dc.description.abstract |
Composites have widely been used in the past due to its attractive characteristics in terms
of high strength in relation to weight. However, they have been derived from petroleum
products which are difficult to dispose. Environmental issues and awareness globally has
attracted much research into the development of sustainable composites.
Polylactic Acid is sugar based biodegradable polymer and possesses attractive properties
that makes it a suitable polymer material for sustainable composites production. However,
there arc other properties that limits its application and include: low thermal stability.
reduced mechanical performance compared to polypropylene, polyethylene and
polystyrene. This study therefore aims at preparation, characterization and comparison of
PLA biodegradable composite from Kraft cellulose, wood fiber, Lyocell cellulose and
Viscous cellulose with and without Desmodur as a copolymer.
In the study, properties of PLA were improved by compounding and hot pressing it with
different natural commercial and readily available fibers of Kraft cellulose, wood fiber,
viscose, Lyocell® and Cordenka® in mass proportions of l 0%, 20% and 30% relative to
the matrix PLA with 10% of an additional copolymer. Charpy impact strength, tensile
strength, thermal properties and morphology were investigated and compared for all
composites and their possible applications. It was found that Charpy impact strength
reduced with increase in fiber content with highest impact of (63 kJ/m2) at 10% viscose
fiber loading. A high tensile strength of 67 MPa was obtained from 30% Lyocell fiber in
the composite which was 4 MPa and 10 MPa higher than that of Kraft cellulose at the 30%
fiber loading and pure PLA respectively. Modulus of elasticity reached a maximum value
of 6 GPa at 30 % loading of Kraft cellulose. Addition of copolymer showed reduced
stiffness for all the composites due to impregnation of the active sites instead of bonding hence did not improve the fiber-matrix interaction. Scanning electron micrographs of the
fractured surface showed better fiber-matrix interface, fiber pullout and the active role
played by fibers in absorbing energy thus enhancing the mechanical properties. Water
absorption on the other hand showed prolonged water uptake. Thermal analysis for
composite without copolymer revealed a stable crystal structure whereas those with
copolymer showed different melting peaks indicative of the presence of different phases in
the structure. The results obtained show that the properties of PLA can be enhanced by
addition of natural fibers in cellulosic form such as Kraft cellulose, Lyocell and Viscose
cellulose. The contribution of this research in practice it the cost reduction associated with
blend of expensive PLA with commercial readily available cellulose fibers which reduces
the cost of these composites and expected to open up an avenue in which these
biodegradable composites can be utilized in this applications to replace the components
made from non-biodegradable polymers. Scientifically, the application of copolymer-
Desmodur, a blocked polyisocyanate stable at room temperature and dissociates to
regenerate isocyanate functionality when heated to 160° C, easily reacting with terminal
both hydroxyl and carboxyl group present in PLA and Cellulose fiber at melting
temperature of PLA. This resulted in a new ductile material, with good interface between
matrix and cellulose fibers. |
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