Abstract
A poly(urethane-acrylate) polymer (PUA) was synthesized, and a sufficiently high molecular weight starting from urethane-acrylate oligomer (UAO) was obtained. PUA was then loaded with two types of powdered ligno-cellulosic waste, namely from licorice root and palm leaf, in amounts of 1, 5 and 10%, and the obtained composites were chemically and mechanically characterized. FTIR analysis of final PUA synthesized used for the composite production confirmed the new bonds formed during the polymerization process. The degradation temperatures of the two types of waste used were in line with what observed in most common natural fibers with an onset at 270 °C for licorice waste, and at 290 °C for palm leaf one. The former was more abundant in cellulose (44% vs. 12% lignin), whilst the latter was richer in lignin (30% vs. 26% cellulose). In the composites, only a limited reduction of degradation temperature was observed for palm leaf waste addition and some dispersion issues are observed for licorice root, leading to fluctuating results. Tensile performance of the composites indicates some reduction with respect to the pure polymer in terms of tensile strength, though stabilizing between data with 5 and 10% filler. In contrast, Shore A hardness of both composites slightly increases with higher filler content, while in stiffness-driven applications licorice-based composites showed potential due to an increase up to 50% compared to neat PUA. In general terms, the fracture surfaces tend to become rougher with filler introduction, which indicates the need for optimizing interfacial adhesion.
Highlights
A considerable amount of ligno-cellulosic waste is produced in several industries, spanning from the food sector to the manufacturing of furniture or to the disposal of vegetable refuse, after pruning or cutting operations
The numbers in bold indicate the different chemicals used for synthesis and obtained after that
Licorice root waste provided an increase in composite hardness compared to PUA-palm leaf and PUA-licorice root composites
Summary
A considerable amount of ligno-cellulosic waste is produced in several industries, spanning from the food sector to the manufacturing of furniture or to the disposal of vegetable refuse, after pruning or cutting operations. A possibility to re-use with an upcycling concept, giving economical value to this process, can be its introduction as a filler in polymers. This process does normally require compatibilization to improve the wettability and adhesion of ligno-cellulose waste to the matrix [1]. Another significant factor to be accounted for is the geometry of the filler to be introduced. The improved physico-chemical performance of cellulose fibers when modified with poly(urethane-acrylate) (PUA) copolymers is well known [4]. During the last few decades, PUA has been widely used as tissue adhesives as well as UV coatings due to its unique properties as excellent abrasion resistance, adhesion to substrates, light stability, and weatherability [5]
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