Cross-linking studies of PE-VTMS/ Visico : Effects of TiO2 addition on catalyst performance : Kinetics of the cross-linking reaction

Sammanfattning: The aim of the thesis is to study cross-linking catalysts (so-called Ambicats), pigments and cross-linking conditions as cross-linking parameters for PE-VTMS (polyethylene-vinyltrimethoxysilane, Visico). This diploma work consists of two parts; a TiO2-catalyst compatibility study and a cross-linking kinetics study.The TiO2-catalyst compatibility study is an investigation of how titanium dioxide as a white pigment additive is affecting the cross-linking performance of a series of Ambicat catalysts. Commercially available titanium dioxide grades with different coatings and crystal structure have been investigated. The inorganic composition of the coating is detected by electron microscopy. As catalysts in the cross-linking study eight different sulfonic acids have been investigated. All acids have been soaked into polymer pellets to achieve catalyst masterbatches with same concentration of the active group, in order to compare them with the Ambicat (Ufacid K) that is commercially used at Borealis today. The catalyst’s ability to cross-link PE-VTMS alone or in presence of titanium dioxide is measured by the ice method. The goal is to study how Ambicats with different structure and functionality are performing in presence of titanium dioxide of varying crystal structure and coating.The sulfonic acid Ufacid K catalyzes cross-linking of Visico and reaches the highest cross-linking degree. Addition of an inorganically coated titanium dioxide inhibits however the catalyst effect. Uncoated or organic-stabilized anatases are the only titanium dioxide grades that do not passivate Ufacid K. Its isomer Ufacid KW shows similar results. The sulfonic acids that are not that sensitive to the studied titania grades are the naphthalene based CD-2120 and CDX-2190.The purpose with the cross-linking kinetics study is to gain knowledge in methanol’s involvement and effects in the Visico cross-linking process. Studies are performed of how different chemical and physical conditions (water-methanol content, temperature) during the cross-linking reaction affect the final degree of cross-linking. Cross-linking of the samples has proceeded in sealed bottles for certain times and thereafter measurements of the cross-linking degree using decalin extraction were performed.Visico cross-linked in room tempered water reaches after one week a degree of 68%. By raising the temperature a higher cross-linking degree is obtained already after two hours. Pure methanol is the only investigated cross-linking environment which affects the cross-linking negatively. Methanol has the ability to lower the gel content in already cross-linking Visico material.