苯乙烯单体对不同分子形态聚乙烯的扩散聚合行为

doi:10.7503/cjcu20170602

摘要/Abstract

摘要：

采用苯乙烯(St)单体对具有不同分子形态的聚乙烯(PE)进行了扩散聚合行为研究. 结果表明, 与高密度聚乙烯(HDPE)和线性低密度聚乙烯(LLDPE)相比, 由于低密度聚乙烯(LDPE)中长支链的存在导致其结晶度最低, 因此LDPE能够为St单体扩散提供更多的自由体积, 故St单体的扩散速率最快, 聚苯乙烯(PS)扩散饱和值最高. PS在不同种类的PE颗粒中均呈现为“M”型分布, 且在不同PE颗粒中PS纳米微球粒径基本相同. 部分扩散到PE颗粒内部的St会对PE接枝形成PE-g-PS, 这种接枝物在相界面处可作为相容剂减小分散相的尺寸, 增加分散相和基体间的界面黏合力, 同时可使材料的拉伸强度和杨氏模量得到明显提高.

关键词: 聚乙烯, 苯乙烯, 结晶度, 扩散, 聚合

Abstract:

Diffusion and polymerization behavior of styrene(St) in polyethylene(PE) of different molecular structures were studied. The results show that low density polyethylene(LDPE) could provide more free volume for the diffusion of styrene than high density polyethylene(HDPE) and linear low density polyethylene(LLDPE) because of its lowest crystallinity. Therefore, the diffusion rate of styrene in LDPE pellets is the fastest, and the maximum amount of styrene diffusion is also the highest. Polystyrene(PS) has a distinct distribution of “M” type in different PE pellets and the size of PS nanoparticles is almost indentical. PE-g-PS at the interface, generated by chemical grafting of styrene onto PE molecules, can act as compatibilizer, reducing the size of the dispersed phase and increasing the interfacial adhesion between the dispersed phase and the matrix, and therefore the tensile strength and Young’s modulus are significantly improved.

Key words: Polyethylene, Styrene, Crystallinity, Diffusion, Polymerization

中图分类号:

O631

TrendMD:

黄承焕, 陈韵乐, 郭朝霞, 于建. 苯乙烯单体对不同分子形态聚乙烯的扩散聚合行为. 高等学校化学学报, 2018, 39(3): 558.

HUANG Chenghuan, TAN Yinle, GUO Zhaoxia, YU Jian. Diffusion and Polymerization Behavior of Styrene in Polyethylene Pellets of Different Molecular Structures^†. Chem. J. Chinese Universities, 2018, 39(3): 558.

图/表 11

Scheme 1 Schematic diagram of molecular chain structure of HDPE, LDPE and LLDPE

Table 1 Measurement of the crystallinity of different PEs

PE	T_m/℃	ΔH_m/(J·g^-1)	X_c(%)	T_c/℃	ΔH_c/(J·g^-1)
HDPE	129.3	169.4	62.7	115.0	156.2
LDPE	107.7	88.1	32.6	92.8	80.6
LLDPE	126.9	145.5	53.9	112.7	140.3

Fig.1 PS content as a function of diffusion time for HDPE(4902T)(a), LDPE(LD607)(b) and LLDPE(D2027)(c)

Fig.2 FESEM images of the cross-section of HDPE and HDPE/PS nanoalloy pellets(A) HDPE; (B) surface of HDPE/PS; (C) mid-depth from the surface to the center of HDPE/PS; (D) center of HDPE/PS.

Fig.3 FESEM images of the cross-section of LDPE(A) and LDPE/PS(B—D) nanoalloy pellets(A) LDPE; (B) surface of LDPE/PS; (C) mid-depth from the surface to the center of LDPE/PS; (D) center of LDPE/PS.

Fig.4 FESEM images of the cross-section of LLDPE and LLDPE/PS nanoalloy pellets(A) LLDPE; (B) surface of LLDPE/PS; (C) mid-depth from the surface to the center of LLDPE/PS; (D) center of LLDPE/PS.

Fig.5 Micro-FTIR profiles of PE/PS pellets along the diameter directiona. HDPE(4902T)/PS; b. LDPE(LD607)/PS; c. LLDPE(D2027)/PS.

Fig.6 FTIR spectra of PE/PS pellets a. PE; b. HDPE/PS; c. LLDPE/PS;d. LDPE/PS.

Table 2 Graft ratio and peak area ratio of PE/PS nanoblends

PE/PS	PS content(%)	Graft ratio(%)	Peak area ratio of PS/PE
HDPE/PS	16.0	1.20	0.03
LDPE/PS	19.3	5.63	0.14
LLDPE/PS	18.1	4.85	0.12

Fig.7 FESEM images of the cross-section of PE/PS injection-molded(A) HDPE/PS; (B) LDPE/PS; (C) LLDPE/PS.

Table 3 Mechanical properties of PE and PE/PS injection-molded bar

System	Young’s modulus/MPa	Tensile strength/MPa	Elongation at break(%)
HDPE	1006.3±65.3	21.3±0.5	29.0±4.0
HDPE/PS	1134.1±38.4	24.6±0.3	54.1±0.3
LDPE	140.9±2.6	10.2±0.2	113.1±3.9
LDPE/PS	205.6±3.8	11.5±0.1	106.7±2.5
LLDPE	334.9±6.4	16.3±0.4	450.1±7.7
LLDPE/PS	434.7±14.1	18.5±0.3	454.5±0.1

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