Thermal degradation of high-density polyethylene ...

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The tensile strength and elongation at break (Eb) decreased inversely .... 14th Day. 1st Day. 21st Day. 3rd Day. Soy spent powder (wt%). Elongation at break (%. ).
J Polym Eng 2015; 35(5): 437–442

Sam Sung Ting*, Norsri Kurniati Achmad, Hanafi Ismail, Ragunathan Santiagoo and Nik Noriman Zulkepli

Thermal degradation of high-density polyethylene/soya spent powder blends Abstract: This study investigates the properties of highdensity polyethylene (HDPE) with different soya spent powder (SSP) blend contents upon oven aging. The aged properties of the HDPE/SSP blends were studied by using tensile test, thermogravimetric analysis, differential scanning calorimetry and Fourier transform infrared analysis. The tensile strength and elongation at break (Eb) decreased inversely proportional to SSP content and aging period. The thermal stability of the blends was significantly reduced after 21 days of aging. After aging, the melting temperature and crystallinity of the blends decreased with increasing aging period. These results revealed that samples with higher SSP content are more brittle upon oven aging. Keywords: high-density polyethylene (HDPE); oven aging; soya spent powder (SSP); tensile properties. DOI 10.1515/polyeng-2014-0095 Received April 30, 2014; accepted October 14, 2014; previously published online December 19, 2014

1 Introduction Polyethylene is an important material for packaging because of its low cost, greater strength and good water *Corresponding author: Sam Sung Ting, School of Bioprocess Engineering, Kompleks Pusat Pengajian Jejawi 3, Universiti Malaysia Perlis, 02600 Arau, Perlis, Malaysia, e-mail: [email protected] Norsri Kurniati Achmad: School of Bioprocess Engineering, Kompleks Pusat Pengajian Jejawi 3, Universiti Malaysia Perlis, 02600 Arau, Perlis, Malaysia Hanafi Ismail: School of Materials and Mineral Resources Engineering, Universiti Sains Malaysia, 14300 Nibong Tebal, Penang, Malaysia Ragunathan Santiagoo: School of Environmental Engineering, Kompleks Pusat Pengajian Jejawi 3, Universiti Malaysia Perlis, 02600 Arau, Perlis, Malaysia Nik Noriman Zulkepli: Center of Excellence Geopolymer and Green Technology (CEGeoGTech), School of Material Engineering, Universiti Malaysia Perlis, Jejawi, 02600 Arau, Perlis, Malaysia

resistance. However, this material is highly resistant to environmental degradation and biodegradation [1]. In order to overcome this problem, many efforts have been done to accelerate the degradation process [2]. Biopolymer is a type of polymer that is made from natural sources such as starch, protein and cellulose. Even though the mechanical properties, rheological properties and processability of biopolymers are comparable with those of synthetic polymers, they are still expensive. Another alternative is to accelerate the degradation process of non-degradable polymers by incorporating natural polymers. Starch is one of the potential materials among the natural polymers that can be used. Starch is generated from carbon dioxide and water by photosynthesis in plants [3]. It can undergo the biodegradation process completely and has lower cost and renewability [4]. Previous studies indicate that starch shows good characteristics when incorporated into synthetic polymers [5, 6]. Research also shows that starch can be used as an additive to prepare biodegradable polyethylene films [7]. There are many kinds of starch that can be applied in synthetic polymers such as wheat starch, rice starch and corn starch [8–10]. Soya spent powder (SSP) is one of the potential natural polymers that can be categorized as a starch. It is an abundant and inexpensive renewable material. It is a by-product of soybean, but it has little commercial value at this time. SSP is suitable for use in commercial processes without further separation. Therefore, its cost is comparable to that of inorganic fillers. Furthermore, SSP has the lowest cost among soya products such as defatted soya flour, soya protein concentrate and soya protein isolate (SPI), whereas SPI has the highest cost [11]. However, the use of soya spent powder in filling polyethylene or other types of polymer is not well established. There is not much reported about the benefits or effects of using soya spent powder in polymer applications. At any rate, degradation of polymers involves biodegradation, hydro-degradation, thermal degradation and physiological degradation. The combination of the degradation effects such as natural weathering and soil burial has been investigated in our previous studies [12–14]. There are many studies on the biodegradation of polymer

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438      S.S. Ting et al.: Thermal degradation of HDPE/SSP blends that have been recently carried out; however, thermal degradation is also one of the important mechanisms to induce the degradation of polyethylene/starch blends. Thermal degradation generally involves changes to the molecular weight and molecular weight distribution of the polymer, and typical property changes include reduced ductility, embrittlement, chalking, color changes and cracking [15]. Indeed, thermal degradation is very useful to enhance the degradation process. Therefore, SSP can be used as a filler into HDPE to make biodegradable polymers owing to its biodegradability and lower market price. In this study, different SSP contents blended with HDPE were investigated. Oven aging was used to perform the thermal degradation process of the blends. The property changes of the blends with aging period were analyzed by using tensile test, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and Fourier transform infrared (FTIR) analysis.

2 Materials and methods 2.1 Material HDPE was supplied by Titan Petchem (M) Sdn Bhd (Pasir Gudang, Johor, Malaysia) in solid pellet form. The melting point was about 180°C, and its melt flow index was approximately 6 g/10 min. Moreover, the specific gravity was 0.940–0.965 g/cm3. The percentage of volatility of the HDPE was