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Lignin-based polyurethane and epoxy adhesives: a short review

dos Santos D.J., Tavares L.B., Gouveia J.R., Batalha G.F.

Archives of Materials Science and Engineering

2021

Vol. 107, nr 2

56--63

Purpose: of this paper was to review and summarize significant papers related to the development and characterization of lignin-containing adhesives: polyurethane and epoxy types. In the last decades, several efforts have been dedicated on the development of renewable raw materials for polymer synthesis, mainly due to petroleum depletion and sustainability. In this context, lignin emerged as a potential candidate to substitute fossil-based raw materials in adhesive synthesis and formulations. Design/methodology/approach: Recent and other relevant papers were reviewed, aiming to identify the main advantages and limitations involved in lignin incorporation into epoxy and polyurethane adhesives formulations. First, effects of unmodified lignin addition were presented. Afterwards, the main lignin chemical modification methods were presented and discussed, based on thermomechanical results. Findings: Incorporation of unmodified lignin usually is limited to 30 %wt., otherwise mechanical properties are drastically affected as consequence of poor lignin solubility and excessive brittleness. Lignin chemical modification can be used to increase the reactivity of hydroxyl groups and/or add new moieties in its molecular structure, improving solubility and thermomechanical properties of cured adhesives. Practical implications: In the last years, some industrial plants started to operate and produce technical grade lignin at industrial scale, with reproducible properties and controlled molecular structure. Therefore, increasing efforts have been dedicated from researchers and chemists to develop lignin-based technologies, in which this work can directly contribute with. Originality/value: As consequence of the high content of phenol groups in its molecular structure, lignin was mostly applied on the development of phenolic resins applied as wood adhesives. For the first time in the literature, this work summarizes the advances related to synthesis and characterization of polyurethane and epoxy, applied as adhesives. Results can support the development and application of biobased, as well as contribute to the revalorization of this valuable and readily available biomass.

Bio-based polyurethane applied as matrix of fiberglass reinforced composite

de Sousa Jr. R. R., Miranda E. A., Batalha G. F., dos Santos D. J.

Journal of Achievements in Materials and Manufacturing Engineering

2017

Vol. 81, nr 1

5--10

Purpose: of this paper was to develop and to characterize the mechanical behaviour of a structural composite obtained from a bio-based polyurethane matrix reinforced with fiberglass. Design/methodology/approach: Castor oil and Kraft lignin-containing polyol was applied for bio-based polyurethane synthesis. Structural composite was obtained by reinforcing this renewable source bio-based polymer with fiberglass mat. Polyester resin composite was also obtained for comparison, following the same process and reinforcement conditions. Mechanical characterization was carried out through uniaxial tensile, flexural strength, Izod impact tests and additionally scanning electron microscopy (MEV). Findings: Bio-based polyurethane composite was obtained and presented higher ultimate tensile strength (UTS) and equivalent impact resistance in comparison to polyester matrix composite. Research limitations/implications: Effects of Kraft lignin and fiberglass contents changing on mechanical properties might be investigated in future researches. Practical implications: Revalorization of Kraft lignin. 50 million tons of lignin are produced worldwide every year as by-product of pulp and paper manufacturing. The most part of this Kraft lignin is currently burned for energy generation. Originality/value: Results indicated the possibility of reusing this industrial wasted by-product at large scale as polymeric matrix for structural composite, in which high UTS and impact resistance are required.