Research progress on regulation of aggregation structure for nascent polyethylene

doi:10.11949/0438-1157.20221089

Abstract

Abstract:

The aggregation structure is one of the key factors to achieve high performance of polyethylene. Starting from the design of aggregation structure of nascent polyethylene, aiming at the problems of excessive entanglement, high viscosity, difficult processing and molding of ultra-high molecular weight polyethylene (UHMWPE), the characterization and regulation of nascent polyethylene chain entanglement and its role in the high performance of polyethylene products are reviewed in this paper. The research progress on the regulation of entanglement of nascent polyethylene is reviewed from the aspects of catalyst structure design and polymerization process design, respectively. It is proposed to increase the growth spacing of active chain on the catalyst surface (spatial scale) and introduce the active chain dormancy technology assisted by nanobubbles in the polymerization process to enhance the chain crystallization rate (time scale) and reduce the“scissors difference”between “chain growth and chain crystallization”. The above two control methods provide theoretical guidance for the efficient preparation of low-entanglement polyethylene on the basis of meeting the harsh industrial production requirements.

Key words: aggregation structure, entanglement, chain crystallization, chain propagation, mechanical property, Ziegler-Natta catalyst, isolator

摘要：

聚集态结构是实现聚乙烯高性能化的关键因素之一，本文从初生态聚乙烯聚集态结构设计出发，针对初生态超高分子量聚乙烯（UHMWPE）普遍存在的缠结过多、黏度过大、加工成型困难等问题，综述了初生态聚乙烯链缠结的表征方法、调控手段及其在聚乙烯产品高性能化中的作用等研究进展。重点从催化剂结构设计和聚合工艺设计两方面介绍了初生态聚乙烯链缠结的调控方法，提出在催化剂表面增大活性链生长间距（空间尺度）和聚合过程中引入“纳微气泡辅助的活性链休眠工艺”强化链结晶速率（时间尺度），缩小“链增长-链结晶”的“剪刀差”。上述两种调控方法为满足工业苛刻的生产要求基础上，实现低缠结聚乙烯的高效制备提供了理论指导。

关键词: 聚集态结构, 缠结, 链结晶, 链增长, 力学性能, Ziegler-Natta催化剂, 阻隔剂

CLC Number:

TQ 320.2

Yuming CHEN, Wei LI, Xiang YAN, Jingdai WANG, Yongrong YANG. Research progress on regulation of aggregation structure for nascent polyethylene[J]. CIESC Journal, 2023, 74(2): 487-499.

陈毓明, 历伟, 严翔, 王靖岱, 阳永荣. 初生态聚乙烯聚集态结构调控研究进展[J]. 化工学报, 2023, 74(2): 487-499.

Figures/Tables 14

Fig.1 Polyethylene consumption of China in 2021[5-8]

Fig.2 Relationship of viscosity and molecular weight of polyethylene

Fig.3 Build-up curves of thermodynamic equilibrium modulus for polyethylene[21]

Fig.4 Protocol of melting-annealing and scheme of chain segment melting-crystallization behavior[23]

Fig.5 CP/MAS measurement results[27]

Fig.6 Schematic diagram of ultra-tensile and thermal conductivity of weakly entangled UHMWPE[40]

Fig.7 Interface healing during sintering and mechanical properties of UHMWPE with different entanglements[44]

Fig.8 Multi-site active sites compositions of CrQCp/FeBIP/CrBIP catalyst[45]

Fig.9 Schematic diagram of the “scissors difference” of “chain growth-chain crystallization”

Fig.10 Schematic diagram of silica surface modified by PMHS[56]

Fig.11 Schematic diagram of MgO/MgCl2/TiCl4 catalyst structure[60]

Fig.12 Schematic diagram of separated active sites and molecular chains by POSS isolators [60,63,69]

Fig.13 Nitrogen nano/micro-bubble assisted process diagram

Fig.14 Schematic diagram of spatial scale and temporal scale reduction of “scissors”

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