Formation of all-biopolymer-based composites with cellulose as the main component†

The continuously growing concerns connected to the pollution produced by the extensive use of non-biodegradable composites strongly justify the need to find renewable and bio-degradable alternatives which are able to replace the already established synthetic composite materials. All-biopolymer composites with cellulose as the main component are emerging as excellent replacement candidates, combining full biodegradability with interesting properties. In the present work, such composites containing a cellulose-based textile reinforcement and a biopolymer-based matrix were prepared by two routes: 1) partial dissolution of the reinforcement fibers by impregnation with an ionic liquid (IL) to generate the matrix, or 2) impregnation of the reinforcement with a biopolymer-containing solution in an IL : DMSO mixture as a precursor for the matrix. For both routes, subsequent immersion in water to induce phase separation and thermal drying to complete the lamination yielded the final materials. The influences of the reinforcement textile composition (cotton vs. linen) and matrix generation route as well as the structure of the IL (route 1) or additional biopolymer (cellulose vs. chitosan; route 2) on the composite structure formation and the resulting mechanical properties were investigated in detail. Very high tensile modulus values of ∼2.8 ± 0.4 GPa and ∼3.3 ± 0.4 GPa were recorded for the composites obtained by the impregnation of a cotton textile with pure ionic liquids 1-ethyl-3-methyimidazolium acetate (EmimOAc) and 1-butyl-3-methylimidazolium acetate (BmimOAc), respectively. The tensile moduli of the composites obtained by the impregnation with BmimOAc were higher than the ones of the composites obtained under the same conditions by the impregnation with EmimOAc. Additionally, the composites obtained by the impregnation of the reinforcement textiles with a diluted solution of a similar biopolymer, namely chitosan, were less hydrophilic, as demonstrated by the increase of the contact angle from below 40° to ∼80°.