Comparison of Chain Microstructure of Four Polyethylene Resins for Films and Pipes

doi:10.19894/j.issn.1000-0518.240307

Chinese Journal of Applied Chemistry ›› 2025, Vol. 42 ›› Issue (4): 490-498.DOI: 10.19894/j.issn.1000-0518.240307

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Comparison of Chain Microstructure of Four Polyethylene Resins for Films and Pipes

Yu-Xin GAO¹, Wei LIU²(), Rui LI², Yan-Xiong PAN², Deng-Fei WANG¹, Ming-Jun ZHANG¹, Shu-Yan HE¹, Xiang-Ling JI²()

^1.Daqing Petrochemical Research Center，Petrochemical Research Institute of PetroChina，Daqing 163714，China
^2.State Key Laboratory of Polymer Science and Technology，Changchun Institute of Applied Chemistry，Chinese Academy of Sciences，Changchun 130022，China

Received:2024-09-26 Accepted:2024-12-30 Published:2025-04-01 Online:2025-05-14
Contact: Wei LIU,Xiang-Ling JI

Abstract

Abstract:

Polyethylene is one of the most widely used polymer materials in the world. Chain structure parameters including the content and distribution of α-olefin comonomer along the chains in the polyethylene copolymer have significant effects on the properties and applications of polyethylene resin. The chain structure of four ethylene/1-octene copolymers for films and pipes was studied by high-temperature gel permeation chromatography， high temperature ¹³C nuclear magnetic resonance spectroscopy， differential scanning calorimeter and successive self-nucleation and annealing and further compared. The four polyethylene resins are used for casting film （CPE）， polyethylene pipe of raised temperature resistance （PERT）， linear low density polyethylene （LLDPE） packaging and biaxial stretched polyethylene （BOPE） film. The primary chain structure parameters， including relative molecular mass and its distribution， comonomer molar fraction， triad sequence distribution， average ethylene and 1-octene sequence length， average methylene sequence length， were determined and compared. The obtained chain structure information shows that although both CPE and PERT are high density polyethylene， the relative molecular mass of PERT is much higher and the molecular mass distribution is wider， which improve the environmental stress cracking resistance， impact resistance and slow crack growth resistance of PERT pipes by forming more tie molecules between crystalline lamellae. Both LLDPE and BOPE are linear low density polyethylene， but BOPE contains more and longer crystalline sequences， which is conducive to improving the orientation of molecular chains during stretching.

Key words: Polyethylene, Comonomer, Chain structure, Sequence distribution

CLC Number:

O631

Yu-Xin GAO, Wei LIU, Rui LI, Yan-Xiong PAN, Deng-Fei WANG, Ming-Jun ZHANG, Shu-Yan HE, Xiang-Ling JI. Comparison of Chain Microstructure of Four Polyethylene Resins for Films and Pipes[J]. Chinese Journal of Applied Chemistry, 2025, 42(4): 490-498.

Figures/Tables 9

Table 1 Information of the PE resins

Sample	ρ/（g·cm^-3）	MFR/（g·10 min^-1）	Application
CPE	0.961	8.0	Casting polyethylene （CPE） film
PERT	0.941	0.55	Polyethylene of raised temperature resistance （PERT）； Pipes for hot and cold water system
LLDPE	0.920	1.0	Linear low density polyethylene （LLDPE）； Packaging
BOPE	0.912	0.85	Biaxially oriented polyethylene （BOPE）； Packaging

Table 2 Relative molecular mass of the PE resins

Sample	10^-4M_w	10^-4M_n	M_w/M_n
CPE	9.65	2.19	4.42
PERT	19.07	1.98	9.65
LLDPE	14.48	5.56	2.60
BOPE	8.47	2.42	3.50

Fig.1 Molecular mass distribution profiles of CPE （a）， PERT （b）， LLDPE （c） and BOPE （d） resins

Fig.2 FT-IR spectra of CPE （a）， PERT （b）， LLDPE （c） and BOPE （d） resins

Fig.3 13C NMR spectra of CPE （a）， PERT （b）， LLDPE （c） and BOPE （d） resins

Table 3 1-Octene molar fraction， triad sequence distribution， number-average sequence lengths of ethylene and 1-octene in the PE resins

Sample	x（ethylene）/%	x（1-octene）/%	x（EOE）/%	x（OEE）/%	x（EEE）/%	n_E	n_O
CPE	99.8	0.2	0.2	0	99.8	-	1.0
PERT	98.8	1.2	1.2	2.2	96.6	90.5	1.0
LLDPE	97.8	2.2	2.2	4.3	93.5	45.4	1.0
BOPE	97.5	2.5	2.5	2.5	95.0	78.4	1.0

Fig.4 DSC curves of CPE （a）， PERT （b）， LLDPE （c） and BOPE （d） resins upon heating （A） and cooling （B） at a rate of 10 ℃/min

Table 4 Melting temperature， crystallization temperature and crystallinity （Xc） of PE resins measured using DSC

Sample	T_m/℃	T_c/℃	X_c/%
CPE	133.2	118.1	76.5
PERT	125.7	114.6	56.0
LLDPE	110.9/119.6	67.5/107.6	49.0
BOPE	125.3	110.1	41.4

Fig.5 DSC heating scans for CPE （a）， PERT （b）， LLDPE （c） and BOPE （d） resins after SSA thermal fractionation （A） and methylene sequence length （MSL） distribution calculated from SSA thermal fractionation （B）

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Comparison of Chain Microstructure of Four Polyethylene Resins for Films and Pipes

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