Tailoring the Properties of Biocomposites by Silane Coupling Agents and Graphene Nanoplatelets
Rajan, Rathish (2022)
Tampere University
2022
Teknisten tieteiden tohtoriohjelma - Doctoral Programme in Engineering Sciences
Tekniikan ja luonnontieteiden tiedekunta - Faculty of Engineering and Natural Sciences
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Väitöspäivä
2022-09-09
Julkaisun pysyvä osoite on
https://urn.fi/URN:ISBN:978-952-03-2536-7
https://urn.fi/URN:ISBN:978-952-03-2536-7
Tiivistelmä
The increase in environmental awareness and stringent regulations from concerned governing bodies are the main driving forces for the growing interest in biomaterials. The development of environment-friendly bio-composites and their application in various industrial sectors has steadily increased during the last few decades. Wood-based, natural, and man-made fibres are used to manufacture bio-composites. The polymer matrix can be thermoset resins like epoxy (EP) or unsaturated polyester resin (UPR), or thermoplastic polymers like polypropylene (PP), polyethylene (PE) and polyvinyl chloride (PVC).
The primary resource to produce regenerated cellulose fibre (RCF) or man-made cellulose fibres is wood. The regenerated cellulose fibres, which are commonly named viscose or rayon, possess high purity, uniformity and reproducibility of their properties. Compared to lignocellulosic fibres, the benefit of man-made cellulose is that it is available in continuous filaments.
When it comes to the lignocellulosic fibre or regenerated cellulose fibre reinforced composites, the interface between fibre and matrix polymer plays a vital role. The hydrophilic wood-based fibres and hydrophobic thermoplastic polymer composites result in structurally weak composites due to the non-compatible interaction across the interface. Though the chemical modification techniques for wood fibre based composites are well-known, that of RCF-based composites requires more research. Few studies report the use of the chemical modification of viscose fabric to be used in composite production. The chemicals used in the modification step necessitate waste treatment, which involves extra energy consumption, time and money. Hence an environmentally friendly and sustainable approach to improve fibre-matrix adhesion is necessary.
In the Nordic countries with abundant raw material sources, the forest industry explores new applications for the produced side-streams. The building and construction, automotive and household commodities are the primary markets for wood-plastic composites (WPCs). By exploring new markets for WPC's, the composite industry and the forest industry will gain larger markets and better commercial profits from wood and its by-products. One approach for finding a new market for WPC's is to develop extrinsically conductive composites containing conductive fillers. The research in functionalising the WPC is in the developing stage, and it requires profound research.
This thesis aims to improve the interfacial adhesion in viscose fabric/thermoset resin-based composites by chemically modifying the viscose fabric. In another approach, the thermoset resin (epoxy resin) is modified with an appropriate silane coupling agent as an alternative to fibre surface modification, and its effect on various properties of composites is studied. Another objective of the study is to produce and characterise wood-plastic composites containing electrically and thermally conductive nanofillers. The effect of incorporating graphene nanoplatelets (GNP) on various properties of polypropylene-based WPC is studied. These types of composites can be a sustainable solution for the extrinsically conductive polymer market.
The silane coupling agents such as 3-aminopropyltriethoxysilane (APTES), 3-methacryloxypropyltrimethoxysilane (MPS) and also acetylation treatment are adopted to modify the viscose fabrics. The unsaturated polyester-based composites prepared from viscose fabric modified by APTES in ethanol medium increased the flexural strength and notched Charpy impact strength by 18% and 115%, respectively. The water absorption studies revealed that the APTES modification significantly delayed and reduced the total absorbed water compared to all other composites.
As an alternative to the fibre modification method, epoxy resin was modified by APTES to produce viscose fabric reinforced composites. The epoxide content determination and FTIR results from this study show that resin modification efficiency was better at 70oC compared to modification done at room temperature. The APTES was mixed directly into the epoxy resin, eliminating any process waste in the modification stage. The tensile strength and elongation at break of the composites prepared using APTES- modified epoxy resin increased by 14% and 41%, respectively. The Charpy impact strength of APTES-modified epoxy resin based viscose fabric composites increased by 115%.
The effect of GNP on various properties of WPC was studied. The addition of graphene into PP-based WPC yielded an anti-static/dissipative WPC compound at a graphene loading of 15 wt%. The surface resistivity of PP/wood/graphene composite decreased by several orders of magnitude from 1014 Q/sq to 106 Q/sq. While achieving the desired electrical properties, the tensile strength of hybrid WPC decreased by 25%. The thermal conductivity of WPC containing 20 wt% wood filler and 15 wt% GNP increased by 130% compared to WPC comprising 20 wt% wood filler.
The primary resource to produce regenerated cellulose fibre (RCF) or man-made cellulose fibres is wood. The regenerated cellulose fibres, which are commonly named viscose or rayon, possess high purity, uniformity and reproducibility of their properties. Compared to lignocellulosic fibres, the benefit of man-made cellulose is that it is available in continuous filaments.
When it comes to the lignocellulosic fibre or regenerated cellulose fibre reinforced composites, the interface between fibre and matrix polymer plays a vital role. The hydrophilic wood-based fibres and hydrophobic thermoplastic polymer composites result in structurally weak composites due to the non-compatible interaction across the interface. Though the chemical modification techniques for wood fibre based composites are well-known, that of RCF-based composites requires more research. Few studies report the use of the chemical modification of viscose fabric to be used in composite production. The chemicals used in the modification step necessitate waste treatment, which involves extra energy consumption, time and money. Hence an environmentally friendly and sustainable approach to improve fibre-matrix adhesion is necessary.
In the Nordic countries with abundant raw material sources, the forest industry explores new applications for the produced side-streams. The building and construction, automotive and household commodities are the primary markets for wood-plastic composites (WPCs). By exploring new markets for WPC's, the composite industry and the forest industry will gain larger markets and better commercial profits from wood and its by-products. One approach for finding a new market for WPC's is to develop extrinsically conductive composites containing conductive fillers. The research in functionalising the WPC is in the developing stage, and it requires profound research.
This thesis aims to improve the interfacial adhesion in viscose fabric/thermoset resin-based composites by chemically modifying the viscose fabric. In another approach, the thermoset resin (epoxy resin) is modified with an appropriate silane coupling agent as an alternative to fibre surface modification, and its effect on various properties of composites is studied. Another objective of the study is to produce and characterise wood-plastic composites containing electrically and thermally conductive nanofillers. The effect of incorporating graphene nanoplatelets (GNP) on various properties of polypropylene-based WPC is studied. These types of composites can be a sustainable solution for the extrinsically conductive polymer market.
The silane coupling agents such as 3-aminopropyltriethoxysilane (APTES), 3-methacryloxypropyltrimethoxysilane (MPS) and also acetylation treatment are adopted to modify the viscose fabrics. The unsaturated polyester-based composites prepared from viscose fabric modified by APTES in ethanol medium increased the flexural strength and notched Charpy impact strength by 18% and 115%, respectively. The water absorption studies revealed that the APTES modification significantly delayed and reduced the total absorbed water compared to all other composites.
As an alternative to the fibre modification method, epoxy resin was modified by APTES to produce viscose fabric reinforced composites. The epoxide content determination and FTIR results from this study show that resin modification efficiency was better at 70oC compared to modification done at room temperature. The APTES was mixed directly into the epoxy resin, eliminating any process waste in the modification stage. The tensile strength and elongation at break of the composites prepared using APTES- modified epoxy resin increased by 14% and 41%, respectively. The Charpy impact strength of APTES-modified epoxy resin based viscose fabric composites increased by 115%.
The effect of GNP on various properties of WPC was studied. The addition of graphene into PP-based WPC yielded an anti-static/dissipative WPC compound at a graphene loading of 15 wt%. The surface resistivity of PP/wood/graphene composite decreased by several orders of magnitude from 1014 Q/sq to 106 Q/sq. While achieving the desired electrical properties, the tensile strength of hybrid WPC decreased by 25%. The thermal conductivity of WPC containing 20 wt% wood filler and 15 wt% GNP increased by 130% compared to WPC comprising 20 wt% wood filler.
Kokoelmat
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