Sirilux Poompradub

Strain-induced molecular orientation and crystallization in natural and synthetic rubbers under uniaxial deformation by in-situ synchrotron X-ray study

Abstract In-situ synchrotron wide-angle X-ray diffraction (WAXD) studies and simultaneous measurements of stress and strain during uniaxial stretching of various vulcanized rubbers were carried out (at room temperature and 0°C) to reveal the strain-induced molecular orientation and crystallization relationships. Rubbers evaluated included natural rubber (NR), synthetic poly-isoprene rubber (IR), poly-cis-1,4-butadiene rubber (BR) and butyl rubber (IIR). Some universal features were observed in these systems: (i) At high strains (> 5.0), the majority of the chains (up to 50 ≈ 75%) in natural and synthetic rubbers remained in the un-oriented amorphous state with only a small amount of crystalline fraction formed (10–20%). The rest of the chains were in the oriented amorphous state. (ii) During deformation, the oriented amorphous chains acted as precursors to strain-induced crystallization. A network of micro-fibrillar crystallites is formed within the closely populated vulcanization points, leading to the e...

Increasing the Thermal Storage Capacity of a Phase Change Material by Encapsulation: Preparation and Application in Natural Rubber

Existing encapsulated organic phase change materials (PCM) usually contain a shell material that possesses a poor heat storage capacity and so results in a lowered latent heat storage density of the encapsulated PCM compared to unencapsulated PCM. Here, we demonstrate the use of a novel microencapsulation process to encapsulate n-eicosane (C20) into a 2:1 (w/w) ratio blend of ethyl cellulose (EC):methyl cellulose (MC) to give C20-loaded EC/MC microspheres with an increased heat storage capacity compared to the unencapsulated C20. Up to a 29 and 24% increase in the absolute enthalpy value during crystallization and melting were observed for the encap-C20/EC/MC microparticles with a 9% (w/w) EC/MC polymer content. The mechanism that leads to the increased latent heat storage capacity is discussed. The blending of the water-dispersible C20-loaded EC/MC microspheres into natural rubber latex showed excellent compatibility, and the obtained rubber composite showed not only an obvious thermoregulation property but also an improved mechanical property.

Thermal and mechanical properties of poly(lactic acid)/natural rubber blend using epoxidized natural rubber and poly(methyl methacrylate) as co-compatibilizers

AbstractIn order to improve the toughness of poly(lactic acid) (PLA), the incorporation of natural rubber (NR), which has a high elasticity and flexibility, can be used. However, the phase incompatibility between PLA and NR can cause poor mechanical properties of the final product in the absence of a compatibilizer because of their different polarities. In this research, epoxidized NR (ENR) and poly(methyl methacrylate) (PMMA) were used as co-compatibilizers for linking PLA/NR blends (PLA 100: NR 15 parts by weight per hundred parts of resin (phr)). Therefore, the aim of this research was to study the effect of the ENR/PMMA co-compatibilizer contents on the mechanical, thermal and morphological properties of the 100:15 phr PLA/NR blend. With 3 phr of ENR and 1 phr of PMMA, the elongation at break and impact strength of the 100:15 phr PLA/NR blend was significantly improved up to 1,813% and 362%, respectively. The thermal stability of the PLA/NR blend was also increased when using the co-compatibilizers. Interestingly, the PLA/NR blend containing the co-compatibilizer showed a high ultimate tensile strength after thermal aging at 100 °C for 1 h with good mechanical properties. However, the percentage of crystallinity and glass transition temperature were decreased by the added co-compatibilizer. Finally, a good compatibility between the PLA and NR matrices could be clearly observed by scanning electron microscopy in the presence of the co-compatibilizer.

In Situ Silica Filled Styrene Grafted Natural Rubber by the Sol-Gel Process

In situ silica filling of styrene grafted natural rubber (ST-g-NR) was carried out by using sol-gel reaction of tetraethoxysilane (TEOS). The effects of concentration of catalyst and reaction temperature on the in situ silica content were investigated. ST-g-NR was synthesized via an emulsion polymerization using cumene hydroperoxide (CHPO) and tetraethylene pentamine (TEPA) as initiators. The synthesized ST-g-NR was characterized by a Fourier Transform Infrared Spectroscopy (FTIR) and Proton Nuclear Magnetic Resonance Spectroscopy (1H NMR). The content of in situ silica generated in ST-g-NR matrix was determined by Thermogravimetry Analysis (TGA). In situ silica up to 50 parts per hundred rubbers by weight (phr) was successfully filled in the ST-g-NR matrix. The silica content increased with the increase of n-hexylamine concentration. However, the effect of reaction temperature was insignificant to silica content.

Smart Green Composite: Effect of Cuttlebone Particle on the Mechanical Properties of NR Vulcanizates

The purpose of this study was to investigate the reinforcement effect of the cuttlebone particle on the mechanical properties of natural rubber (NR) vulcanizates. The extraction of organic compound from the cuttlebone was prepared demineralization and deproteinization methods. The obtained chitin had been characterized by Fourier Transform Infrared Spectroscopy (FTIR). The mechanical and thermal properties of NR composite materials were investigated. The reinforcement effect of cuttlebone particle in NR composite was comparable with that of commercial CaCO3 as a reference. After thermal aging, the tensile properties of composite material were decreased. The presence of organic component was speculated to give a good interaction effect of cuttlebone particles to NR as revealed by Scanning Electron Microscopy (SEM).

Preparation of antibacterial composite material of natural rubber particles coated with silica and titania

Silica coating, followed by titania coating, was performed over spray-dried natural rubber (NR) compound for physical and anti-bacterial characterizations. Titania has a strong photo-oxidative catalytic property, which can disinfect bacteria, but may degrade NR. Therefore, silica coating was intended to form a barrier between NR and titania. First, NR particles were prepared by spray-drying of NR compound latex, formulated for household glove products, mixed with sodium dodecyl sulfate (SDS) to reduce particle agglomeration. The factorial experimental design was employed to investigate the effects of nozzle flow rate (500-700 Lh-1), inlet air temperature (110-150 °C), SDS content (35-55 phr) and mass flow rate (1.2-1.7 g rubber/min) on NR yield and moisture content. Then, the NR compound particles prepared at the optimum condition were coated with silica, using tetraethoxysilane (TEOS) as the precursor, by chemical vapor deposition (CVD) at 60 °C for 2-48 hours. Next, the particles were coated with titania using titanium tetrafluoride (TiF4) by liquid phase deposition (LPD) at 60 ºC for 4-8 hours. The NR composites were characterized for surface morphology by SEM, silica and titania content by TGA and EDX. The NR composites were found to cause more than 99% reduction of Escherichia coli and Staphylococcus aureus under 1-hour exposure to natural light.

Preparation of sulfonic acid-containing rubbers from natural rubber vulcanizates

In this work, a series of sulfonic acid-containing rubbers were prepared by aqueous phase oxidation of natural rubber vulcanizates in the presence of hydrogen peroxide (H2O2) and formic acid (HCOOH). The starting vulcanizates were neatly prepared via an efficient vulcanization (EV) system by varying mass ratio of N-cyclohexyl-2-benzothiazole sulfonamide (CBS), as an accelerator, to sulfur. The oxidation conditions were controlled at the molar ratio of H2O2: HCOOH = 1:1, the concentration of H2O2 = 15 wt.%, the temperature = 50 °C, and the reaction time = 3 h. The rubber materials before and after the oxidation were characterized for their physicochemical properties by using Fourier transform infrared spectroscopy, bomb calorimetry, acid-base titration and swelling measurements. The results indicated the presence of sulfonic acid group in the oxidized rubbers, generated by the oxidative cleaves of sulfide crosslinks in the rubber vulcanizates. The oxidation decreased the sulfur content of the rubber in which the level of sulfur loss was determined by the CBS/sulfur ratio. Moreover, the acidity of the oxidized products was correlated with the amount of sulfur remaining.