Atitsa Petchsuk

Controlled-Release Materials for Fertilizer Based on Lactic Acid Polymers

ontrolled-release materials for urea are prepared by spray coating urea granulates with lactic acid based homo- and co-polymers solutions. Percent coating as a function of polymer types, molecular weight, polymer concentration, and dose applications are examined by gravimetric analysis. Percentage of urea dissolution in water of the coated fertilizer is measured by monitoring refractive index of the solutions. Morphology of the polymer coating surfaces is revealed by Scanning Electron Microscopy (SEM). It was found that an amount of cracks and pin-holes, which is dependent on polymer types and molecular weight, plays a significant role in controlling the rate of urea release. Results from urea dissolution test also suggests that the synthesized poly(lactic acid-co-ethylene terephthalate) show urea-holding efficiency comparable to that of commercial PLA, despite its much lower molecular weight, indicating that the copolymer is potentially suitable for this specific application.

Polylactic acid glycolysate as a cross-linker for epoxidized natural rubber Effect of cross-linker molecular weight

Hydroxyl-capped polylactic acid (PLA) oligomers are prepared by glycolysis reaction of PLA with ethylene glycol (EG) and used as a macromolecular cross-linker for epoxidized natural rubber (ENR). The glycolyzed PLA (GPLA) with three different molecular weights (2000, 10,000, and 44,000 g mol−1) are prepared by varying the glycolysis conditions. Effects of GPLA chain lengths and GPLA/ENR feed ratios on cross-linking efficiency, chemical structures, and physical properties of the cured products are investigated. The cross-linking efficiency is examined using a moving die rheometer, solvent fractionation, thermogravimetric analysis, and Fourier transform infrared spectroscopy. Optimum GPLA/ENR compositions for the curing reaction range from 20 wt% to 33 wt%, depending on the GPLA chain length. Because of their biodegradability, biocompatibility, and the ability to tune up their structures and properties, the cured rubber materials have high potential for use in various biomedical applications.

Synthesis and Characterizations of PLLA/PEG Block Copolymers

Poly(lactic acid-co-ethylene glycol) (PLLA/PEG) copolymers were synthesized and their properties were characterized. The PLLA/PEG/PLLA triblock copolymers were synthesized by ring-opening polymerization from l-lactide (LLA) and PEG macroinitiator. Stannous octoate, Sn(Oct)2 was used as a catalyst. Effects of molecular weight of PEG (600, 2000 and 4000), LLA/OH molar ratios (95:5, 98:2) and a sequence of addition of the reactants on properties of the copolymers were investigated. The triblock copolymers were subsequently used in a production of multiblock copolymers by reacting with a chain-extending agent, hexamethylene diisocyanate (HMDI). Chemical structure and molecular weight of the copolymers were characterized by 1H-NMR, FTIR and GPC. The results showed that molecular weight of triblock copolymers varied from 4,500 to 10,200. After chain extension, multiblock copolymer with molecular weight of 16,490 was produced. Thermal properties of the copolymers were also examined by DSC.

Synthesis and Characterization of Degradable Poly(Ethylene Terephthalate-co-Lactic Acid) and its Blends

Because of their respective advantages, the combination of good material properties of poly(ethylene terephthalate) (PET) and degradability of polylactic acid (PLA) is researched as degradable copolymer for packaging and agricultural applications. Poly(ethylene terephthalate-co-lactic acid) (PET-co-PLA) has been synthesized by employing polycondensation of mixtures of dimethyl terephthalate (DMT), lactic acid (LA) and ethylene glycol (EG), using tin(II) octoate as a catalyst. A chain-extending reagent, hexamethylene diisocyanate (HMDI), was then used in the subsequent step to increase the chain length of the copolymer and improve its mechanical properties for suitable applications. The chemical structure and molecular weight of the copolymers were investigated by FTIR, NMR, and DSC. NMR results indicated the incorporation of lactic acid and PET units in the copolymer chain. Additionally, blends of the resulting copolymer with commercially-available PLA were studied. The blend miscibility was examined by DSC and FTIR spectroscopy.

Preparation and Properties of Electrospun Fibers of Titanium Dioxide-Loaded Polylactide/Polyvinylpyrrolidone Blends

Nanofibers of polylactide (PLA)/polyvinylpyrrolidone (PVP) blends loaded with titanium dioxide (TiO2) particles have been prepared by an electrospinning technique. TiO2 particles are formed by sol-gel mechanisms from titanium (IV) iso-propoxide (TTIP) precursor. Effect of TiO2 formation rate on properties of the fibers are examined by adding iso-propyl alcohol (iPOH) to slow down the TiO2 precipitation process. The use of iPOH produces fiber mats consisting of slightly bigger and smoother filaments, but smaller-sized embedded TiO2 particles. Both materials show a distinct UV absorption characteristic of TiO2 at λmax 300 nm, which can be applied in catalytic applications. Degradation behaviors of the materials in phosphate buffer solutions have also been investigated. The materials have high potential for use as epoxidation catalysts for conversion of vegetable oils to polymeric building blocks and plasticizers.

Preparation and Characterizations of Electrospun Lactide-Based Polymeric Nanofibers

Poly(L)lactide (PLLA), aliphatic polyester, and poly(LLA-co-DLLA) copolymers consisting of 2.5, 7.5, 50% of DLLA content were also synthesized. PLLA was successfully electrospun by using 15wt% solution in (1DMF:3CHCl3) mixed solvent. 2.5, 7.5, 50% P(LLA-co-DLLA) copolymers were then spun at 8, 10, and 15wt% concentration in a single chloroform solvent, respective. The lactide-based polymeric nanofibers were characterized by Scanning Electron Microscope (SEM). Smooth surface morphology was observed in nanofibers produced from PLLA and 50% P(LLA-co-DLLA) copolymer. However, surface porosity was observed in the corresponding fibers from 2.5 and 7.5% P(LLA-co-DLLA) copolymers. These nanofibers have high potential for wide range of applications such as filter media, nano-sensor, drug delivery and tissue scaffold, especially, those derived from 2.5 and 7.5% P(LLA-co-DLLA) copolymers which contain high degree of porosity.

Synthesis and Characterization of PLA-Based Aliphatic-Aromatic Copolyesters: Effect of Diols

PLA-based aliphatic aromatic copolyesters have been synthesized and characterized in order to incorporate the degradability of PLA and good mechanical properties of aromatic species. Synthesis of the copolymers was conducted by polycondensation of lactic acid with dimethyl terephthalate (DMT) and various diols using stannous(II) octoate as a catalyst. Three types of diols with different methylene lengths were employed, i.e., ethylene glycol (EG), propylene glycol (PG) and 1, 4-butanediol (BD). Effects of diols and comonomer molar ratio on the extent of polycondensation reaction and molecular weight of the resulting copolymers were investigated. Diacids and diol ratios of L-lactic acid (LLA), dimethyl terephthalate (DMT) and diol of 1/1/2, 1/2/4 and 2/1/2 were employed. Characterization of chemical structure, molecular weight and thermal and physical properties of the resulting copolymers were conducted by FTIR, NMR, and DSC.