Sarawut Rimdusit

High performance wood composites based on benzoxazine-epoxy alloys

Wood-substituted composites from matrices based on ternary mixtures of benzoxazine, epoxy, and phenolic novolac resins (BEP resins) using woodflour (Hevea brasiliensis) as filler are developed. The results reveal that the addition of epoxy resin into benzoxazine resin can lower the liquefying temperature of the ternary systems whereas rheological characterization of the gel points indicates an evident delay of the vitrification time as epoxy content increased. The gelation of the ternary mixtures shows an Arrhenius-typed behavior and the gel time can be well predicted by an Arrhenius equation with activation energy of 35-40kJ/mol. For wood-substituted composites from highly filled BEP alloys i.e. at 70% by weight of woodflour, the reinforcing effect of the woodflour shows a substantial enhancement in the composite stiffness i.e. 8.3GPa of the filled BEP811 vs 5.9GPa of the unfilled BEP811. The relatively high flexural strength of the BEP wood composites up to 70MPa can also be obtained. The outstanding compatibility between the woodflour and the ternary matrices attributed to the modulus and thermal stability enhancement of the wood composites particularly with an increase of the polybenzoxazine fraction in the BEP alloys.

Shape memory polymers from benzoxazine-modified epoxy

Novel shape memory polymers (SMPs) were prepared from benzoxazine-modified epoxy resin. Specimens consisting of aromatic epoxy (E), aliphatic epoxy (N), Jeffamine D230 (D) and BA-a benzoxazine monomer (B) were evaluated. The mole ratio of D/B was used as a mixed curing agent for an epoxy system with a fixed E/N. The effects of BA-a content on the thermal, mechanical and shape memory properties of epoxy-based shape memory polymers (SMPs) were investigated by differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), flexural test and shape recovery test. The results revealed that the obtained SMPs exhibited a higher flexural strength and flexural modulus than those of the unmodified epoxy-based SMP at room temperature and at 20?? C above glass transition temperature (Tg). The presence of 1?mol BA-a as a curing agent provided the specimen with the highest Tg, i.e. about 72?? C higher than that of epoxy-based SMP cured by Jeffamine D230. All SMP samples needed only a few minutes to fully recover to their original shape. The samples exhibited high shape fixity (98?99%) and shape recovery ratio (90?100%). In addition, the recovery stress values increased with increasing BA-a mole ratio from 20 to 38?kPa, when BA-a up to 1?mol ratio was added. All of the SMP samples exhibited only minimum change in their flexural strength at the end of a 100 recovery cycles test.

Characterization of SiC Whisker-Filled Polybenzoxazine Cured by Microwave Radiation and Heat

Abstract The effect of microwave and thermal curing on the properties of SiCw-filled polybenzoxazine is examined. The benzoxazine resin (BA-a) can be cured thermally above 150°C but was hardly cured by microwave irradiation even using a power up to 1 kW. The presence of only 4% by weight of the SiCw significantly reduces the processing time of the composites from two hours at 200°C using the traditional thermal cure to less than 20 minutes using a microwave cure power of 270 W. The mechanical and thermal behaviors of the SiCw-filled polybenzoxazine show no significant difference with either curing methods.

Characterization of coconut fiber-filled polyvinyl chloride/acrylonitrile styrene acrylate blends

Coconut fiber-filled composites based on PVC/ASA blend were developed. The results reveal that the impact strengths of the PVC/ASA/coconut fiber composites are significantly higher than those of PVC wood composites or polyolefin wood composites when comparison was made at the same fiber content. Dynamic mechanical analysis thermograms exhibit two distinct glass transition temperatures ( T g s ) of the blend matrix, indicating partial miscibility of the blends. The storage modulus at room temperature and T g s of the composites systematically increase with the fiber content. The tensile strength value of the blend as high as 45 MPa was obtained and found to only slightly decrease with the fiber content. The PVC/ASA blend shows a potential use as a matrix of high-impact wood composite products with good thermal dimension stability due to the outstanding impact strength and thermal properties of the blend.

Chapter 7 – Polymerization Kinetics

Publisher Summary The polymerization reaction kinetics of benzoxazine resins is described in this chapter. Polymerization, in polymer chemistry, is the process of reacting monomer molecules together in a chemical reaction to form three-dimensional networks or polymer chains. There are many forms of polymerization and different systems exist to categorize them. The chemistry of the polymerization begins by formation and linear growth of the chain that soon begins to branch and then to cross-link. As the reaction proceeds, the molecular weight increases rapidly and eventually several chains become linked together into networks of infinite molecular weight. The resulting polymer, if properly processed, is a highly cross-linked, three-dimensional infinite network. The nature of the polymerization reactions of a thermosetting polymer or the macroscopic kinetics is very complex in that many reactive processes sometimes occur simultaneously. In addition, reinforcements, fillers, pigments, and other additives are commonly added. Therefore, the understanding of polymerization kinetics contributes to both a better knowledge of process development and an improvement in the quality of the final products related to the structures of the polymer networks. This chapter summarizes the polymerization reaction of epoxy novolac resin by BA-a. The polymerization of a BA-a: EP mixture is characterized by two predominant reactions, as evidenced by the presence of a double peak in the DSC thermograms. The activation energy value of reaction is similar to the activation energy for polymerization of the neat BA-a, supporting reaction as the reaction among the benzoxazine monomers.

Surface Segregation-typed Polyimide Blends between Silicon-containing Polyimide and Polyimides of Varied Chain Flexibility

Surface segregation behaviors of blending systems between polysiloxane‐block‐polyimide (SPI) and three polyimides with different chain flexibility (PMDA/ODA, s‐BPDA/ODA, and ODPA/ODA) have been investigated. All film samples with 50 μm thickness were characterized by surface profilometer, attenuated total reflection infrared (ATR‐IR), and ATR microscope. In this study, the films with various PSI contents were processed on a glass substrate. At low concentration of PSI (less than 10 phr), three types of the polyimides trended to migrate to the glass‐side surface, while PSI component trended to migrate to the air‐side surface. For high concentration of PSI (i.e., 10 phr and 30 phr), the glass‐side surface was covered with the polyimides, whereas the air‐side surface showed two different colors. ATR microscope revealed PMDA/ODA blending system exhibited the highest segregation level.

Organic Based Heat Stabilizers for PVC: A Safer and more Environmentally Friendly Alternatives

Organic based stabilizers have been considered as a new technology providing environmentally friendly heat stabilizer for PVC pipe production to substitute conventional lead stabilizer as well as calcium zinc stabilizer. In this research, PVC samples stabilized with 5 types of heat stabilizers i.e. 1) commercial lead stabilizer, 2) commercial calcium zinc stabilizer, 3) commercial organic based stabilizer (OBS), 4) 1,3-dimetyl-6-aminouracil (DAU) and 5) eugenol, were investigated. From dynamic mechanical analysis, storage modulus at room temperature of PVC stabilized with DAU was found to provide the highest value among those stabilizers. Glass transition temperature of the PVC stabilized with all types of heat stabilizers was determined to be approximately 99°C except the value of about 89°C in eugenol stabilized PVC. Furthermore, PVC stabilized with commercial lead, calcium zinc stabilizer and commercial OBS could be reprocessed up to at least 5 cycles. Whereas, PVC stabilized with DAU was found to be able to withstand the processing cycle up to 4 cycles. Additionally, PVC stabilized with DAU showed the most outstanding short term thermal stability and can maintain its original color for at least up to 4 processing cycles. Finally, repeated processing of PVC stabilized with each type of heat stabilizers showed negligible effect on mechanical properties for at least up to 3 processing cycles. From the above results, it is evident that DAU showed high potential use as a safe and effective organic based heat stabilizer for PVC to substitute traditional lead or calcium zinc compounds.

Chemorheology of Benzoxazine-based Resins

Publisher Summary This chapter discusses the chemorheology of benzoxazine-based resins. Processing windows of benzoxazine resins are observed to vary among different types of benzoxazines and their modification by other resins. Chemorheology or the study of the viscoelastic properties of reacting systems encompasses an investigation of the variations in viscosity due to chemical reactions and processing conditions as well as characterization of the growth of the infinite molecular network (gelation) and the immobilized glassy state (vitrification). The variation in viscosity of resin due to changes in temperature or time is regarded as the processing window of the resin. In the processing window, the viscosity of the resin may initially decrease due to heating past its liquefying or softening point to reach its minimum value. At the point of minimum viscosity, the resin can conveniently be processed or transferred into the mold. The viscosity of the resin increases through the curing process past its gel point and the material is transformed into an infusible solid. Liquid-type modifiers are found to lower the devitrification points of benzoxazine resins and can be easily investigated by rheological technique. This chapter explores the two main events that occur during the cross-linking process of thermosetting resin, which are gelation (a liquid-to-rubber transition) and vitrification (a liquid- or rubber-to-glass transition). It describes Gel that is defined as a soft solid or solid-like material, which consists of two or more components, one of them being a liquid present in substantial quantity. Therefore, it will show a flat mechanical spectrum in an oscillatory shear experiment.

Thermal and Mechanical Properties of Acrylonitrile-Butadiene Rubber Modified Polybenzoxazine as Frictional Materials

Frictional composites based on polybenzoxazine (PBA-a) and acrylonitrile-butadiene rubber (NBR) are developed in this study. Mechanical, thermal and tribological properties of the PBA-a/NBR composites at 0, 2, 5, 10 and 15wt% of NBR particle contents are evaluated. Curing behaviors of the NBR-benzoxazine molding compounds are examined by differential scanning calorimetry to show an exothermic peak of about 222°C compared with that of the benzoxazine resin, i.e. 232°C suggesting curing acceleration of the benzoxazine resin due to the presence of the NBR particles. The storage modulus of the NBR-filled PBA-a is observed to systematically decrease from 5.2 GPa of the neat PBA-a to 2.8 GPa with an addition of 15wt% of the rubber particles. Glass transition temperature (Tg) of the composites evaluated by dynamic mechanical analysis increases with increasing of NBR particle contents, i.e. from 172°C for PBA-a to 186°C for PBA-a/15wt% NBR. Furthermore, the friction coefficients of the composites with 2wt% NBR are determined to be 0.603 for static type and 0.528 for kinetic type. Those values are improved from the value of 0.597 and 0.475 for unmodified polybenzoxazine, respectively. Therefore, the obtained outstanding properties, i.e. storage modulus, glass transition temperature and friction coefficient make the polybenzoxazine composites highly attractive to be utilized as friction materials.

Investigation on Rubber-Modified Polybenzoxazine Composites for Lubricating Material Applications

Effects of liquid amine-terminated butadiene-acrylonitrile (ATBN) on the properties of bisphenol-A/aniline-based polybenzoxazine (PBA-a) composites were investigated. Liquid ATBN decreased gel time and lowered curing temperature of the benzoxazine resin (BA-a). The PBA-a/ATBN-based self-lubricating composites resulted in substantial enhancement regarding their tribological, mechanical, and thermal properties. The inclusion of the ATBN at 5% by weight was found decreasing the friction coefficient and improved wear resistance of the PBA-a/ATBN composites. Flexural modulus and glass transition temperature of the PBA-a composite samples added the ATBN was constant within the range of 1-5% by weight. A plausible wear mechanism of the composites is proposed based on their worn surface morphologies. Based on the findings in this work, it seems that the obtained PBA-a/ATBN self-lubricating composites would have high potential to be used for bearing materials where low friction coefficient, high wear resistance, and modulus with good thermal property are required.