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Preparation and studying of thermoplastic cross-linked polyethylene

 

Cheng Zhi, Mingyuan Hu, Kaige Duan, Chaoxi Zhou, Dongming Yu

Papers # 2018 Las-Vegas

The PE properties are obviously improved by crosslinking modified to TPEX, which can approach to that of PEX, while still remaining thermoplastic. It can be processed by the common forming method of thermoplastic; the products can be hot-melted and the scrap can be processed to be reused. The two-layer structure oxygen-resistant PERT pipe prepared by co-extrusion with EVOH/PERT alloy barrier material does not require adhesive and does not delaminate. The scrap material can be reclaimed by hot melt, the crosslinking modification of PE has made a great breakthrough.

Cross-linked polyethylene pipe has excellent heat resistance and creep resistance, while it can’t be welded by hot melt (fusion) and the scrap can’t be recycled for its property of non-thermoplastic; Polyethylene of raised temperature resistance pipe (PERT) can be melted and the scrap can be processed to be reused, but its temperature resistance and creep resistance is not as high as PEX. In this subject, peroxide and silane methods were used to make low cross-linked modified PERT, which temperature resistance and creep resistance can approach to that of PEX, while still remaining thermoplastic. The performance of thermoplastic crosslinked polyethylene (TPEX) pipe is ideal when the cross-linking degree is about 1% to 3%, which timeout passed the test of 95℃, 1h, 22h, 165h, 1000h hydrostatic pressure, and thermal stability test at 110℃ for 8760h is still under way according to the China PEX pipe standard GB/T18252-2008. The creep test has also achieved satisfactory result by Dynamic thermomechanical analysis (DMA). It is indicated that obtained TPEX is thermoplastic material by testing the melt mass flow rate and the hot-melt welding test of TPEX sheet. The result of 95 degrees centigrade MFR test is 0.057g/10min for 5Kg and 1.441g/10min for 21.6Kg, which still remains thermoplastic; The vicat softening temperature increased about 3℃, which has good heat resistance. At present, TPEX has entered the stage of pilot-scale preparation, which can be made into pipes, bars, monofilaments, films and various injection molding products, even calendering (to be tested) by the common process of PE, its scrap can be hot-melt recycled, its products can be hot-melt welded (fused), it can be widely used in the application field of HDPE (including PERT).

Related keywords : polyethylene; crosslinking; thermoplastic crosslinked polyethylene; TPEX; dynamic crosslinking; tensile creep; constant heat elongation.
Please note that the whole article content is available on PPCA website only


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