with different APP/MEL mixing ratios (1/1 to 4/1). The third group, B1–B5, was used to investigate the effects of loading rate on the flame retardancy at a fixed APP/MEL mixing ratio of 3/1. The premixure and the FRs were blended with a plastic mixer (SHR-10A, Zhangjiagang Zhenxiong Plastic Machinery Company, China) at 85 rpm for 5 min to obtain homogeneous physical blends. After blending, the DOI 10.1002/pc
TABLE 1.
Formulations of the FR system.
Group code
Formulation code
APP loading (%wt)
MEL loading (%wt)
Total FRs loading (%wt)
Control 1
A0 A1 A2 A3 A4 A5 F1 F2 F3 F4 B1 B2 B3 B4 B5
0 10 20 30 40 50 15 20 22.5 24 7.5 15 22.530 30 37.5
0 0 0 0 0 0 15 10 7.5 6 2.5 5 7.5 10 12.5
0 10 20 30 40 50 30 30 30 30 10 20 30 40 50
2
3
mixtures were compounded and palletized in a co-rotating double screw extruder (SHJ 20B, Nanjing Jie Ente ElecMech Limited Corp., China) with a length/diameter ratio of 40 at a screw speed of 250 rpm and a temperature profile of 155, 160, 165, and 170 C for the four zones. Then the pellets, with a good enough compatibility level between the phases together with a homogeneous fiber distribution, were dried overnight at 75 C, and were injected into molds with a Haitian HTF160X 60-ton injection molding machine (CWI-90BII, APOLLO Mechanical Industry, Hong kong) to produce test specimens for flammability and mechanical tests. The nozzle size was 10 3 4.5 mm, and the temperature and injection pressure was set at 170 C and 130 MPa, respectively. Flammability Testing Flammability of the composites was evaluated by limiting oxygen index (LOI) test according to ISO 4589-1:1996 and ISO 4589-2:1996, and vertical burn test according to IEC 60695-11-10:1999. LOI samples were tested on XZT100 Oxygen index measuring instrument (Chende Instrument Co.) at room temperature. In this test, a sample with a nominal dimension of 130 3 10.0 3 4.5 mm3 (length 3 width 3 thickness) as injection molded, was held vertically inside a closed glass chamber. The top end of the sample was ignited and the time to burn 50 mm of the sample length was measured. The test was repeated under various concentrations of O2 and N2 to determine the minimum concentration of O2 needed to sustain burning, which is called oxygen index (OI) and expressed as a percentage of O2/N2 in atmosphere. At least five specimens for each composite were tested, and the OI results were recorded. In the vertical burn test, five specimens of each composite with dimensions of 13.0 3 4.5 3 130 mm3 (length 3 width 3 thickness) were firstly controlled at 23 6 2 C and 50 6 5% relative humidity for 48 h, and then suspended vertically by clamps (6 mm length). The distance DOI 10.1002/pc
between the sample’s bottom surface and the horizontal absorbent cotton layer was 300 mm. A flame fuelled by a Bunsen burner was applied to light the center region of the sample’s bottom surface. After lighting 10 s, the lighting flame was moved away and the afterflame time was measured. After the flame died out, a flame was applied to light the same area again for 10 s, and the afterflame time and afterglow time (blazing but no flame) were measured. Table 2 listed the discriminating criteria. Mechanical Property The mechanical property was evaluated by tensile strength (TS). The TS test was conducted at room temperature (23 C) with a CMT 4204 testing machine (SANS, Sans Materials Testing Co., China) in accordance with ASTM D 638 at a crosshead speed of 5 mm/min. Specimen dimension was 100.0 3 10.0 3 4.5 mm3 (length 3 width 3 thickness). In all cases, the average values of three specimens were taken for each sample. Thermo Gravimetric Analysis Thermo gravimetric analysis of the composites was studied on a TGAQ5000 thermo gravimetric analyzer (NETZSCH-Ger€atebau GmbH, German) from room temperature to 800 C using heating ramp of 20 C/min in a N2 environment (20 mL/min). A sample of 5 mg was used for each run. SEM Analysis After drying at 60 C for 8 h, the surfaces of combustion resides were coated with 2 nm platinum layer by an ion sputter coater (SCD-500, BAL-TEC, Germany), and then analyzed with a SEM machine (JSM-7600F, Japan) at a working distance of 25 mm. The accelerating voltage was 3 kV. FTIR Analysis FTIR analysis was performed using a Nicolet IS10 spectrophotometer (Thermo Scientific, America) equipped TABLE 2. Vertical flame test discriminating criteria. Grades (V: vertical) Burning characteristics
V-0
V-1
V-2
Each sample’s afterflame time after being lighted every time was not more than (s) Afterflame time of samples after being lighted for 10 times was not more than (s) Each sample’s afterglow time after being lighted in the second time (s) Flame-spreading into the clamp during afterflame or afterglow for each sample Igniting the absorbent cotton layer by the drop for each sample
10
30
30
50
250
250
30
60
60
No
No
No
No
No
Yes
POLYMER COMPOSITES—2016 1799
TABLE 3. Properties of the composites. Formulation A0 A1 A2 A3 A4 A5 F1 F2 F3 F4 B1 B2 B3 B4 B5
OI (%)
FR grade
TS (MPa)
19.1 6 1.51 21.4 6 1.76 24.9 6 1.31 26.6 6 1.21 28.2 6 1.13 29.6 6 1.39 26.4 6 0.77 27.1 6 1.33 28.1 6 1.62 26.8 6 2.18 21.8 6 1.46 25.1 6 1.68 28.1 6 0.76 29.3 6 1.54 31.2 6 1.63
Flammable Flammable V-2 V-1 V-0 V-0 V-1 V-0 V-0 V-0 Flammable V-2 V-0 V-0 V-0
25.14 6 1.69 22.14 6 1.69 21.94 6 1.40 20.43 6 0.75 18.52 6 0.64 17.38 6 1.29 17.57 6 1.15 18.85 6 1.61 19.23 6 0.87 19.61 6 1.29 20.87 6 2.04 19.61 6 2.01 19.23 6 0.53 18.12 6 1.30 16.80 6 0.88
The data after symbol 6 are standard deviation.
with a single reflection attenuated total reflectance system to monitor the degradation of different compounds on heating. Each sample consisted of 100 scans in absorbance units from 4,000 to 500 cm21, and the resolution was 4 cm21. RESULTS AND DISCUSSION Effects of APP Loading on the Properties of the Composites In Table 3, A0–A5 showed the effect of APP loading on the flame retardancy of the composites with APP as FR. In the vertical flame test, A0 and A1 burned with a large flame accompanying pungent smoke and melt dripping, which ignited the cotton layers beneath the burning specimens, and smoldered after the flame died out. All these characteristics indicate A0 and A1 are flammable materials. The flame of A2–A5 was getting smaller and smaller gradually and self extinguished; the smoke was less than those of A0 and A1 and no melt dripping exception of A2 was observed from the burning samples. Especially, A4 and A5 expanded obviously because of gas evolving and emitting from the inside of the sample to the outside and formed char on the surfaces, which exhibited flame self-extinguishment. According to the discriminating criteria in Table 2, A2 was classified as “V-2”, A3 classified as “V-1”, and A4 and A5 classified as “V-0”. The OI testing results also showed that the flame retardancy of the composites only using APP as FR was positively affected by APP loading. APP, an intumescent material, foams and creates an expanded shield on the composite surface, which blocks heat and oxygen from the flammable surface, improving charring in a heated environment [21]. A continuous char layer on the surface could be formed as APP loading increases to a certain level and to limit the spread of fire. The effect of APP loading on the flame retardancy of the composites with APP as FR was also supported by 1800 POLYMER COMPOSITES—2016
SEM images of A0, A2, and A5, as shown in Fig. 121, 122, and 123. The char residue of A0 had little expanded shield on the surface, resulting in poor flame retardancy. In addition, compared with A2, the residue of A5 presented a more continuous and compact charring layer, which blocked heat and oxygen from the flammable surface, resulting in better flame retardancy performance. For the samples of A1–A5 in Table 3, the TS decreased significantly from 25.14 to 17.38 MPa as APP loading increased from 0 to 50 wt%. The deterioration of mechanical properties with high content of APP in the composites was attributed to the poor interaction and compatibility between APP and Tetra Pak and HDPE [18]. Synergism Effect of FRs on the Properties of Composites In the vertical flame test, F1 and F2–F4 presented similar combustion characteristics as A3 and A4, respectively, resulting in their classifications as “V-1” and “V-0” as shown in Tables 2 and 3. This result was also consistent with the OI testing results. The OI increased from 26.4 to 28.1% as the mixing ratio of APP/MEL increasing from 1/1 to 3/1, and then decreased to 26.8% with further increasing the ratio to 4/1, demonstrating that for an intumescent FR system at 30 wt% loading rate of FR, the mixing ratio of APP/MEL affected positively flame retardancy of the composites at a lower level, but conversely at a higher level, the threshold was 3/1. Researches showed that only phosphorous did not increase char in polyolefins unless there was another char forming additive present, typically a nitrogen containing compounds [22]. MEL used in the test compounded with APP to achieve a synergism system, assisting flame retardance in several ways, while decomposing. MEL creates endothermic reactions and scavenges free radicals, and its decomposition produces N2 and NH3, which dilutes fuel gases; and it also could help in char formation [21]. However, too much MEL as gas source also causes too much emission of NH3 quickly, resulting in breakage of the complete shielding charring layer, which increases transferring speed to the flame zone of degradation products and makes heat flow from the outside to the inside more easily [23]. These discussions can be verified by the analysis of FTIR spectra and SEM images in this test as follows. TS of the composites increased from 17.57 to 19.61 MPa as APP/MEL mixing ratio increasing from 1/1 to 4/ 1. This improvement of TS could be attributed to the low molecular weight of MEL, which not only cannot play the reinforcing function as filler, but also can weaken the intermolecular force of PE. FTIR Spectra of the Samples With Different Mixing Ratio of APP/MEL FTIR spectra of A0 and F3 before and after combustion were shown in Fig. 2. Compared with that of A0, the DOI 10.1002/pc
FIG. 1.
SEM images of char residues of the samples.
spectra of F3 before combustion presented three main differences as shown in Fig. 2-1. The first was the typical vibration (760 cm21) of APP, and the second was the typical stretching vibration (810 cm21) of three triazine rings, contained in nitrogen-containing heterocyclic organic compounds [24]. The last one was C@O stretching vibration of carboxylic group (1,675 cm21), due to acetic acid evolution caused by the reaction of MEL and maleic anhydride grafted polyethylene (PE-g-MAH) [25]. These three characteristics along with the presence of HDPE made the linear structure of macromolecular chains become cross-linked network, which increased char yield at starting of combustion. After combustion (Fig. 2-2), the spectrum of residues of F3 showed four vibrations in 1,680, 1,429, 1,065, and 910 cm21, respectively. The peaks in 1,680 and 1,429 cm21 represent the stretching vibration of polynuclear aromatic ring in the char with phosphorus compounds and the bending vibration of NAH contained in NH 1 4 . The vibration peaks in 1,065 and 910 cm21 belong to PAOAC and P@O in the evolving H3OP4 and HOP3 [26, 27]. In a Tetra Pak/HDPE/APP/MEL system, P, O, and C are linked mainly by C@O, PAOAC, P@O during combustion. APP will decompose and produce H3OP4 and NH3 upon being heated at first, and then the H3OP4 continues to decompose into sulfite and water vapor [14], and the DOI 10.1002/pc
NH3 and water vapor can dilute fuel gases. At the same time, the H3OP4 melts and covers the surface of the composite fiber to form a char layer, which blocks heat and oxygen from the flammable surface. In addition, the evolved P@N bond caused by decomposition can react with hydroxyl groups of cellulose resulting in cellulose phosphorylation, which would continue to lose amine and generating P@O bond, and finally become amorphous carbon. Moreover, the decomposition of MEL also produces non combustible gases, such as N2 and NH3, which would not only take away a lot of heat and reduce the oxygen content from the burning surface, but also fill inside the charring layer, resulting in an expanded charring one. The difference of FITR curves of A5 and B5 (Fig. 2-3 and Fig. 2-4) also confirmed the above evolving function groups. Just like that of F3, the curve of B5 presented a peak in 810 cm21 and a peak in 1,675 cm21 before combustion. In addition to, it had much stronger vibration peaks in 2,915 and 2,850 cm21, which was the symmetry and asymmetry vibration absorption of aliphatic hydrocarbon in evolving char layers, respectively. These new functional group in B5, produced in the reaction of MEL and PE-g-MAH, made polymer chains link together and form a denser and stronger charring layer to block the melt polymer composites from further combustion, and then left more aliphatic hydrocarbon in the residues. POLYMER COMPOSITES—2016 1801
FIG. 2. FITR spectra of samples with different ratio of APP/MEL.
SEM Images of Samples With Different Mixing Ratio of APP/MEL The synergism of APP and MEL in an intumescent FR system was also verified by the SEM images of F1 (ratio of APP/ MEL was 1/1) and F3 (ratio of APP/MEL was 3/1) shown in Fig. 1-4 and 1-5. Compared with that of F1, the image of F3 showed a more continuous and compact thick charring layer, which helped block heat and oxygen from the flammable surface, resulting in a better flame retardancy performance. So, in a heated environment, it is appropriate for a higher ratio of APP/MEL with regard to the synergistic effect on the flame retardancy performance of composites.
supported by the analysis of SEM images of B2 and B5, shown in Fig. 1-6 and 1-7. Compared to B2, B5 had a more continuous and compact thick charring layer and with fewer holes on the charring surfaces. For B2, the amount of APP and MEL was too low to release enough noncombustible gas, resulting in a “V-2” classification. Contrarily, the TS deteriorated by the increasing APP/ MEL content, especially as FR content was more than 30 wt% as shown in Table 3. So, a conclusion could be drawn that for the Tetra Pak and HDPE system with APP and MEL as intumescent FR, the threshold of mixing ratio of APP/MEL was 3/1, and the content of APP and MEL should be 30 wt%. Effects of FRs on TGA of the Composites
Effects of APP/MEL Loading on Properties of the Composites In Table 3, when the ratio of APP/MEL in the intumescent FR system was 3/1, the OI increased from 21.8 to 31.2 as the content of FRs increased from 10 to 50 wt%. The flame retardancy classification levels from the vertical test were also increased gradually from flammable (B1) to V-2 (B2) and V-0 (B3–B5). This result was 1802 POLYMER COMPOSITES—2016
Figure 3 showed TGA curves of the composites, and Table 4 summarized the related data. On the basis of 5% mass loss, A0 without any FR showed the highest thermal stability because of a high initial temperature (T5%) of 303 C; and this initial temperature decreased with increasing FR loading in A3 and A5. In the initial decomposition period, the mass loss was mainly caused by evolution of water as reported in the literature and the DOI 10.1002/pc
FIG. 3. TG and TGA curves for A0, A3, B3, and A5 in an oxidative atmosphere (heating rate 20 C/min).
ces can promote dehydration of the cellulose in TPPs, and then speeded the build-up of carbon foam (char) on the composite surface against the heat source (charring). The carbon foam acts as an insulation layer and prevents volatile, combustible gases or further decomposition of the material. The main decomposition of the composites occurred at 440–510 C due to the decomposition of FR and PE. With increasing temperature, the evolved H3PO4 and HPO3 react with hydroxyl or other groups of a synergist to form an unstable phosphate ester, which dehydrated and resulted in carbon foaming on the surface against the heat source. When the temperature got up to 560 C, the decomposition tended to be stable, and the char residues of A3, B3, and A5 were over 30%, suggesting the excellent charring ability of the system. Compared with A0 and A3, A5 presented the lowest initial temperature (T5%) and the highest amount of char residues, meaning that more APP incorporated into the composites can significantly improve charring ability of the composites, and correspondingly increase the fire retardancy. Moreover, B3 had a same initial decomposition temperature (T5%), a higher temperature with 50 wt% mass loss (T50%), a higher peak with the largest decomposing rate (Rpeak1) and (Rpeak2), and a higher char residues amount at 700 C compared to A3, indicating that APP improved the fire retardancy and the synergistic of APP and MEL further enforced the fire retardancy of the composites.
decomposition of small molecules [14, 28]. After this, A0 showed a two-step decomposition curve. The first was at 303–442 C with a peak temperature of 350 C (T1peak) and a mass loss of 31.6 wt%, due to degradation of cellulose in TPPs, and the second was at 442–508 C with a peak temperature of 487 C (T2peak) and a mass loss of 12.6 wt%, caused by composition of HDPE in the matrix. Compared to A0, the incorporation of 30 wt% APP into A3, or 15 wt% APP and 15 wt% MEL into B3 improved the thermal stability (T2peak) of the composite from 487 to 497 C or 489 C, respectively, and enhanced the temperature T50% (on the basis of 50% mass loss) from 481 to 485 C or 494 C, respectively. It indicated that APP and/ or MEL change the thermal degradation behavior of the composites and promoted char formation and thereby delayed the degradation of TPP/PE. In addition, both A3 and B3 presented the same second decomposing period at 272–440 C, and the largest mass loss at 320 and 297 C and were lower than that of A0. Char formation is a basic aspect of FRs because the char reduces the combustion rate of polymeric materials by not allowing O2 to easily reach the combustion zone [18, 29]. When the system was exposed to an accidental fire or heat, the FR started to decompose at 190–300 C into H3PO4, HPO3, and NH3, which was related to acidic site formation involved in the intumescence phenomena [14]. The decomposing temperature of APP and MEL is a little lower than that of TPPs, and the evolved acidic substan-
TABLE 4. Thermal degradation and char residue data by TGA. Sample code A0 A3 B3 A5
T5% ( C)
T50% ( C)
Rpeak1 (%/min)
Tpeak1 ( C)
Rpeak2 (%/min)
Tpeak2 ( C)
Char residue at 700 C (%)
303 272 273 264
481 485 494 498
0.36 0.28 0.49 0.30
350 320 298 288
1.45 0.76 1.11 0.71
487 497 489 492
14.2 30.5 31.6 36.6
T5%, temperature at the mass loss of 5%; T50%, temperature at the mass loss of 50%; Tpeak1, temperature at the first peak; Rpeak1, mass loss rate at the first peak; Tpeak2, temperature at the second peak; Rpeak2, mass loss rate at the second peak.
DOI 10.1002/pc
POLYMER COMPOSITES—2016 1803
CONCLUSIONS Composites with adequate flame retardancy and TS were developed using Tetra Paks waste and HDPE with addition of fire retardants. FR loading positively affected the fire retardancy of the composites, but deteriorated the TS as FR in the composites was more than 30%. Considering the fire retardancy and TS, the content of FR should not be more than 30 wt%. The APP and MEL as intumescent FRs presented a significant synergism effect on the properties of the composite. When the ratio of APP/MEL was less than 3/1, both combustion behavior and TS of the composites were improved with the increased FR loading, which was supported and verified by the analysis of FTIR spectra and SEM images. In addition, the TGA study indicated that the incorporation APP and/or APP and MEL into composites as FRs promoted char formation and correspondingly improved the thermal stabilityand the synergistic of APP and MEL in the intumescent FR system further enforced the flame retardancy of the composites. REFERENCES 1. Available at: http://www.tetrapak.com/about-tetra-pak/thecompany/facts-and-figures. Figures. 2013-12-31. 2. C.M.A. Lopes and M.I. Felisberti, J. Appl. Polym. Sci., 101, 3183 (2006). 3. Available at: http://www.tetrapak.com/about-tetra-pak/pressroom/news/progress-towards-environmental-targets. 2014-03-06. 4. Available at: http://www.answers.com/topic/tetra-pak#Recycling. 2014-06-18. 5. C.Y. Xu, X.D. Zhu, and J. Liu, China Patent ZL 2011 1 0028554.9 (2012). 6. G.S. Hwang, E.I.C. Wang, and Y.C. Su, J. Wood Sci., 1, 6 (2006). 7. N. Ayrilmis, Z. Candan, and S. Hiziroglu, Mater. Des., 29, 1897 (2008). 8. A. Korkmaz J. Yanik, M. Brebu, and C. Vasile, Waste Manage., 29, 2836 (2009). 9. C.Y. Xu, J. Liu, X.D. Zhu, Y.L. Zhu, X.P. Xiong, and C. Xing, J. Mater. Cycles Waste Manage., (2014), doi: 10.1007/s10163-014-0255-9.
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DOI 10.1002/pc
