Abstract
Nowadays, the chemical industry is looking for sustainable chemicals to synthesize nanocomposite bio-based polyurethane foams, PUs, with the aim to replace the conventional petrochemical precursors. Some possibilities to increase the environmental sustainability in the synthesis of nanocomposite PUs include the use of chemicals and additives derived from renewable sources (such as vegetable oils or biomass wastes), which comprise increasingly wider base raw materials. Generally, sustainable PUs exhibit chemico-physical, mechanical and functional properties, which are not comparable with those of PUs produced from petrochemical precursors. In order to enhance the performances, as well as the bio-based aspect, the addition in the polyurethane formulation of renewable or natural fillers can be considered. Among these, walnut shells and cellulose are very popular wood-based waste, and due to their chemical composition, carbohydrate, protein and/or fatty acid, can be used as reactive fillers in the synthesis of Pus. Diatomite, as a natural inorganic nanoporous filler, can also be evaluated to improve mechanical and thermal insulation properties of rigid PUs. In this respect, sustainable nanocomposite rigid PU foams are synthesized by using a cardanol-based Mannich polyol, MDI (Methylene diphenyl isocyanate) as an isocyanate source, catalysts and surfactant to regulate the polymerization and blowing reactions, H2O as a sustainable blowing agent and a suitable amount (5 wt%) of ultramilled walnut shell, cellulose and diatomite as filler. The effect of these fillers on the chemico-physical, morphological, mechanical and functional performances on PU foams has been analyzed.
Highlights
Since the publication of the principles of “green chemistry” at the end of 1990s by Anastas and Werner [1], a great effort related to improving the treatment, synthesis and disposal of chemical substances was made by scientific community
CH3 COOK and Niax PM40 additives were used to control both polymerization and blowing reactions, and L6164 was used as surfactant to stabilize the cells in the PU foam; both were kindly provided by Momentive (Terni, Italy)
Foam density was calculated as the ratio between the weight and geometric volume of composite
Summary
Since the publication of the principles of “green chemistry” at the end of 1990s by Anastas and Werner [1], a great effort related to improving the treatment, synthesis and disposal of chemical substances was made by scientific community. Attention has principally gone to those issues aimed to protect the environment and preserve its resources for future generations. For these reasons, given that the crude oil is a limited resource, research has to develop other processes to produce materials starting. Materials 2020, 13, 211 from eco-friendly and sustainable source [2,3,4,5]. In this contest, biomass, waste and by-product from different industrial sectors have gained interest as sustainable source to obtain chemicals that can be used (or re-used) in several industries [6]. The same drawbacks have motivated continued research focus in developing green routes by using sustainable or renewable sources to develop bio-based Polyurethanes [8,9]
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