Study on blending modification of waste flame-retardant HIPS plastic

Transcription

1 Study on blending modification of waste flame-retardant HIPS plastic Yuan CHEN 1, Ya-lin HU, Lie-qiang CHEN, Jin-hui LI 1 1Department of Environmental Science and Engineering, Tsinghua University, 84, Beijing, China Chemistry and Chemical Engineering Department, South China University of Technology, 564, Guangzhou, China chenyhr@mail.tsinghua.edu.cn Abstract: Physical modification was used in recycling of waste flame retarded HIPS (high impact polystyrene) plastics. Styrene butadiene rubber (SBR) and styrene-butadiene-styrene copolymer (SBS) being used as flexibilizer to toughen waste HIPS plastics was studied and the mechanical properties of modified plastic were analyzed in the experiment. The results showed that when the addition of SBS or SBR was % or 3%, the modified plastics had the maximum izod impact strength of KJ/m and KJ/m respectively, which increased 96.3% and 66.8%. Based on the optimal toughening formula, the influence of nano-organic montmorillonite (OMMT) on mechanical properties of modified plastic were studied further. The results showed that when the addition of OMMT was 6%, the mechanical properties enhanced notably. Key words: waste HIPS plastic; blending modification; rubber elastomer; OMMT 1. Introduction High impact polystyrene (HIPS) mainly used in electrical and electronic equipment (EEE) is one kind of Polystyrene(PS). The consumption of HIPS In EEE plastics is about 56%. Once the EEE is written off, a large amount of waste HIPS plastics produced. Sound reuse of the waste HIPS plastics can both save natural resource and alleviate environmental pollution. Three methods of recycling waste plastics are safe landfill, incineration and reuse. The disposal of waste plastics in landfill site or their incineration creates a number of environmental problems, because they contain some additives such as heavy metals and halogenated flame retardants, which are hazardous for environment. Mechanical recycling is one of the best alternatives to treat WEEE plastics because the secondary environmental pollution avoided and natural source saved, which is the development prospects of recycling waste plastics [1]. Here we report the blending modification of HIPS plastics containing decabromodiphenyl ether with rubber elastomer (SBS and SBR) and OMMT. The effect of modifiers addition on the mechanical and flame-retardant properties of modified plastics was discussed.. Experimental section.1. Experimental materials Waste HIPS plastics were purchased from GuiYu in Guangdong province, which are fromtv shells and crushed into particles with diameter of about 5mm for experiment. Elemental analysis results are shown in table 1. SBS from BaLin Petrochemical Company, SBR and PS from QiLu Petrochemical Industrial Corporation Ltd., stearic acid from Guangzhou Panyu Strong Chemical Plant, antioxidant from Ciba Specialty Chemicals Ltd., OMMT with diameter 3.8nm, from Zhejiang Fenghong Clay Chemical Ltd. Table 1. Elemental analysis of waste TV plastic shells Element C H N S Br Content/% Instruments The main instruments used in the experiment are plastic workstation from German Brabender company, desk-top electronic material testing system from USA Instron company, scanning electron microscope from HITACHI, transmission electron microscope from Japan

2 electron company..3. Material formula [-4] The addition of every material in formula is shown in table and table 3. Table. Toughening formula table(unit: g) material Waste HIPS PS SBR 3 4 SBS 3 4 Stearic acid antioxidant Table 3. Formula table of modification with OMMT (unit: g) material Waste HIPS PS SBS OMMT Stearic acid antioxidant.4. Experimental procedure According to table or table 3, every material was weighed with the total weight of g. After being mixed through, the materials were melt blending and extrusion graining with twin-screw extruder. Grains were dried at 8 for h and then made into special shape for test. increased with the flexibilizer addition increasing. The main reason is that rubber elastomer has smaller tensile strength than HIPS plastics. 3. Results and discussion 3.1. Toughening modification with SBR and SBS Effect of flexibilizer addition on the tensile properties of Effect of flexibilizer addition on the tensile strength of is shown in figure 1. It can be seen that the tensile strength of decreased with the flexibilizer addition increase. The reduction range of Figure 1. Effect on the tensile strength of the modified with SBS was bigger than that with SBR. On the contrary, the elongation of

3 Figure. Effect on the elongation of the Effect of flexibilizer addition on the impact properties of Bending properties usually include bending strength and bending modulus. Because the bending properties of flexibilizer are lower than that of waste HIPS plastics, both the bending strength and bending modulus of decrease with the addition of flexibilizer increase (figure 4 and figure 5). Comparing to SBR, SBS has lesser influence on the bending properties of than SBR does. The main reason is that the structure of SBS is similar to that of HIPS, so they have good compatibility and the dispersed particles and the matrix have good interfacial adhesion. Figure 3. Effect on the impact strength of the Impact strength first increased and then decreased with the increase of flexibilizer addition (figure 3). When the addition of SBS is %, the impact strength reaches the maxum of kj/m. Comparing to that of waste HIPS, the increase range is 96.3%. But when SBR addition is 3%, the impact strength reaches the maxum of kj/m, and the increase range is 66.8%. Except for the change of test results, some experimental phenomena can interpret the increase of toughness of modified HIPS plastics. For example, during tensile process of, a large amount of craze appeared and the fractured surface was rough. However, during tensile process of waste HIPS plastic, the craze was little and the fractured surface was smooth Effect of flexibilizer addition on the bending properties of Figure 4. Effect on the bending strength of the Figure 5. Effect on the bending modulus of the SEM images of the The fractured surface of waste HIPS took on typical brittle fracture features, smooth having many slim and straight lines and having little crack(figure 6(a)). But the fractured surface

4 of became very rough, the cracks disappeared, and the fish scale appeared, which are the typical ductile fracture features. The main reason is that when the impacted by external force, flexibilizer particles act as focal point of stress, so a large amount of craze arises. Meanwhile, the particles can prevent the craze from unlimited growth. The stability of one craze can permit the other craze produce. The crazing process consumes a lot of energy, so the toughness and the impact strength of the increase. From the comparison between (b) and (b-1) or (c) and (c-1), we can see the fracture surface of the modified with SBR of 3% addition is rougher than that modified with SBR of 4% addition. The same experimental phenomena appeared on the modified with SBS. Too much flexibilizer leads to produce more blends defects and to disperse the flexibilizer particles into smaller ones which have no toughening function, so the impact strength declines accordingly. (a)waste TV shells (b) Modified with 3% SBR (b-1) Modified with 4% SBR (c) Modified with % SBS (c-1) Modified with 4% SBS Figure 6. SEM images of the different 3.. Modification of with OMMT The results of toughening modification of waste HIPS showed that SBS had better toughening effects than SBR did. And the mechanical properties of are the best when the addition of SBS is %. Therefore, taking the modified with SBS of % as experimental sample, we developed the studies of effects of OMMT on mechanical and flame-retardant properties of the Effect of OMMT addition on the mechanical properties of (1) Effect of OMMT addition on the tensile properties of The tensile strength of the increased and then decreased with the OMMT addition increase (figure 7). When the addition of OMMT is 4%, the tensile strength of the reaches the max, which is 3.7MPa. When the addition of OMMT is less than 4%, the OMMT particles disperse even in plastic

5 matrix and have strong interaction with the matrix [5]. However, when the addition is more than 4%, tensile strength of the decrease because of the aggregation of OMMT particles and occurrence of focal points of stress. As for elongation, it decreased with the OMMT addition increase (figure 8), the main reason is that the OMMT is rigid particles. Figure 7. Effect on the tensile strength of the Izod impact strength of the increased and then decreased with the OMMT addition increase. When the OMMT addition is 6%, the impact strength is maximum 16.KJ/m. Thus, small amount of OMMT can play the role of toughening. Once the addition of OMMT in exceeds 6%, the aggregation of OMMT particles leads to material crack under impact stress. (3) Effect of OMMT addition on the bending properties of OMMT particles act as physical crosslinking points in [6], when the addition is low (less than 6% here), they can be peeled or fully embedded to the matrix. Therefore the thin OMMT slice can enhance the mechanical property of the composite along two-dimensional direction, and the bending strength increased with the addition of OMMT increase accordingly (Figure ). However, if the addition increased continually, some OMMT particles will exist in their original state, and others will aggregate. Thus, the interaction between OMMT and plastic molecular chains weakened, which cause the bending strength decrease and the bending modulus leveled off (figure 11). Figure 8. Effect on the elongation of the () Effect of OMMT addition on the impact properties of Figure. Effect on the bending strength of the Figure 9. Effect on Izod impact strength of the

6 Figure 11. Effect on the bending modulus of the 3... SEM and TEM images of the Fracture surface of the without OMMT is rough (figure 1(a)) and has chip scale, but when modified with OMMT, the surface is much rougher and petal structure appeared(figure 1(a-1) and (a-)). Compared to the modified with 8% OMMT, the petal shape on fracture surface of the modified with 6% OMMT is more regular. The phenomenon further confirmed the aggregation of OMMT particles as shown in figure 13. (a) SBS% (a-1) SBS% OMMT6% (a-) SBS% OMMT8% Figure 1. SEM images of the (a) SBS% OMMT6% (b) SBS% OMMT8% Figure 13. TEM images of the 4. Conclusions As flexibilizer, SBR and SBS can increase izod impact strength of waste HIPS plastics, and SBS has more remarkable effects than SBR does. When the addition of SBR is %, the izod impact strength of increases from 7.11 KJ/m to KJ/m, the increase range is 96.3%; Based on the formula of NO.8, further studies that the effect of different OMMT addition(%,4%,6% and 8%) on the mechanical and flame-retardant properties of were made. The results showed that OMMT can increase the mechanical properties of to a certain degree, it is agree with the result in literature [7] and the addition of 6% is optimum. References

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