Foaming of Ethyl Hydroxyethyl Cellulose

Abstract

The current depletion of petroleum resources together with environmental issues have led to new approaches in plastic manufacturing. This trend involves using ecofriendly materials coming from renewable resources. Good candidates for this, due to their properties and availability, are the cellulose derivatives. Some of them, such as hydroxypropyl methylcellulose (HPMC), showed in previous studies a promising behavior when making polymeric foams. Unfortunately, the corresponding results with methyl ethyl hydroxyethylcellulose (MEHEC) were not as promising and the rather high molecular weight of the used MEHEC grade was here believed to be one of the important factors, affecting the foaming ability. Therefore, in this report, the effect of chain scission and thus the chain length on the foaming behavior of MEHEC was studied. The reduction in molecular weight was achieved through an addition of a degrading agent and salt to aqueous solutions of the original cellulose derivative (MEHEC). After drying, the resulting polymers were characterized, both in the solid state e.g. in the form of films, and as aqueous solutions. This characterization was focused on the rheological behavior. Techniques such as rotational rheometry and dynamic mechanical thermal analysis (DMTA) were used for this purpose. The results pointed to a decrease in molecular weight when adding encreasing amounts of the degrading agent. However, the addition of salt seemed to have an opposite effect, and an increase in viscosity was observed for increasing amounts of salt. A hot-mold process and density measurements were used for assessing the foaming ability. The reduction in molecular weight allowed aqueous solutions with up to 20 and 25 % polymer content to be used in the foaming process (the optimal concentration for the original MEHEC was 5 %). A higher polymer content would be beneficial with regard to large scale processing, like extrusion, one of the most common polymer processing techniques. Additionally, shrinkage was observed in some of the foams and was believed to be associated with the salt content, affecting the foaming ability negatively. Finally, the molecular weight was determined by size-exclusion chromatography (SEC). These SEC-results confirmed the reduction in molecular weight of the MEHEC-grade used.