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Relationships between thermal history and physical properties of polyolefins

หน่วยงาน จุฬาลงกรณ์มหาวิทยาลัย

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ชื่อเรื่อง : Relationships between thermal history and physical properties of polyolefins
นักวิจัย : Kittisak Chaicharoen
คำค้น : Polyolefins , Recycling (Waste, etc.) , Melting points
หน่วยงาน : จุฬาลงกรณ์มหาวิทยาลัย
ผู้ร่วมงาน : Pranut Potiyaraj , Chulalongkorn University. Faculty of Science
ปีพิมพ์ : 2546
อ้างอิง : 9741745052 , http://cuir.car.chula.ac.th/handle/123456789/3355
ที่มา : -
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Thesis (M.Sc.)--Chulalongkorn University, 2003

This research aimed at studying changes in molecular structure, tensile properties and yellowing of polyolefins upon simulated recycling by reprocessing for 10 cycles. The chosen polyolefins were polypropylene , high density polyethylene and low density polyethylene in both extrusion and injection grades. The plastics, collected at each cycles were tested for their melt flow index, infrared absorbance, tensile strength, elongation, modulus and yellowness index. From the experiments, it was found that properties of all plastics were changed upon processing. The melt flow index of polypropylene was increased as the number of reprocessing cycles increased due to chain scission. The chain scission was resulted from heat and stress occurred during processing. The methyl index, which indicates the change of -CH[subscript3] against -CH[subscript2]-, revealed that methyl groups were increased implying that polymer chains were shortened. Accordingly, tensile strength, elongation and modulus tended to decrease. As for polyethylene, the melt flow index was decreased when the number of cycles increased. It was assumed that the amount of intermolecular cross-linking are advanced to that of chain scission. The results were in agreement with the methyl index which was lower. Tensile strength and modulus were found to be slightly higher while the elongation was diminished. In the case of high density polyethylene, at later cycles, the chain scission was higher so that the melt flow index was increased. Consequently, the tensile strength and modulus were decreased. Generally, these changes are greater in the case of injection process as comparing with extrusion process. This was due to higher stress in the injection process. Yellowing was found in both polypropylene and polyethylene. The increase in yellowness indices of polyethylene was the most significant as comparing to polypropylene. It was assumed that bulky groups in polypropylene chains prohibited the formation of chromophoric groups.

บรรณานุกรม :
Kittisak Chaicharoen . (2546). Relationships between thermal history and physical properties of polyolefins.
    กรุงเทพมหานคร : จุฬาลงกรณ์มหาวิทยาลัย.
Kittisak Chaicharoen . 2546. "Relationships between thermal history and physical properties of polyolefins".
    กรุงเทพมหานคร : จุฬาลงกรณ์มหาวิทยาลัย.
Kittisak Chaicharoen . "Relationships between thermal history and physical properties of polyolefins."
    กรุงเทพมหานคร : จุฬาลงกรณ์มหาวิทยาลัย, 2546. Print.
Kittisak Chaicharoen . Relationships between thermal history and physical properties of polyolefins. กรุงเทพมหานคร : จุฬาลงกรณ์มหาวิทยาลัย; 2546.