his research work aimed to study the effects of the addition of sisal fiber and surface treatment by epoxy silane on the physical and thermal properties of polylactic acid (PLA). Specimens of PLA and unidirectional fiber-reinforced composite were processed by a compression molding machine and evaluated the physical and thermal properties by water absorption measurement and differential scanning calorimetry (DSC) analysis respectively. The result showed that water absorption tended to increase by adding sisal fiber whereas surface treatment of sisal fiber by epoxy silane improved water resistance of composites. The water absorption values at immersion time of 5 days were 0.89 1.13 and 1.26 % for PLA PLA/treated sisal fiber composite and PLA/untreated sisal fiber composite respectively. For thermal properties the addition of sisal fiber led to decreases in glass transition temperature and crystallinity. These were because the presence of continuous fiber might interfere with the crystallization of PLA. The surface treatment of continuous fiber with epoxy silane led to difficult crystallization. The good interfacial adhesion interrupted PLA alignment.

This research was concentrated on characterized mechanical properties and adjusted compatibility of poly (lactic acid) (PLA) with thermoplastic starch (TPS) as biodegradable polymers composites. PLA was blended with TPS at the proportion of 10 20 30 50 and 70 wt% as well as 2 phr chain extender by an internal mixer at 200°C. The blended materials were then injection molded at 230°C. Tensile testing showed that as the amount of TPS increase the elongation at break tended to increase but the tensile strength and modulus tended to decrease. The morphology was investigated by scanning electron microscope. It was found that distinct phase between PLA and TPS was observed. Yet adding the chain extender clearly improved the compatibility between PLA and TPS. The blended materials were also analyzed by differential scanning calorimetry method to study thermal properties. It was found that as the amount of TPS increased the glass transition temperature (Tg) melting temperature (Tm) and cold crystallization temperature (Tcc) deceased. Additionally chain extenders did not affect thermal properties. The thermal stability of the composites decreased when increasing the amount of TPS because of the degradation of TPS in PLA. However when heated at 100ºC for 1 hr the PLA sample bent while TPS did not bend. When PLA was mixed with TPS the composite was bent according to adding TPS.

This research work was to study the toughening modification of polylactic acid by the mixing with epoxidized natural rubber (ENR) and the increase of effectiveness of mechanical properties with a compatibilizer. Enhancement of properties in polylactic acid was evaluated by tensile and impact testings Fourier-transform Infrared Spectroscopy (FTIR) technique Differential Scanning Calorimetry (DSC) technique and Scanning Electron Microscope (SEM). For the addition of ENR it was revealed that the increase of ENR contents improved elongation at break and impact strength but decreased tensile modulus and ultimate tensile strength. Glass transition temperature (Tg) percentage crystallinity and the melting point of polylactic acid tended to decrease with the addition of ENR. Chemical change was found that position of C=O peak in polymer blend was slightly shifted as compared to the spectrum of neat polylactic acid. The optimum formulation for toughening modification was ENR content of 30 wt%. Its impact strength was 1982.55 % of neat polylactic acid. For increasing effectiveness of mechanical properties with a compatibilizer it revealed that the addition of Joncryl ® ADR-4300 as compatibilizer improved both tensile and impact properties. The optimum loading of a compatibilizer for improving mechanical properties was 0.5 wt% of polylactic acid. The decreases of crystallinity and melting point of polylactic acid with adding Joncryl ® ADR-4300 might be because Joncryl ® ADR-4300 was also chain extender of polylactic acid and it might be obstructing crystallization. The presence of Joncryl ® ADR-4300 unaffected on Tg value and chemical change.

This research work was to study the improvement of toughness of polylactic acid (PLA) and the cost reduction of raw material with addition of untreated and treated oil palm fiber (OPF). The detail of this work was divided into two parts. The first was to find the suitable condition for surface treatment of OPF with sodium hydroxide (NaOH). The second part was to study the effect of untreated and treated OPF contents on the mechanical properties of PLA. For surface treatment of OPF NaOH concentrations and immersion times were varied from 0 to 15 wt% and 0 to 30 min respectively. Aspect ratio (L/D) and surface of untreated and treated OPF were investigated by using optical microscope and scanning electron microscope (SEM) respectively. The result suggested that the most suitable condition for surface treatment of OPF was NaOH concentration of 10 wt% at immersion time of 20 min. Treated OPF was occurred microporous and had more rough as compare to untreated fiber. For the effect of untreated and treated OPF contents on the mechanical properties of PLA it was evaluated by tensile and impact testing. SEM was used for investigation of interfacial adhesion and fiber dispersion. The results showed that tensile modulus and impact strength tend to increase with adding 2.5 wt% OPF content and slightly changed at higher OPF content whereas ultimate tensile strength and elongation at break decreased with increasing fiber content. Surface treatment with NaOH led to enhancement of mechanical properties of composite due to improve interfacial adhesion and fiber dispersion.

This study focused on screening and identification of lactic acid bacteria with antimicrobial activity against Escherichia coli from milk samples. There were 250 isolates showing different antimicrobial activities. Five isolates with predominant anti-E. coli efficiency were chosen for the study of bacteria identification bacterial growth as well as the stability in pH change heating and proteolytic treatment. The sequences of 16s rDNA indicated that selected isolates were Lactobacillus sp.. The antimicrobial efficiency described in the term of Antimicrobial Index (AI) ranged from 0.63 to 0.84. However the anti-E coli activity did not change when performing the test under proteinase-treated condition and high temperature-treated condition. Conversely the pH adjustment of cell-free bacterial culture to 7.0 demolished their antimicrobial activity. This data implied that their antimicrobial activities were results of acidic condition produced by lactic acid bacteria. From this study the selected lactic acid bacteria showed their potential as a starter culture for fermented foods.