Diffusion and Polymerization Behavior of Styrene in Polyethylene Pellets of Different Molecular Structures†

doi:10.7503/cjcu20170602

Abstract

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

CLC Number:

O631

TrendMD:

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

Figures/Tables 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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