Amornrat Lertworasirikul

Pomelo (Citrus maxima) Peel-Inspired Property for Development of Eco-Friendly Loose-Fill Foam

For development of eco-friendly packaging foam from pomelo peel, physical and mechanical properties of the pomelo peel and effects of pomelo varieties, namely Kao-Nampueng, Thong-Dee, and Kao-Pan, on their properties were investigated. It was found that the pomelo variety showed somewhat significant effect on physical and mechanical of pomelo peel properties. Because of its thick peel with high moisture content (75-80%) and water activity (0.90-0.98), the peel weight accounted for almost half of the total fruit weight. Cell structure and pore size of the peel were examined using the environmental scanning electron microscope (ESEM). The result showed an open cell foam structure with pore size of approximately 151±31 µm. The pore size was more open and large towards the outer surface. Uniaxial compression tests on pomelo peel samples with and without flavedo showed good reproducible stress-strain curves despite its biological variation. Young’s moduli of both samples were calculated to be 200-300 kPa and 110-210 kPa, respectively. Moreover, the most important property of packaging foam is the ability to absorb energy during impact which can be characterised through the measurement of the onset strain of densification. It was found that the strain values at the maximum energy absorption efficiency (εcd) of peel samples with and without flavedo for all studied pomelo varieties were comparable and were approximately in the range of 60-65%. These preliminary results indicate very promising mechanical properties of pomelo peel as eco-friendly packaging foam although further modifications are required to improve their physical and shelf-stability properties.

Effect of Poly(Hexamethylene Succinamide) on Crystallization of Poly(L-Lactic Acid)

Poly(L-lactic acid) (PLA) has good mechanical properties and is biodegradable. However, its crystallization rate is slow, crystallization period long, and its crystallization temperature high at 116 °C. Consequently, long processing cycles are required for the production of high crystallinity poly (L-lactic acid). Addition of nucleating agents is an efficient way to solve this problem. Aliphatic amide such as N,N-ethylenebis(12-hydroxystearamide) and ethylenebis-stearamide are reported as nucleating agents for poly (L-lactic acid). In this study, the effect of the aliphatic polyamide, poly (hexamethylene succinamide) on the crystallization behavior of PLA was investigated. Poly (hexamethylene succinamide) was synthesized by melt polymerization. Between one and ten weight percent poly (hexamethylene succinamide) was blended with poly (L-lactic acid) by melt extrusion. The crystallization temperature and crystallization period decreased with increasing poly (hexamethylene succinamide) content. The degree of crystallinity increased with the addition of poly (hexamethylene succinamide). A poly (hexamethylene succinamide) content of 5%wt provides optimum conditions for production of poly (L-lactic acid)-poly (hexamethylene succinamide) blend with good mechanical properties. The polymers obtained are entirely from renewable resources.

Effect of Poly(D-Lactic Acid)-co-Polyethylene Glycol on the Crystallization of Poly(L-Lactic Acid)

Poly (lactic acid) (PLA) is a biopolymer derived from renewable resources and can be disposed of without creating harm to the environment. PLA can be formed by thermoplastic processes and has good mechanical properties. However, its disadvantages are a high crystallization temperature, slow crystallization rate, poor heat stability and low ductility. In the past, it was found that poly (D-lactic acid) (PDLA) can form complexes with poly (L-lactic acid) (PLLA) and the complexes could accelerate the crystallization and increase the degree of crystallinity of the PLA, but decrease the ductility. It is known that polyethylene glycol (PEG) can improve the ductility of PLLA. In this research, PDLA was copolymerized with PEG in an attempt to improve both crystallization behavior and ductility of PLLA. Poly (D-lactic acid)-co-polyethylene glycol (PDEG) was synthesized by ring opening polymerization using D-lactide and PEG at a D-lactide:PEG weight ratio of 10:3. The PDEG was blended with PLLA with a PDEG content of 0wt% to 50wt% by melt blending process. Fourier transform infrared spectrometry (FT-IR) and X-Ray diffractometry (XRD) confirmed the stereocomplex formation between PDEG and PLLA. Characterization by differential scanning calorimetry (DSC) revealed that crystallization temperatures of the blends were decreased in the presence of PDEG. Storage moduli and tan of the blends obtained from dynamic mechanical analysis (DMA) decreased as PDEG content increased. Polarized optical microscopy (POM) micrographs of blends with PDEG content of 1wt% to 5wt% obviously showed that crystallization rate was increased. PDEG has the potential to be an effective nucleating agent and efficient plasticizer for PLLA.

Investigation of Synthesis Parameters for Modification of Chitosan with Enrofloxacin

This research aims to investigate synthesis parameters for modification of chitosan with enrofloxacin. Most modifications of chitosan are focused on amino group. There are many methods for modification of chitosan, for example, conjugation of amino group with carboxylic group by coupling agents. 1-Ethyl-3-(3-(dimethylamino) propyl) carbodiimide hydrochloride (WSC) and N-hydroxysuccinimide (NHS) are widely used coupling agents for amide formation under mild conditions. Those two coupling agents were applied in this study. Optimum amount and ratio of coupling agents, amount of enrofloxacin and reaction times were investigated. The chemical structures were characterized by Fourier transform infrared spectroscopy (FT-IR). The optimum synthesis conditions were determined from the absorbance ratios. Chitosan-enrofloxacin has antibacterial activity against both S. aureus and E. coli.

Regulating surface wettability of PEO/PLLA composite electrospun nanofibrous membrane for liquid phase filtration

The PEO/PLLA composite nanofibrous membranes were prepared by electrospinning technique for liquid phase filtration application. In this experiment, PLLA homopolymer and PLLA-PEG copolymer were added into PEO solution to increase hydrophobicity of nanofibrous membrane surface. PLLA content was fixed at 30% by weight of total solid. Morphology and fiber diameter were characterized from scanning electron microscope (SEM) images. Fiber diameters of PEO/PLLA homopolymer and PEO/PLLA-PEG copolymer are 582±78 nm and 657±167 nm, respectively. Surface wettability property of PEO/PLLA composite nanofibrous membranes were measured by apparent water contact angle. The apparent water contact angle value of PEO/PLLA is 120°±2°, while PEO/PEG-b-PLLA is 99°±7°. The surface wettability of PEO/PLLA composite nanofibrous membranes can be modified by varying type of polymer.