Polyethylene, Linear Low Density

Abstract

Linear low density polyethylene (LLDPE) resins are polyethylene (PE) plastic materials with densities in the 0.915–0.925 g/cm 3 range. They are a family of semicrystalline ethylene copolymers with α‐olefins produced in catalytic polymerization reactions. A variety of resins described by the general term LLDPE differ one from another in several respects: the type of α‐olefin used for copolymerization with ethylene (mostly 1‐butene, 1‐hexene, 4‐methyl‐1‐pentene, and 1‐octene), the content of the α‐olefin in the copolymer (it varies from 1 to \documentclass{article}\usepackage{amssymb}\pagestyle{empty}\begin{document}${{\rm{\sim }}10{\hskip0.167em}{\hskip0.167em}{\rm{mol}}{\%}}$\end{document} for different resins), resin density and crystallinity, and compositional uniformity of the copolymers. LLDPE resins are produced in industry with several classes of catalysts: Ziegler catalysts based on titanium or vanadium compounds, Kaminsky and Dow catalysts utilizing metallocene complexes, and Phillips catalysts based on chromium oxides. These resins are manufactured either in gas‐phase, solution, or slurry polymerization processes. LLDPE is a significant commodity product with a worldwide manufacture volume in 1994 of around \documentclass{article}\usepackage{amssymb}\pagestyle{empty}\begin{document}${13\times 10^{6}{\hskip0.167em}{\hskip0.167em}{\rm{tons}}}$\end{document} . Film is the largest application market for LLDPE resins; it is used to manufacture grocery sacks, trash bags, bags for merchandise packaging, garment, laundry, dry‐cleaning, and ice. LLDPE film is also used for nonpackaging applications such as industrial sheeting and agricultural mulch film. High clarity film produced with LLDPE resins manufactured with metallocene catalysts is used for food packaging and medical applications. Injection molding products, mostly for housewares, represent the second largest market for LLDPE. LLDPE resins are also used for blow molding (bottles, drums), for rotational molding (toys, large containers, tanks), for pipe and tubing, and for wire coating in electrical and telephone industry.

Co‐crystallization in ternary polyethylene blends: tie crystal formation and mechanical properties improvement

“…In other words, the linear HD molecules tend to form thick crystalline lamellae with high melting temperature upon cooling, while highly branched LD chains are capable of forming thinner crystals with lower melting temperature. The DSC curve of the LL sample seen in this figure is similar to typical curves of Ziegler − Natta LLDPE resins containing non‐uniform distributed side branches . The main peak of LL lies between the HD and LD peaks at 122.6 °C.…”

Ethylene Polymerization over Metal–Organic Framework Crystallites and the Influence of Linkers on Their Fracturing Process

“…Metal–organic frameworks (MOFs) are another interesting class of porous materials that have been recently used for polymer templating. − MOFs consist of coordination networks with organic ligands connected to metal nodes or cations, containing potential voids upon guest molecule removal . Their well-defined metal sites, together with their porosity, have fostered their use as single-site porous catalysts. − Indeed, a number of MOFs have been studied as solid catalysts for the polymerization and oligomerization of short olefins, due to their industrial relevance and relatively mild conditions required for operation, together with the necessity of fine-tuning selectivity. − Ethylene oligomerization (in both the liquid and the gas phase − ) and polymerization, − as well as propylene dimerization in the gas phase, − or even isoprene polymerization, can be catalyzed by a number of MOFs, postsynthetic modification being necessary in most cases. However, despite its paramount importance in later applications, polymer morphology has been often overlooked and most of the MOF-based catalyst materials described often show either poorly or nonshaped materials.…”