Chanchira Jubsilp

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.

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.

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.

Effect of Rubber Contents on Tribological and Thermomechanical Properties of Polybenzoxazine

Bisphenol-A/aniline based polybenzoxazine (PBZ) modified with amine terminated butadiene–acrylonitrile (ATBN) were prepared. The tribological and thermomechanical properties as well as thermal stability of the PBZ/ATBN copolymers were investigated by ball-on-disc tribometer, dynamic mechanical analysis (DMA), universal test machine and thermogravimetric analysis (TGA). The inclusion of ATBN at a mass fraction of 5% was found to greatly increase friction coefficient and wear resistance of the copolymers. DMA measurements showed that the storage modulus and the glass transition temperature of the PBZ can be maintained with an addition of ATBN in the range of 1-5wt%. Moreover, flexural property measurements indicated that the flexural strength of the copolymer increased with increasing of ATBN content up to 10wt% whereas TGA results revealed that an increase of the PBZ content can help improve thermal stability of the copolymers.

Introduction to Commercial Benzoxazine and Their Unique Properties

Since World War II, only few polymers, which have been developed, are able to reach the commercial stage. Polybenzoxazines are one of those few. Their ease of synthesis with tremendous molecular design flexibility allows tailor-made properties with broad range of applications. Their unique characteristics such as self-polymerizability upon heating without a need for a catalyst or curing agent, very low A-stage viscosity, near-zero volumetric shrinkage, fire-resistant behaviors, as well as their outstanding thermal and mechanical properties, make the polymer highly attractive for various applications including electronic packaging or aerospace. As a consequence, some companies start to commercialize the resins and their composites. This chapter summarizes benzoxazine resins and their related products recently commercialized by some major companies. The key properties of the polymers for engineering applications are also concisely discussed.

Natural rubber latex-modified asphalts for pavement application: effects of phosphoric acid and sulphur addition

This research aims to investigate physical, storage stability, morphology and rheological properties of asphalt modified by natural rubber (NR), polyphosphoric acid and sulphur. NR is used in a latex form to avoid a severe mixing condition. A small quantity of PPA and sulphur are proved to be effective modifiers in addition to NR. It is found that when asphalt is modified with 0.6–4.5 wt% of NR, 1–2 wt% of PPA and 0.3–1.0 wt% sulphur (based on 100 parts of NR), penetration of the modified asphalt systematically decreases while its softening points and Brookfield viscosity increase with increasing NR and PPA contents. An addition of sulphur in the asphalt system shows complementary improvement in its toughness and tenacity. Our results suggest the modified asphalt with 3.2 wt% of NR, 2 wt% of PPA and 0.3 wt% of sulphur is a suitable formula for the road condition in Thailand.

Newly High-Performance Wood-Substituted Composites Based on Polybenzoxazines

Wood-substituted composites of natural woodflour-filled polybenzoxazine and theirs polybenzoxazine alloys with high mechanical properties, good thermal stability, and reduced water uptake have been developed. The outstanding compatibility between the woodflour and the polybenzoxazine-based polymer matrix is evidently seen from the large improvement in the composite’s mechanical properties, glass-transition temperature (T g ), and char yield as also evidently seen in the fracture surface of the wood polymer composites based on polybenzoxazine. At the optimal woodflour content of 70 % by weight in polybenzoxazine results in the composite’s T g as high as 200 °C or about 40 °C greater than that of the neat polybenzoxazine and the modulus in a range of 6.4–6.8 GPa compared to that of natural Hevea brasiliensis wood, i.e., 9.7 GPa. Polybenzoxazine is thus proved to be useful as an effective binder for lignocellulosic materials such as woodflour.

Polybenzoxazine Composites for Ballistic Impact Applications

This chapter discusses the utilization of polybenzoxazine/urethane alloys with fine-tuning properties for ballistic impact composite application. The ballistic impact study of KevlarTM fiber-reinforced polybenzoxazine alloys under the test weapon with standard 124 grains round lead projectile and a copper outer coating (Full Metal Jacket) typically used in the 9-mm handgun at an impact velocity of 426–431 m/s is reported. The polybenzoxazine/urethane alloy matrices at various urethane prepolymer contents were prepared to evaluate the effect of different urethane contents on the thermal, mechanical as well as ballistic resistant properties. Experimental results reveal a synergy in glass transition temperature and some mechanical properties of the alloys at the composition range of 10–30 % by weight of urethane fraction the thus provide a fascinating group of high temperature polymers with improved flexibility and enhanced a ballistic resistant characteristic.