Papers by Author: Pranee Chumsamrong

Abstract: The aim of this work was to investigate the effects of fiber architecture and fiber surface treatment on flexural and impact properties of woven sisal fiber/epoxy composites. The woven sisal fibers with three different weave types including plain weave (P-weave), harness satin weave (S-weave) and right hand twill weave (R-weave) were used. For untreated fiber/epoxy composites, the fiber contents in the composite were 0, 5, 10 and 15% by weight (%wt). The untreated S-weave sisal fiber/epoxy composites showed the best overall properties and the composites with 15% fiber loading showed the highest properties. When compared to pure epoxy, flexural strength, flexural modulus and impact strength of the composite with 15% wt fiber increased by 4.5%, 60.6% and 150% respectively. Therefore, the composite of 15% wt silane treated S-weave and epoxy was prepared in order to study the effect of fiber surface treatment. The results showed that the composite containing 15% wt silane treated fiber possessed nearly the same properties with the untreated fiber/epoxy composite.

Abstract: In this work, hydroxyl-terminated lactic acid prepolymer was firstly prepared by adding diethylene glycol in the condensation of lactic acid. Molecular weight, acid value and structure of prepolymer were characterized. The results showed that the prepolymer was hydroxyl-terminated with weight average molecular weight (M_W) of 10,000 g/mol. After that, the chain linking polymerization of the prepolymer was carried out in a glass tube at 160 °C for 1 h employing 1,6-hexamethylene diisocyanate (HMDI) as a chain extender. By varying the hydroxyl/isocyanate ratio, it was found that the OH/NCO ratio of 1:2 seemed to be the most suitable ratio which gave PLA with the maximum M_W of 93,000 g/mol.

Abstract: From our previous study, natural rubber (NR) was used to improve toughness of poly (lactic acid) (PLA). Impact strength and elongation at break of PLA was increased when adding NR. Moreover, by using NR-g-GMA as compatibilizer for PLA and NR blend, impact strength and elongation at break was improved. However, tensile strength and modulus of PLA/NR blend with and without NR-g-GMA were decreased. In this study, calcium carbonate (CaCO₃) and vetiver grass fiber were used as fillers in PLA/NR blend. With the addition of CaCO₃ into PLA/NR blend with NR-g-GMA, impact strength and modulus of the composite were further increased with a loss in tensile strength. In contrast, the addition of vetiver grass fiber into PLA/NR blend with NR-g-GMA led to an increase in tensile strength and modulus and a decrease in impact strength and elongation at break. The onset degradation temperatures of PLA composites were lower than that of PLA and PLA/NR blend.

Abstract: In the present work, bisphenol-A based epoxy resin was blended with methyl methacrylate (MMA)/glycidyl methacrylate (GMA) grafted depolymerized natural rubber (GDNR). GDNR/epoxy resin blend was composite with woven sisal fiber. GDNR was prepared by solution grafting MMA/GMA (90/10 w/w%) onto depolymerized natural rubber (DNR). The occurrence of GDNR was confirmed by proton nuclear magnetic resonance spectroscopy (¹H-NMR). Amount of GDNR in the blend was 1 part per hundred resins. Impact strength of epoxy resin was increased by 62% when GDNR was added. Composites of GDNR/epoxy resin and woven sisal fiber were prepared by hand-lay up process. Amounts of woven sisal fiber in the composite were 3, 5 and 7% by weight (wt%). The flexural modulus of the composites was higher than that of neat epoxy resin and increased with increasing amount of woven sisal fiber. Nevertheless, flexural strength of all composites was lower than those of neat epoxy resin and the blend. Compared to neat epoxy resin, the impact strength of the composite containing 7 wt% woven sisal fiber was further increased to 114%.

Abstract: Highly crosslinked epoxy resin for engineering applications is normally stiff but brittle. Therefore, many attempts have been made to improve its toughness. Nowadays, several studies have been done on toughening epoxy resin using natural rubber (NR) because it is abundant and comes from renewable resource. In the present work, NR was subjected to depolymerize in order to achieve molecular dispersion of NR in epoxy matrix. Depolymerized natural rubber (DNR) was prepared by adding a carbonyl compound to natural rubber latex solution and subjecting the mixture to air oxidation in the presence of a radical forming agent at 70°C. In addition, the interfacial adhesion between rubber and matrix must be present to achieve a significant increase in toughness. Hence, DNR was further functionalized by grafting with monomer mixture of methyl methacrylate (MMA)/glycidyl methacrylate (GMA) (90/10 wt/wt%) in an amount of 50% based on rubber content. Solution polymerization was used to graft such monomers using 2 hours reaction times at a reaction temperature of 80oC. Two types of initiator used were benzoyl peroxide (BPO) and azo-bisisobutyronitrile (AIBN). The amounts of initiator in the grafting process were 1, 2, and 3 parts per hundred of DNR. Effects of type and concentration of initiator on grafting efficiency of MMA/GMA monomer mixture onto depolymerized natural rubber were studied by proton nuclear magnetic resonance (1H-NMR) analysis. The molecular weight of DNR was characterized by gel permeation chromatography (GPC). The results indicated good evidence for the formation of graft co-polymers in the presence of both initiators, AIBN or BPO. However, the amounts of grafted MMA/GMA on DNR backbone using BPO was higher than those on DNR backbone using AIBN.

Abstract: In order to increase polarity and widen application of natural rubber, the natural rubber (NR) was modified by graft copolymerization with methyl methacrylate (MMA) and glycidyl methacrylate (GMA). The grafting reaction was carried out using emulsion polymerization at 40°C. Redox initiator was used to initiate polymerization. Weight percentage ratio of MMA to GMA was firstly fixed at 90/10 in order to study the effects of amount of initiator and monomer mixture-to-rubber ratio on grafting efficiency [GE(%)] and percentage conversion of monomer (%conversion). The graft copolymerization condition that showed the highest grafting efficiency was chosen to study the effect of MMA-to-GMA ratio. It was found that the highest grafting efficiency [GE(%) = 85.11] were obtained when 1 part of NR, 0.75 part of monomer mixture and 1 phr of initiator were used. 1H-NMR spectrum of the graft copolymer with grafting efficiency of 85.11% illustrated that main monomer grafted onto NR chain was MMA. However, there was a signal of GMA that attached onto the NR chain. The results from an adjustment of MMA-to-GMA ratio showed that grafting efficiency tended to decrease with increasing the amount of GMA. On the other hand, an adjustment of MMA-to-GMA ratio did not significantly affect %conversion.

Abstract: Polylactic acid (PLA) and natural rubber (NR) were melt blended with vetiver grass fiber using an internal mixer. Heat treatment at the temperature of 180°C was done to obtain heat treated vetiver grass fiber. Glycidyl methacrylate grafted natural rubber (NR-g-GMA) was used as a compatibilizer of PLA/vetiver/NR composites. The injection molding and compression molding were used to prepare the specimens. Molecular weight determination of PLA before and after processing was done by Gel Permeable Chromatography (GPC).Comparisons between the mechanical properties of the composites prepared from injection molding and compression molding were made.

Abstract: In this study, the effects of weave type and fiber content on the physical properties of woven sisal fiber/epoxy composites were investigated. Sisal fibers used in this work were obtained from Nakhon Ratchasima, Thailand. Both untreated and alkali-treated fibers were employed. The woven sisal fibers were manufactured by hand weaving process. The fiber content in sisal fiber/epoxy composites were 3 wt.%, 5 wt.% and 10 wt.%. The composites were cured at room temperatures. In order to determine mechanical properties of the composites, flexural and impact tests were applied. Flexural strength and flexural modulus of all composites were higher than those of pure epoxy resin and tended to increase with increasing fiber content. The impact strength of all composites was lower than that of pure epoxy resin. The composites containing 10 wt.% sisal fibers showed the highest impact strength. There was no definite influence of weave type on flexural properties of the composites. At 3 and 5 wt.% fiber, the composites containing plain weave fibers seemed to show a higher impact strength than the composites containing other weave types.

Abstract: In order to study the potential of increasing the weather stability of natural rubber latex for use as a water-based contact adhesive, the natural rubber latex was modified by graft copolymerization with n-butyl acrylate (BA) and methyl methacrylate (MMA). The grafting reaction was carried out using emulsion polymerization at 60°C. Potassium persulfate was used to initiate polymerization. Four different weight percentage ratios of BA to MMA used in this work were 80:20, 70:30, 60:40 and 50:50. Percentage conversion of the monomer of all latexes prepared was ≥ 79.8 %. The grafting efficiency of grafted natural rubber latexes with a different monomer ratio tended to decrease with an increase of MMA. The adhesion property was characterized by 90° peel strength and 180° lap shear tests. The shear strength value of grafted natural rubber latexes increased with an increase of MMA content. The grafted latex with the monomer ratio of 50:50 possessed higher shear strength than natural rubber latex. The peel strength value of grafted natural rubber latexes seemed to lower than that of natural rubber latex. The weather stability of the modified latex was characterized using thermogravimetric analysis (TGA) and also the peel samples were left in the open air for 45 days before testing. The results showed that grafted natural rubber latex had a higher weather stability than natural rubber latex.