Investigation on chain structure of LLDPE obtained by ethylene in-situ copolymerization with DSC and XRD

Abstract

Thermal segregations of LLDPE were treated with successive self-nucleation/annealing (SSA) on differential scanning calorimetry (DSC). Information on molecular heterogeneity of LLDPE was obtained. After SSA was treated, the multiple endothermic peaks were observed in the DSC thermograms during heating experiment. It is obtained that the thickness of different lamellas formed by segments of various lengths was 4-10 nm. X-ray diffraction (XRD) results showed that the crystallites dimensions of various reflections were about several dozens of nanometers. The ethylene/α-olefin copolymers and the copolymer via in-situ copolymerization were similar to each other for molecular heterogeneity and XRD characteristics, which revealed that it was possible to use the ethylene/α-olefin copolymers to simulate the copolymer via in-situ copolymerization of ethylene to simplify the complexity of the structure of the ethylene in-situ copolymer.LLDPE via in-situ copolymerization, ethylene and α-olefin copolymers, thermal segregation, XRD, DSC Linear low density polyethylenes (LLDPE) are commercially important polymers and are produced via copolymerization of ethylene and α-olefins such as 1-butene, 1-hexene, and 1-octene. Their properties are greatly influenced by various factors. The molecular structure of LLDPE has been investigated from different angles, such as the average content of comonomer, the intramolecular comonomer sequence distribution, and the distribution of comonomer among polymer chains, in addition to average molecular weights and molecular weight distribution. Halasz et al. [1] studied a series of ethylene/1-pentene, ethylene/1-hexene, and ethylene/1-octene copolymers and concluded that the melting temperatures and the crystallinity decrease with increasing chain length of the comonomer and the comonomer content. Moreover, they have investigated the crystallization kinetics of these copolymers. By investigating LLDPE resins based on 1-butene, 1-hexene and 1-octene, Gupta et al. [2] studied the effect of short chain length on the mechanical properties, and found that at higher deformation rates (ca. 1 m/s), the breaking strength of these films increased with increasing short chain branch length. Pan et al. [3] investigated the effect of branched structures on the performances of the copolymers synthesized from ethylene and 1-hexene, 1-decene and 1-tetradecene and 1-octadecene, respectively and found that 16-carbon side branch could co-crystallize effectively with backbone chain at low α-olefin incorporation, which is different from Yoon's result [4] .Recently, much attention has been paid to tandem catalysis of LLDPE production, involving the use of a single feed of ethylene and two catalysts. In this process, one catalyst oligomerizes the ethylene to an α-olefin, and the other is responsible for polymerizing the ethylene and incorporating the α-olefin into the growing polymer chain. Many contributions [5][6][7][8][9][10][11][12][13][14] such as the bi-

Effect of microcarbon particle size and dispersion on the electrical conductivity of LLDPE-carbon composite

“…In Figure 1, which shows the XRD test results for the hybrid polymer-micro carbon-graphite composite, the results are generally similar to the XRD test results for activated carbon processed from rice husk organic material (Swarnalatha et al, 2009). LLDPE as a copolymer with many short branch (Dartora et al, 2015) mostly contain Carbon with crystalline peak at 21,5°, 23,8°, 29,5°, 36,1° (Wang & Yan, 2007) shown in Figures 1.…”

Special morphology and its role in mechanical enhancement of linear low‐density polyethylene/multiwalled carbon nanotubes composites

“…First, the length of crystalline stem, , is determined from the equation: where σ is lamellar basal surface free energy (7 × 10 −6 J/cm 2 ), is equilibrium melting temperature (418 K), is heat of fusion per unit volume (288 J/cm 3 ), and is melting temperature. Then, the inclination of crystalline stems by 35° to the normal of lamellae surface was taken into account in calculation of lamellae thickness : …”

Effect of zeolite 5A on compatibility and properties of linear low‐density polyethylene/thermoplastic starch blend

“…This indicates the complete destruction of A‐type crystalline structure of native starch granules and the formation of V A ‐type crystalline structure by amylose complexed with glycerol or lipids in TPS 28–30. When TPS was melt blended with PE at a TPS to PE weight ratio of 30 : 70, the diffraction peak of TPS at 2θ of 13.5° was hidden by the PE amorphous domain, the peak of TPS at 20.7° overlapped with the peak of the PE crystalline domain, and the original main characteristic peak of PE at 2θ of 21.8° became broader and less intense 31. After incorporating 1–5 wt % of zeolite 5A into the PE/TPS blend, the main characteristic peaks of the PE/TPS blend still existed, and no characteristic peaks of zeolite 5A at 2θ of 7, 10, 24, 31, and 34° were observed, possibly because of the very small amount of zeolite 5A present in the PE/TPS/Z composites.…”