Optimization of the synthesis of uhmwpe for preparing high-strength fibers from spinning solution

Abstract

Data on the possibility of preparing in high yield reactor powders of ultra-high-molecular-weight polyethylene deposited on titanium-magnesium catalysts were presented. The powders had controlled morphology, supramolecular structure, and molecular weight and were suitable for producing highstrength fibers by gel formation.Ultra-high-molecular-weight polyethylene (UHMWPE) of molecular weight (MW) (1-5)·10 6 g/mol is used as starting raw material in gel technology for producing high-strength fibers. Reactor powders (RP) of UHMWPE that are synthesized using Ziegler-type catalysts (CT) usually act as such raw material. The required MW for the UHMWPE can be obtained by adjusting the synthesis conditions. However, the MW is not the only parameter that determines the fiberforming properties of a spinning solution. These properties depend considerably on the solution homogeneity, the degree of crystallinity, and structural features of the RP macromolecule. These determine the uniformity and strength of the molecular network that will be transformed into a highly ordered structure during orientational drawing. Thus, despite the fact that the supramolecular structure of the RP is completely lost upon dissolution [1], the properties of the final product (in this instance fiber) depend on the morphology and molecular characteristics of the RP (grain size, grain connectivity, molecular structure of the ordered phase, etc.) that are formed under the influence of the CT [2-6].The principal trends in the relationship of the parameters of the primary synthesized polymer and the synthesis conditions are well known {e.g., as the polymerization temperature decreases, the polyethylene (PE) MW increases, the bulk RP density decreases, etc.[7]}. However, it is extremely difficult to predict that properties of the final product, in this instance highly oriented fiber, at the synthesis stage without establishing even just the general trends in the change of fiber properties as a function of the CT and the polymerization process parameters.Herein data on the effect of several UHMWPE RP synthesis parameters on the mechanical properties of highly oriented fibers produced under identical conditions from gel precursors and obtained by spinning from solutions are presented in order to identify such trends. The RP were synthesized on titanium-magnesium CT using a polymerization suspension of ethylene in a hydrocarbon diluent at 45-65°C. The active component of the CT was TiCl 4 deposited on highly disperse (activated) MgCl 2 modified by additional components that enabled the RP morphology and polymer MW to be controlled.Three groups of RP samples designated arbitrarily A, B, and C (Table 1) were investigated using three CT modifications TMK-A, TMK-B, and TMK-C, respectively. The temperature and time of the polymerization were varied within each group in order to produce PE with the required MW and in sufficiently high yield.

Direct synthesis of fibrous high molecular weight polyethylene using vanadium catalysts supported on an SiO2ionic liquid system

“…Interestingly, vanadium catalysts immobilized on a solid carrier, e.g. magnesium chloride or silica, produce polyethylene characterized by a high molecular weight, despite a broad molecular weight distribution . Polyethylene, especially high molecular weight polyethylene, is an attractive product because of its good physical and mechanical properties.…”