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Novel Ethylene-α-olefin Copolymer Elastomers and Their Toughening Modification for Co-polyprolene

Author: LiChen
Tutor: LiBoGeng；FanHong
School: Zhejiang University
Course: Chemical processes
Keywords: Ethylene-α-olefin copolymer OBC Co-PP toughening
CLC: TQ325.14
Type: Master's thesis
Year: 2010
Downloads: 363
Quote: 5
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Abstract

Olefin Block copolymer (OBC) is a novel ethylene-octane copolymer with alternating blocks of "hard" and "soft" segments. It’s produced through Chain-Shuttling Polymerization using two non-metallocene catalysts in the presence of a non-catalytic "chain-shuttling agent" agent to transfer growing chains between two distinct catalysts. Due to its unique block structure, OBC delivers novel combinations of end-use properties and processability at a "cost-in-use" competitive with other random olefin copolymers, and is becoming as a new impact modifier for general plastics modifications.In this paper, the structure and basic propertities of Olefin Block copolymer (OBC) and several other ethylene-α-olefin copolymers were characterized with the aids of NMR, DSC, rheometer and DMA analysis. The relations between the structural parameters of above polymers and their melt crystallization, viscoelastic and dynamic mechanical properties were discused. It was found that melting temperature, crystallization temperature and crystallinity reduced with increasing comonomer content and the length of the short branched chain of the random copolymers. Compared with the random copolymer POE and non-uniform ethylene-propylene copolymer, OBC, containing high comonomer content, still exhibits a higher melting temperature and crystallinity, due to its unique hard and soft block structure. Moreover OBC shows better heat resistance property and faster injected and extrusion.Dynamic rheology ananlysis results indicated that OBC exhibited the low complex viscosity under the low frequency which relating to the structure of OBC. Moreover, the absence of long branching chain in OBC, decreased its zero shear viscosity and characteristic relaxation time in the melt states. OBC has higher melt index, lower complex viscosity and higher viscous flow activation energy, indicating its high viscosity temperature sensitive and a good processing flowability.Dynamic mechanic ananlysis was used to investigate the relationships between elastic preoperties and structure parameters of seven different olefin copolymers. Analysis results showed that increasing the comonomer content, the length of short side chain and introduing the long braching chain in olefin copolymer molecules will decreses the storage modulus of the copolymer at low temperatue and shift theβtransition temperature to lower temperature, which would endow the copolymer with better impact properties at low temperature. While the longer short branched chain of copolymers has the better elastic properties. So among the present commercial polyolefin elastomers, ethylene-octene copolymer has more superior for its flexibility and elasiticity. Unlike to the random type POE, the new block copolymer OBC although having a higher comonomer contentm, maintains a higher crystallinity, and the corresponding hard segments in OBC could play the role of physical cross-linking points and soft segment enhance the mutual entanglement. So OBC has lower storage modulus and stronger (3 transition which cooresponding to its better toughness performances.Based on the above study, the mechanical, physical properties and toughening mechanism of Co-PP/OBC blends were investigated and compared with the other PP/ polyolefin elastomers blends. Experimental results show that the critical elastomer content at brittle-ductile transition for the Co-PP/elastomer blends is lower than PP/ elastomer blends because the Co-PP contains a certain mount of ethylene-propylene copolymer which cooperates with the added elastomers. For the metallocene catalyzed olefin copolymer elastomers studied, it was found that the brittle-ductile transition content of Co-PP/POE blends is lower than Co-PP/mEPDM and Co-PP/mEBC blends, and POE was considered as a better toughening agent because the Co-PP/POE blend exhibited higher impact strength at room and low temperature. Also Co-PP/POE blend showed higher tensile strength, heat resistant and good processing properties.Compared with the Ziegler-Natta catalyzed EPDM, OBC and POE exhibited better toughening efficiency for Co-PP concering to the properties of impact strength, tensile strength and elongation at break. Especially, the Co-PP/OBC blend showed the best impact resistence performance at low temperature.The impact strength of Co-PP/OBC blend under -20℃is equal to the Co-PP/EPDM blend at room temperature and is better than Co-PP/POE blend, which indicating the better toughness effects of OBC at low temperature. The results were also confirmed by the DMA analysis of Co-PP/olefin elastomer blends. The melt flow index and the Vicat softening point of Co-PP/OBC blends are both significantly higher than Co-PP/POE at the same content of elastomer, which indicating that the unique block structure of OBC is propitious to maintain good processing and heat resistance properties. So, as a novel polyolefin elastomer, OBC could be used as an excellent toughening agent for Co-PP modification.

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CLC: > Industrial Technology > Chemical Industry > Synthetic resins and plastics industry > Polymer resin and plastic > Polyolefin plastic > Polypropylene
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