Suteera Witayakran

One-pot synthesis of 1,4-naphthoquinones and related structures with laccase

The one-pot synthesis of 1,4-naphthoquinones by the Diels–Alder reaction of dienes with para-quinones generated in situ with laccase (EC 1.10.3.2, p-diphenol:dioxygen oxidoreductase) in an aqueous medium was developed in this study. The para-quinones were generated in situ by the laccase oxidation of the corresponding 1,4-hydroquinones and subsequently underwent the Diels–Alder reaction with dienes, and further oxidation to finally generate 1,4-naphthoquinones, in good yields. This reaction methodology provides unique green chemistry synthesis for isolation of the naphthoquinones, and without relying on organic solvents or hazardous heavy metal reagents. In this paper, the effects of laccase dose, temperature, and substrate sensitivity on the overall reaction were investigated.

Mechanical Properties of All-Cellulose Composites Made from Pineapple Leaf Microfibers

Pineapple leaf microfibers were firstly prepared using steam explosion, and all-cellulose composites were subsequently prepared using a surface selective dissolution process with the solvent of lithium chloride and N,N-dimethylacetamide (LiCl/DMAc). Mechanical properties and surface morphology of all-cellulose composites with immersion times of pineapple leaf microfibers in the solvent of LiCl/DMAc were investigated using tensile testing and scanning electron microscopy, respectively. The tensile strength of the all-cellulose composites with 120 min-immersion time was approximately 28 times higher than that of the pineapple leaf microfiber mats. These biocomposites made from pineapple leaf microfibers could be one of the potential alternatives to replace glass fiber reinforced composites.

Development of Oil Palm Empty Fruit Bunch Fiber Reinforced Epoxy Composites for Bumper Beam in Automobile

This research aims to use oil palm empty fruit bunch (EFB) fibers to reinforce epoxy resin for bumper beam in cars to replace epoxy/glass fiber composite. EFB fibers were extracted by two methods; chemical method by treating with 10-30% sodium hydroxide (% by weight of fiber) and mechanical method by steam explosion process at 12-20 kgf/cm2 for 5 mins. Then, the obtained fibers were bleached by hydrogen peroxide. The results show that the chemical method can eliminate lignin better than the other and provided stronger fibers. Increasing of alkaline concentration yielded the decrease of lignin content and increase of cellulose content, while no significant difference on fiber size and strength was observed. In steam explosion method, increasing of pressure vapor affected to more dark brown color and disintegrated fibers. Therefore, the optimal method for preparing EFB fibers for reinforcement of epoxy composite was chemical treatment using 30%NaOH, followed by bleaching. Then, the EFB fibers extracted by chemical method at 30%NaOH were used for reinforcing epoxy composite with fiber contents of 0-10%w/w and compared to epoxy/glass fiber composite. The results show that flexural modulus did not increase with increasing fiber content. However, the chemical treated fibers can support composite from falling apart after testing like glass fiber reinforced composite with fiber contents upper than 7.5%w/w. Impact strength and storage modulus of alkaline treated palm fiber reinforced composites increased when fiber content more than 7.5%w/w. Thermal properties of composite, analyzed by DSC and DMTA, shows that the Tg increased with fiber content. Flexural modulus and thermal properties of EFB reinforced epoxy composites provided similar results to glass fiber reinforced composites. Therefore, EFB fiber reinforced epoxy composite could be an alternative green material for bumper beam in automobile.

All-cellulose composite laminates prepared from pineapple leaf fibers treated with steam explosion and alkaline treatment

Pineapple leaf fibers with diameters of 43 ± 0.1 µm were treated by two different approaches: the alkaline treatment and the combination of the steam explosion and alkaline treatment. The observations revealed the steam explosion process efficiently provided 3.4 µm diameter fibers with a less amount of lignin and a higher proportion of cellulose, compared with the alkaline-treated fibers. The steam-exploded fibers showed higher crystallinity and more thermal stabilities than the alkaline-treated fibers. No structural change from cellulose I to cellulose II was detected from both treated pineapple leaf fibers. Subsequently, all-cellulose composite laminates were prepared from these two types of treated pineapple leaf fibers mats. The higher tensile strength and modulus were obtained from the steam-exploded pineapple leaf fibers composite laminates due to larger surface areas of the fibers interacted with the cellulose matrix. Fracture morphology of the composites was studied after tensile deformation. The combination mechanism of fiber breakage and fiber pull-out deformation was observed from the steam-exploded pineapple leaf fibers composite laminates, whereas only fiber pull-out mechanism was found from the alkaline-treated pineapple leaf fibers composite laminates. The fiber width and amounts of the matrix filling in pores in a mat were found to dominate the mechanical properties of the all-cellulose composites.