ABSTRACT

In general, high mechanical properties such as higher impact strength and thermal resistance are required for injection molded applications. Recycled PET (RPET) is well known to exhibit brittle behavior in the presence of notches and indicated the low heat distortion temperature. Therefore, we tried to improve the toughness and thermal resistance properties of RPET by incorporating E-GMA, talc filler and engineering plastics as an impact modifier and talc to increase the rigidity and heat distortion temperature of RPET. As a result, these blends with E-GMA exhibited significantly higher stiffness and strength especially with increasing E-GMA content. In addition, these blends with talc filler indicated the high heat distortion temperature due to the increase of the crystalinity of RPET blends. Therefore, it was found that talc played an important role in enhancing the heat resistance of RPET.

1. Introduction

Polyethylene terephthalate (PET) is widely used for synthetic fiber, beverage, food and other liquid container and so on, which constitutes a large portion of post consumer wastes. In the present day, the volume of the PET bottle products greatly increased. For example, the annual volume of consumption of PET drinking bottle in Japan [1] was 338,654 tons in 2000. However, in 2008, a 50% increase in volume to 520,120 tons was recorded. Therefore, recycling of PET bottles offers a very practical solution to reduce landfill waste thus preventing environmental problems. Indeed, there are some researches [2-7] about recycled PET (RPET) injection moldings from PET bottles.

Neat PET is known to possess high elastic modulus, strength and toughness. However, recycled PET (RPET) is more susceptible to impact loadings and have lower heat distortion resistance. In order to enhance its toughness, impact modifiers are often incorporated into RPET. In our previous work, the notched impact resistance of RPET was significantly enhanced when a polyethyl-eneglycidyl-methacrylate (E-GMA) based impact modifier was incorporated [6]. However, this led to deterioration in stiffness and yield strength of the material. Furthermore, the material would deform easily even when exposed to temperatures of around 50˚C. In order to improve the stiffness and heat distortion resistance of the material, talc, which is a popular mineral filler typically used with polypropylene, was incorporated into RPET in this study. In addition, RPET blends with polybutylene-terephthalate (PBT) were prepared in order to elucidate the effect of talc filler as a nucleation of crystallization. The effects of talc loading on the heat distortion temperature, fracture behavior and static and dynamic mechanical performance of the composites were elucidated.

2. Experimental

2.1. Materials

Recycled poly (ethylene terephthalate) (RPET) was supplied by Utsumi-Recycled-Systems Co. Ltd., Japan, which a waste management company, while the polyeth-yleneglycidyl-methacrylate (E-GMA) impact modifier was provided by Sumitomo Chemicals Co. Ltd., Japan. Fine talc (Micro ACE series; diameter is 2.5 and 5.0 µm) was purchased from Nippon Talc Co., Ltd. and was used as the filler in RPET.

2.2. Sample Preparation

The sample designations and their corresponding compositions are shown in Table 1. The ratio of RPET: E-GMA was set at 84:16, which was compounded with 0, 10, 15 and 20 wt% of talc in a twin screw extruder (TEX30 HSS, Japan Steel Works Co. Ltd., Japan). The barrel temperature of the extruder was set at 250˚C - 260˚C while the screw rotation speed was 250 rpm. The blend pellets were dried by using a dehumidifying drier at 80˚C for 5 hours prior to being injection molded (UM50, Po Yuen Co. Ltd., China) into dumbbell specimens at a barrel temperature of 280˚C and injection speed of 100 mm/s. The dumbbell specimens will be used for mechanical, morphological and thermal characterizations.

2.3. Characterization

2.3.1. Static Mechaninal Properties

Tensile tests were performed by using an Instron 4206 universal testing machine in accordance to ASTM D638. The gauge length was 115 mm and the test was conducted at an extension rate of 50 mm/min. At least 5 specimens were used to ensure repeatability.

2.3.2. Izod Impact Performance

Notched Izod impact strength was determined for specimens notched at 2 mm depth (a/w = 0.2). The specimens were obtained from the parallel regions of the dumbbell specimens. The tests were conducted by using a Toyo Seiki Izod impact tester with a 5.50 J pendulum at 23˚C in accordance to ASTM D256.

2.3.3. Heat Distortion Temperature

Heat deflection temperature (HDT) of composites was investigated according to ASTMD648 by using the dual

cantilever mode of dynamic mechanical analysis (DMA2980). The standard stress of 0.45 MPa was constantly applied onto the specimens while temperature was increased at 2˚C/min from room temperature. The changes in specimen dimension as a function of temperature was determined. The heat deflection temperature is defined as the temperature at which the specimen deflects 0.25 mm or 0.2% strain.

3. Results and Discussion

3.1. Tensile Properties

Figures 1 and 2 show the tensile properties of the RPET/ E-GMA/talc composites at various talc contents. The tensile modulus of the composites steadily increased with talc content due to the high rigidity of the filler [8], as could be seen in Figure 1. The tensile strength of the composites, however, was drastically reduced when 5 wt% of talc was present in the system, as shown in Figure 2. However with increasing talc content, the tensile strength of the composites was regained, especially when a smaller talc particle size was used.

3.2. Impact Properties

Figure 3 shows the impact strength of the RPET/EGMA/talc composites at various talc contents. With the