Pranee Phinyocheep

Green natural rubber-g-modified starch for controlling urea release

The hydrophilicity of natural rubber (NR) was improved by grafting with modified cassava starch (ST) (NR-g-ST) by using potassium persulfate (K2S2O8) as a catalyst. The modified ST was added to NR latex in the presence of Terric16A16 as a non-ionic surfactant at 60 °C for 3 h and cast film on a glass plate to obtain NR-g-ST. The chemical structure of NR-g-ST was confirmed by FTIR. The swelling ratio of NR-g-ST was investigated in water and results showed that the swelling ratio of the modified NR decreased as function of ST. In addition, the tensile strength of the modified NR in the presence of modified ST at 50 phr was the highest value. Also, the thermal stability modified NR-g-ST was higher than of NR/ST blend confirmed by TGA. Finally, the NR-g-ST was used a polymer membrane for controlling urea fertilizer and it easily degraded in soil. This product with good controlled-release and water-retention could be especially useful in agricultural and horticultural applications.

Ultraviolet-curable liquid natural rubber

Preparation of ultraviolet (UV)-curable liquid natural rubber was achieved by fixation of photosensitive molecule onto liquid natural rubber. The liquid natural rubber (LNR) was prepared by oxidative degradation of natural rubber latex, using the phenylhydrazine/O2 system. The LNR was further treated with in situ performic acid, which leads to epoxidized liquid natural rubber (ELNR). The progress of the addition reaction of photosensitive acrylic acid onto epoxide ring of the ELNR was followed by infrared spectroscopy. It was found that at 80°C reaction temperature, epoxide ring opening reaction of ELNR came to completion within 2 h, which is faster than the reaction at 60°C. The photocrosslinking reaction of the acrylated ELNR was studied by monitoring the exothermic heat of photocuring of acrylate double bond using a double beam photocalorimeter (DPA7). It was found that the fast crosslinking-polymerization occurred when the rubber was exposed to UV irradiation in the presence of photocleavage initiator (Irgacure 184 and Darocur 1173) and liquid diacrylate monomer (1,6 hexanediol diacrylate and tripropylene glycol diacrylate). The cure kinetics of the elastomers were also investigated, and it was found that the diacrylate monomer, photoinitiator concentration play an important role on the rate and extent of the reaction.

Atom transfer radical polymerizations of (meth)acrylic monomers and isoprene

Abstract Atom transfer radical polymerizations (ATRP) of methyl methacrylate (MMA), ethyl acrylate (EA), and isoprene through the use of CuBr/N,N,N′,N′,N′′-pentamethyl diethylenetriamine catalyst and ethyl bromoproprionate initiator were studied as a function of polymerization parameters. Chemical structure, percentage yield and molecular weight of products were analyzed by gravimetry, FTIR, 1 H-NMR and GPC techniques. Polymerized products having a considerable high percentage yield was obtained from the polymerization of MMA and EA. The percentage yield and molecular weight of PMMA increased with reaction temperature, reaction time, monomer concentration and initiator content. There was also an optimum catalyst content corresponding to the maximum yield and molecular weight of PMMA. The polymerization of EA also showed a similar trend. ATRP of isoprene, however, resulted in only a trace amount of product, irrespective of reaction parameters. The low product yield from the ATRP of isoprene was attributed to a poor solubility of CuBr and tris[2-(dimethylamino)ethyl]amine catalyst in isoprene and the limited reaction temperature.

Chemical treatment of wood for musical instruments. Part I: acoustically important properties of wood for the Ranad (Thai traditional xylophone)

The purpose of this study is to determine the important acoustic properties of wood for making Ranad bars and the resonator box. The woods used in this study were separated into two groups. The first group is the type of wood that has been used to make Ranad for centuries: Ching-Chan (Dalbergia oliveri Gamble) and Ma-Had (Artocarpus lakoocha Roxb.) for making the bars, and Ka-Nun (Artocarpus neterophylla Lamk.) out of which the resonator box is made. The second group comprises woods that are abundant in Thailand and are genetically related to the first group. The physical and mechanical properties of the woods in both groups were measured including the specific dynamic Young’s modulus (E/ρ), density (ρ), hardness (H), acoustic conversion efficiency (ACE), and sound refraction coefficients (|Γ|). The results revealed that high and consistent |Γ| were crucial factors of the Ranad bar properties in addition to E/ρ, ρ, and H. The results from measurements made on the resonator box wood revealed that high E/ρ, ACE, and high and consistent |Γ| were its crucial properties.

Lipase-catalyzed synthesis of hydrophobically modified dextrans: Activity and regioselectivity of lipase from Candida rugosa

Vinyl decanoate-modified dextran macromolecules (DexT40-VD) were synthesized in dimethyl sulfoxide at 50°C using lipase AY from Candida rugosa for catalyzing transesterification between polysaccharide and vinyl fatty esters. The extent of dextran modification (quantified by the molar ratio of attached alkyl tails to sugar repeat units) with native-, pH-adjusted-, 18-crown-6 ether pretreated pH-adjusted-, and stepwise addition of pretreated lipase AY yielded <3%, 49%, 64% and 96% modified dextran respectively. Lipase AY accelerated the transesterification of DexT40 from 2- to 63-fold higher than the non-catalyzed system. This procedure was extended to other acyl donors showing that modification pattern exhibited regioselectivity depending on acyl donor structure. Regioselectivity equaled between 2- and 3-OH with saturated fatty acyl donors. The 2-OH was favored for unsaturated fatty acyl donors, while sterically hindered acyl donors oriented modification toward 3-OH position. DexT40-VD at 96% modification was a water-insoluble polymer forming 150nm diameter nanoparticles in water which can be used as drug carrier systems.

Water Vapor Permeability and Mechanical Properties of Biodegradable Chitosan/Methoxy Poly(ethylene glycol)-b-Poly(ε-caprolactone) Nanocomposite Films

Nanocomposite films of chitosan/methoxy poly(ethylene glycol)-b-poly(ϵ-caprolactone) diblock copolymer were prepared by film casting of a diblock copolymer nanoparticle suspension-chitosan solution. The results obtained from thermogravimetric analysis confirmed that intermolecular bonds existed between the chitosan and the diblock copolymer. Percent moisture uptake and water vapor permeability of the chitosan films were decreased by incorporating diblock copolymer nanoparticles and decreased with increasing diblock copolymer content. The studies on tensile properties have shown that incorporation of nanoparticles into the chitosan film enhanced the tensile strength of the films in both dry and hydrated states.

Intramolecular acylation of α-sulfinyl carbanion: A new general route to 5-substituted Δ2 cyclopentenones

Abstract A general method for the preparation of 5-substituted Δ2-cyclopentenones via the intramolecular acylation of αot -sulfinyl carbanions has been demonstrated.

Reinforcing biofiller “Lignin” for high performance green natural rubber nanocomposites

High performance eco-friendly natural rubber biocomposites filled with 5, 10, 20, and 40 parts per one hundred rubber by weight (phr) of lignin were prepared from sodium lignosulfonate and natural rubber (NR) latex using the soft processing method. The formation of network-like lignin structures was detected around the rubber phases even when the amount of lignin was increased to 40 phr. The Payne effect clearly suggested the presence of filler–filler interaction of lignin in the biocomposites. The distinguishably superior reinforcement effects of lignin at different levels of content were clearly apparent in the biocomposites. Specifically, the tensile stresses of the biocomposites significantly increased with an increase in the lignin content. Under dynamic conditions, the biocomposites showed larger storage moduli and lower dissipative loss with low glass transition temperatures with increasing amount of lignin. The generation of crystallites by strain-induced crystallization (SIC) was evaluated by using quick time-resolved wide-angle X-ray diffraction/tensile measurements, and a stepwise SIC phenomenon was observed for the lignin-filled NR soft biocomposites. This is a first report on the organic filler filled NR nanocomposite. The lignin content did not significantly affect the generation of crystallites of the NR biocomposites. This characteristic could strongly influence the development of rubber science and technology. Sodium lignosulfonate will be applicable as a good reinforcing biofiller for the preparation of green NR nanocomposites.

Spectroscopic Investigation of Polystyrene Surface Grafting on Natural Rubber

This paper investigates the structural characteristics of polystyrene (PS) grafted on a natural rubber (NR) surface using Raman scattering spectroscopy. The nitroxide-mediated radical polymerization (NMRP) technique was used to achieve the graft copolymerization of PS onto the surface of NR film using 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) as a nitroxide mediator. The reversible reaction between propagating radical and TEMPO of the NMRP process leads to a controlled radical polymerization of styrene on the NR surface. The grafting degree of PS on the NR was first measured by gravimetric methods. It was found to depend linearly on the grafting time. The characteristic signals detected by Raman scattering and by attenuated total reflection (ATR) Fourier transform infrared (FT-IR) spectroscopy provide clear evidence of the PS being grafted onto the NR. The distribution of the grafted PS on the NR substrate was determined from the Raman mapping. It is seen that the grafting occurs homogeneously over the entire surface (∼40 mole % PS). The study using the Raman depth profiling technique on the original sample compared with the analysis carried out on the sample prepared by cross-sectioning led to important and comparable information regarding the uniform distribution of PS grafting inside the substrate.

Synthesis of acrylated styrene-isoprene-styrene copolymer

Abstract Vulcanization of polymer by ultraviolet irradiation has been playing an important role in the industrial sector especially for coating, ink and printing applications. Polymers used in this area are sensitive to ultraviolet (UV) radiation. Their final products have properties required for particular specifications. One of the methods to synthesize ultraviolet-sensitive polymers is the grafting of ultraviolet-sensitive units onto other polymer backbones. In this work, styreneisoprene- styrene copolymer (SIS) was selected as a polymer backbone whilst acrylic acid served as an ultraviolet sensitiser. The grafting reaction was carried out in a solution state of toluene through the ring-opening addition reaction of epoxidized SIS molecules. The results indicated that acrylic acid can be successfully grafted onto a previously epoxidized SIS backbone at a reaction temperature of 100°C. Furthermore, the acrylation yield increased with the increase of reaction time.