Microwave and thermally cured natural fiber epoxy composites

Lignocellulosic natural fibers such as henequen, flax, hemp, and kenaf have many properties which make them an attractive alternative to traditional reinforcement materials such as glass, carbon, and aramid. In this study, research was performed in two sections. The first phase utilized conventional oven curing and single mode heating for microwave processing and untreated fibers for composite reinforcement material. Using this heating method, the size of the composites was restricted to very small samples. The second phase used variable frequency mode switching to cure larger samples with microwave heating. Fibers treated with alkali and silane were used in addition to untreated fibers. Modeling of the epoxy curing process was also conducted.;Single mode heating was used first to make small composite samples. These composites were examined using differential scanning calorimetry, dielectric testing, and thermogravimetric analysis. Untreated flax, henequen, hemp, and kenaf were used in this section of the study. Additionally, epoxy compatible glass was used for comparison. Equivalent composites were also made with oven curing.;Variable frequency microwave heating utilizes complementary heating modes to cure larger composites. In this section, alkali and silane treatments were applied to kenaf and hemp fibers. The fibers and composites were examined using FTIR, XPS, water absorption testing, ESEM, and flexural testing. Following are some important findings from this research. Alkali treatment removes hemicellulose and lignin from fiber surfaces. Alkali treated hemp and kenaf composites absorb more water than other treated fiber composites. The silane treatment is effective in increasing the adhesion between the fiber and matrix.;Microwave processing of natural fiber composites has not been previously examined in literature. Natural fiber reinforced epoxy composites can be cured 75 minutes faster in the microwave than in the oven. The dielectric properties of natural fibers were studied and compared to the dielectric properties of glass fibers. It was found that the dielectric loss factors of all the fibers were similar, so all the fiber composites examined should interact with microwaves in a similar manner. This was confirmed with the DSC experiments. More work needs to be done on applying pressure to the natural and glass fiber reinforced composites to produce composites of higher quality using microwave curing.