Optimizing the Process Efficiency of Reactive Extrusion in the Synthesis of Vinyltrimethoxysilane-Grafted Ethylene-Octene-Copolymer (EOC-g-VTMS) by Response Surface Methodology.

Andreas Kandelbauer,Thomas Chassé,Steffen Ulitzsch,Günter Lorenz,Tim Bäuerle

doi:10.3390/polym12122798

Andreas Kandelbauer, Thomas Chassé + Show 3 more

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https://doi.org/10.3390/polym12122798

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Journal: Polymers	Publication Date: Nov 26, 2020
Citations: 10	License type: CC BY 4.0

Affiliation: Reutlingen University, University of Tübingen

Abstract

Thermoplastic polymers like ethylene-octene copolymer (EOC) may be grafted with silanes via reactive extrusion to enable subsequent crosslinking for advanced biomaterials manufacture. However, this reactive extrusion process is difficult to control and it is still challenging to reproducibly arrive at well-defined products. Moreover, high grafting degrees require a considerable excess of grafting reagent. A large proportion of the silane passes through the process without reacting and needs to be removed at great expense by subsequent purification. This results in unnecessarily high consumption of chemicals and a rather resource-inefficient process. It is thus desired to be able to define desired grafting degrees with optimum grafting efficiency by means of suitable process control. In this study, the continuous grafting of vinyltrimethoxysilane (VTMS) on ethylene-octene copolymer (EOC) via reactive extrusion was investigated. Successful grafting was verified and quantified by 1H-NMR spectroscopy. The effects of five process parameters and their synergistic interactions on grafting degree and grafting efficiency were determined using a face-centered experimental design (FCD). Response surface methodology (RSM) was applied to derive a causal process model and define process windows yielding arbitrary grafting degrees between <2 and >5% at a minimum waste of grafting agent. It was found that the reactive extrusion process was strongly influenced by several second-order interaction effects making this process difficult to control. Grafting efficiencies between 75 and 80% can be realized as long as grafting degrees <2% are admitted.

Highlights

Ethylene-octene copolymer (EOC) is a promising material for biomaterial applications because of its favorable mechanical and interfacial properties [1,2]
It was found that the reactive extrusion process was strongly influenced by several second-order interaction effects making this process difficult to control
For example, at a low-temperature increase and low ethylene-octene copolymer (EOC) feed rate, the di(tert-butylperoxy) hexane (DTBPH) feed rate is doubled from 1 g/h to 2 g/h at a VTMS feed rate of 40 g/h, the grafting efficiency of the process is increased from approx. 55–60% to significantly more than 70% (Figure 8c)

Summary

Introduction

Ethylene-octene copolymer (EOC) is a promising material for biomaterial applications because of its favorable mechanical and interfacial properties [1,2] Like other polyolefins, it allows adhesion of living cells on its surface and improves surface adsorption phenomena in general when present in a composite [3,4]. Even with higher loads of peroxide, the possible crosslinking degrees are often not satisfactory [7] Another possibility to cross-link EOC is via condensation after previous modification with a suitable silane [8]. Silane grafting with vinyltrimethoxysilane (VTMS) is the most commonly applied method in this context [9,10,11,12] By this approach, it is possible to crosslink the VTMS modified polyolefin via a condensation reaction with silicones and, in turn, thereby increase the adhesive strength and compatibility of the silicone. The application range of both, the EOC as well as of the silicone is thereby significantly enhanced

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