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Light weight and sustainability are the key drivers in the development of novel biobased thermoplastic compounds for automotive applications. This paper reports the engineering properties of thermoplastic compound consisting of a novel bioresourced carbon filler in combination with partially biobased poly­(trimethylene terephthalate). The bioresourced carbon filler, which was derived from lignin residue of cellulosic ethanol production, has a clear advantage in terms of density compared to glass fiber and other minerals, and shows potential for weight reduction with 7% lower density at 20% filler content. Polymer processing conditions were optimized in terms of thermomechanical properties, and use of a reactive chain extender additive was studied for improving the performance of the compound. At the optimized conditions, good dimensional stability, 89% increase in heat deflection temperature, 60% increase in flexural modulus, and 14% increase in flexural strength was attained in comparison to neat PTT polymer. Theoretical modeling based on a rule-of-mixture approach showed good agreement of the predicted and experimental modulus of the studied composites. When compared to existing mineral filled engineering polyester resin, many properties of the prepared compounds were on a comparable or favorable level, indicating good potential of the bioresourced carbon filler for light weighting and highly sustainable engineering applications.

Viscoelastic properties of cellulose microfibril-polymer composites and paper sheets were studied with dynamic mechanical analysis as a function of relative humidity in order to assess the bonding properties in cellulosic networks. The amount of associated water in the composites (equilibrium moisture content) was measured by thermogravimetry. Water plasticization was evidenced by DMA both in composite and paper samples. Polymers with high affinity to water, e.g. carboxymethyl cellulose, clearly increased the water plasticization in the composites. The plasticization behavior of paper sheet samples was also influenced by polymers. However, the effect of polymers on the plasticization was different between the composite and the paper samples. The consideration of fiber bonding domain in paper structure as a gel-like layer consisting of cellulose microfibrils, polymers, and associated water can help to unveil some of the complex mechanisms behind the strength in fibrous cellulosic materials.

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