Renewable Composites Prepared from Biobased Thermoset Resins

Doctoral thesis, 2009

In our efforts to create a more sustainable society, several researchers have tried to prepare composites from renewable materials in recent years. The use of natural fibres for reinforcement of composites has been relatively well studied. To date, most studies of natural fibre-reinforced composites have either involved the use of conventional thermoset resins or thermoplastic biopolymers. While there are currently several thermoplastic polymers on the market that are produced from renewable resources, thermosets are inevitably produced from petroleum resources. The development of biobased thermoset resins is therefore of considerable importance. Such resins could be used in future for composite applications, for coating applications or in adhesives. This thesis describes the development of biobased thermoset resins for composite applications. Thermoset resins were synthesised from both epoxidised soybean oils as well as from lactic acid. These resins have been characterised neat as well as together with various reinforcements. The main objective has been to study these biobased resins together with natural fibres for reinforcement, though to some extent nano-reinforcements and glass fibres have also been used as reinforcements. Natural fibre-reinforced composites were prepared from several different biobased thermoset resins. Resins based on soybean oil as well as a resin based on lactic acid were evaluated. The soybean resins were prepared by introducing acrylate or methacrylate groups into the molecules of soybean oil. The second type of thermoset resin used was based on lactic acid. This resin consists of star-shaped methacrylated oligomers of lactic acid. Natural fibres were impregnated by several impregnation techniques. Composites were prepared from the biobased resins together with various natural fibres, such as flax and hemp fibres. The resulting composites were evaluated by tensile testing, flexural testing, impact testing, DMTA and SEM. The results show that composites prepared from biobased resin have relatively good mechanical properties and can be used for indoor applications such as furniture and construction elements.