Abstract
This paper presents a comprehensive study about the application of a lignocellulosic agricultural waste, sunflower husk in different polymer composites. Two types of milled sunflower husk with different geometrical factors were incorporated into polypropylene, low-density and high-density polyethylene, polystyrene (PS), glycol-modified polyethylene terephthalate (PETG) and polylactic acid (PLA). The filler content of the composites varied between 0 and 60 vol%. The components were homogenized in an internal mixer and plates were compression molded for testing. The Lewis–Nielsen model was fitted to the moduli of each composite series, and it was found that the physical contact of the filler particles is a limiting factor of composite modulus. Interfacial interactions were estimated from two independent approaches. Firstly, the extent of reinforcement was determined from the composition dependence of tensile strength. Secondly, the reversible work of adhesion was calculated from the surface energies of the components. As only weak van der Waals interactions develop in the interphase of polyolefins and sunflower husk particles, adhesion is weak in their composites resulting in poor reinforcement. Interfacial adhesion enhanced by specific interactions in the interphase, such as π electron interactions for PS, hydrogen bonds for PLA, and both for PETG based composites.
Highlights
Tensile and flexural strength deteriorated upon the addition of sunflower husk, which were explained by the occurrence of voids during sample preparation as well as by the release of fat residues from the filler during the exothermic cross-linking process resulting in the plasticization of the composite
The results unambiguously proved that coupling improved interfacial adhesion, which changed the dominant micromechanical deformation process from debonding to particle fracture
Six commercially available thermoplastic polymer grades were used as matrix, namely polypropylene (PP), low-density polyethylene (LDPE), high-density polyethylene (HDPE), polystyrene (PS), glycol-modified polyethylene terephthalate (PETG) and polylactic acid (PLA)
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. Tensile and flexural strength deteriorated upon the addition of sunflower husk, which were explained by the occurrence of voids during sample preparation as well as by the release of fat residues from the filler during the exothermic cross-linking process resulting in the plasticization of the composite. There are numerous articles about lignocellulose reinforced composites, in most cases only one or two types of polymers are used as a matrix component This means that quantitative analysis is limited and general conclusions about the role of interactions can hardly be drawn. We selected several thermoplastic polymers having different moduli, different surface energies, and that are capable of forming different intermolecular interactions with the applied filler We filled these polymers with milled sunflower husk in a wide composition range to study quantitatively the effect of interfacial adhesion on the mechanical properties of the composites. We used two types of sunflower husk filler with different size and aspect ratio to investigate the possible role of structure, as well
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