Oligomere Polyvinylester zur Entwicklung duktiler Polyvinylacetat-Barrierematerialien

• Oligomeric poly(vinyl esters) for the preparation of ductile poly(vinyl acetate) barrier materials

Heinze, Daniel; Möller, Martin (Thesis advisor); Mang, Thomas (Thesis advisor)

Aachen : Publikationsserver der RWTH Aachen University (2015)
Dissertation / PhD Thesis

Aachen, Techn. Hochsch., Diss., 2015

Abstract

The present PhD thesis deals with the development of oligomeric poly(vinyl esters) as additives for the preparation of ductile poly(vinyl acetate) (PVAc) barrier materials with low oxygen permeability by melt compounding. In order to synthesize the poly(vinyl esters) exhibiting an aliphatic side chain length of 2-18 carbon atoms and degrees of polymerization of 10 and 20, the telomerization of vinyl esters using carbon tetrachloride as chain transfer agent proved to be a convenient method. The thermal properties of these chlorinated oligomers were significantly affected by the side chain length. It was highly important that the use of a longer side chain increased drastically the resistance to degradation resulting in stable oligomers from a length of 8 carbon atoms. In contrast, a reduction became necessary to stabilize the chlorinated poly(vinyl acetate). Oligomeric poly(vinyl acetate) with a degree of polymerization of 10 presented an efficient plasticizer for brittle, commercial PVAc during melt mixing in a microcompounder and acted as compatibilizer to improve the dispersion of an organically modified layered silicate in the PVAc matrix. The latter was based on its low molecular weight leading to a lower radius of gyration compared to the interlayer spacing of the filler. At this, the masterbatch method presented the most successful approach for the compounding with the layered silicate. Using this method, plasticized nanocomposites with a significantly higher oxygen barrier than the pure poly(vinyl acetate) were obtained up to a filler content of 7.5 wt %. Therefore, the study demonstrates that ductile PVAc materials with low oxygen permeability can be prepared via two-step melt compounding (masterbatch method) using oligomeric poly(vinyl acetate) as additive and layered silicate as nanofiller. In case of poly(vinyl acetate), this approach opens up new fields of application since it eliminates the brittleness of PVAc and, unlike the conventional use of PVAc in dispersions, is solvent-free and compatible with current industrial processes. For example, the plasticized PVAc films provide a promising alternative for barrier materials due to the good thermoplastic processability of PVAc and lower oxygen permeability in comparison to polyolefins. However, it has to be taken into account that an exfoliation was not achieved. The PVAc-layered silicate nanocomposites could not substitute the common barrier polymers in terms of oxygen barrier properties due to higher O2 permeability. In addition, a scale-up, a more precise migration analysis of the oligomer and a review of the regulations for nanoparticles will be inevitable for a commercialization of the PVAc materials. Nevertheless, due to the advantages of extrusion processing, the masterbatch method used in this work presents an interesting way to enhance the compatibility of a polymer matrix with layered silicates and simultaneously ensure its effective plasticization by the addition of an oligomer with chemical constitution being identical to the matrix. This could provide an attractive approach for other commercially important polymers and should be extensively investigated in the future.