Abstract
This study compares the degradation process of unsaturated polyester resin (UPR) and vinyl ester resin (VER) and their biocomposites with kraft lignin. In order to study their degradation, accelerated aging, immersion in different solvents, microwave radiation and high temperature were applied. The results show that, depending on the conditions, the degradation assumes a different course. The VER resin is more chemically resistant than the UPR resin. In the case of the composites immersed in an aggressive solvent (acetone), it can be observed that the polymer matrix is degraded, whereas in water only a small increase of weight takes place. Immersion in NaOH initiates the degradation process consisting in the hydrolysis of ester bonds, which are especially observed for pure resins. Under the influence of UV radiation and microwaves, the resins are additionally cross-linked. Thermogravimetric analysis shows that in the case of composites heated to 1000 °C, a residual mass remains, which is carbonized with lignin. In turn, composites treated with microwaves lost weight.
Highlights
Lignin is a natural biopolymer containing aromatic moieties in its chemical structure
This paper presents the results of research on the degradation of unsaturated polyester resin and vinyl ester resin composites containing the common biofiller—lignin
Compared to the unsaturated polyester resin (UPR), the vinyl ester resin (VER) proved to be more resistant to water degradation
Summary
Lignin is a natural biopolymer containing aromatic moieties in its chemical structure. It is mainly applied in the paper industry, but it can be a unique precursor for the production of activated carbons, adhesives, biofuels, carbon fibers, and as a source of fine chemicals and phenolic monomers. Most of the lignin from the pulp and paper industry is used for energy production and is burned in a chemical recovery stage. There are three phenolic monomers in the chemical structure of lignin: coumaryl, coniferyl and syringyl. These molecules are collectively called monolignols [1]. Kraft lignin is a type of industrial lignin whose world production exceeds 85% of the total lignin production [2]
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