Abstract
This work is aimed to the development of new green composite materials by the incorporation of natural additives into poly(vinyl) alcohol (PVA). Two additives, shredded walnut shells and organic fraction of municipal solid waste (MW), were used to improve the mechanical properties of PVA. Both additives, derived from food industry wastes, were added in a PVA/water solution, which allowed to produce samples by the use of a pressure free process. Rheological analysis was performed in order to study the evolution of the material viscosity during thermal treatment, aimed at water removal. Samples obtained were characterized by means of differential scanning calorimetry (DSC), showing an improvement of the glass transition temperature brought by the addition of walnut shells. Finally, flexural tests were carried out on samples obtained after the incorporation of the different additives in PVA and compared with the mechanical properties of the neat matrix. Results obtained indicate the potential improvement brought by the addition of walnut shells, which allows increasing the flexural modulus of about 50%, at the expenses of a flexural strength reduction of about 30%. Also, at least for low amount of added water, the addition of MW was shown to provide an increase of the strain at break equal to 100%.
Highlights
Poly(vinyl) alcohol (PVA) is a non-toxic, water soluble thermoplastic polymer obtained from the hydrolysis in ethanol of poly(vinyl) acetate
The viscosity evolution during heating was found to be significantly different for the different samples; results reported in Figure 2 show that, at room temperature, the viscosity of PVA_WS is much higher than that of the two other systems, neat PVA and PVA_MW
This is attributed to the water absorption by neat PVA and PVA_MW, in contrast to PVA_WS, which absorbs much lower amounts of water
Summary
Poly(vinyl) alcohol (PVA) is a non-toxic, water soluble thermoplastic polymer obtained from the hydrolysis in ethanol of poly(vinyl) acetate. Unlike other polymers, which were produced starting by their monomer, PVA is obtained by the ester interchange with methanol of acetate groups in presence of anhydrous sodium methylate or aqueous sodium hydroxide (Saxena, 2004). Because of its non-toxic nature, PVA is employed since the first years of twentieth century for food packaging and medical disposals (DeMerlis and Schoneker, 2003). As reported in PVA MSDS, the product is not classified as environmentally hazardous, and is characterized by very low eco toxicity toward different micro-organisms. Because of its high solubility, PVA can be processed at low temperatures, through the addition of water, which brings a liquid solution, at relatively high concentrations of PVA, characterized by very low viscosity (Gaaz et al, 2015).
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