Comparison of Gamma Radiation Crosslinking and Chemical Crosslinking on Properties of Methylcellulose Hydrogel

In this research, characteristics of methylcellulose (MC) films modified with two crosslinking methods were investigated. The first method was the use of a glutaraldehyde (GA) crosslinker to promote hemi-acetal linkages between MC chains. The second one was gamma irradiation to form insoluble MC gel by intermolecular crosslinking. The effects of the MC concentration on the degree of crosslinking, water absorption, gel content, degree of swelling, and thermomechanical properties were determined. The results indicate that the chemically crosslinked MC films show lower polarity than the radiation crosslinked films. The nature of the crosslinkings was also revealed with FTIR spectra. The water-swelled films of chemically crosslinked MC were found to provide homogeneous gel structure whereas the radiation crosslinked MC films were observed to render less uniform crosslinked films

Development of a Suture Pad for Medical Training from Silk Fiber Reinforced Polydimethylsiloxane Composite

The aim of this research is to develop a suture pad simulating human skin for suturing practice. The suture pad was fabricated with layers of artificial dermis and subcutis which reproduced the mechanical properties of skin. The main focus of this study was to reinforce polydimethylsiloxane with silk fiber to create a realistic dermis. The effects of silk fiber amount and aspect ratio on the mechanical properties of the suture pads were investigated. Results revealed that the tensile strength and modulus of the composite increased in relation to fiber content and aspect ratio. Composites with silk fiber exhibited higher tear resistance to suture thread compared with pure polydimethylsiloxane. Furthermore, the hardness of the composites was improved with the addition of silk fiber. It was found that polydimethylsiloxane composite reinforced with 2 phr of silk fiber with an aspect ratio of 1000 showed a hardness value similar to that of human skin. These results indicate that silk fiber reinforced polydimethylsiloxane composites can realistically simulate human skin and have the potential to be used as suture pads for medical training

KevlarTM Fiber-Reinforced Polybenzoxazine Alloys for Ballistic Impact Application

A light weight ballistic composites from KevlarTM-reinforcing fiber having polybenzoxazine (BA)/urethane prepolymer (PU) alloys as a matrix were investigated in this work. The effect of alloy compositions on the ballistic composite properties was determined. The results revealed that the enhancement in the glass transition temperature (Tg) of the KevlarTM-reinforced BA/PU composites compared to that of the KevlarTM-reinforced polybenzoxazine composite was observed. The increase of the elastomeric PU content in the BA/PU alloy resulted in samples with tougher characteristics. The storage modulus of the KevlarTM-reinforced BA/PU composites increased with increasing the mass fraction of polybenzoxazine. A ballistic impact test was also performed on the KevlarTM-reinforced BA/PU composites using a 9 mm handgun. It was found that the optimal contents of PU in the BA/PU alloys should be approximately 20wt%. The extent of the delaminated area and interfacial fracture were observed to change with the varied compositions of the matrix alloys. The appropriate thickness of KevlarTM-reinforced 80/20 BA/PU composite panel was 30 plies and 50 plies to resist the penetration from the ballistic impact equivalent to levels II-A and III-A of NIJ standard. The arrangement of composite panels with the higher stiffness panel at the front side also showed the best efficiency of ballistic penetration resistance

Characterizations of Poly(vinyl chloride)/Acrylonitrile Styrene Acrylate Blends for Outdoor Applications

Significant enhancement on impact property of poly(vinyl chloride)/acrylonitrile styrene acrylate (PVC/ASA) blends was observed. The effect of ASA content on mechanical characteristics, including impact strength, themomechanical properties, water absorption, and outdoor weathering durability were investigated. The results suggested that the impact strength of the PVC/ASA blends increased drastically at the ASA content of about 30 - 40 wt% and at the ASA content of 50 wt%, the significant high impact strength of up to 77.6 kJ/m2 was obtained. The modulus and strength under tensile and flexural loads of PVC/ASA blends were found to increase with the PVC fraction while glass transition temperature and heat deflection temperature systematically increased with increasing ASA content. The blends are partially miscible in nature as evidenced from the shift of the two glass transition temperatures towards each other in the dynamic mechanical analysis. In addition, ASA fraction in the blends provides improved resistance to UV radiation for the PVC/ASA blend sample under natural weathering. The obtained PVC/ASA blends clearly showed a potential use as high impact plastic products for outdoor application

Highly filled graphite/graphene/carbon nanotube in polybenzoxazine composites for bipolar plate in PEMFC

This research aims to develop polybenzoxazine (PBA) based composites suitable for bipolar plates in proton exchange membrane fuel cells (PEMFCs). PBA composites filled with carbon derivatives i.e. graphite, graphene, and multiwall carbon nanotubes (CNTs) were prepared. The effects of CNT contents from 0-2wt% at an expense of graphite with constant content of graphene and benzoxazine on properties of the obtained composites were investigated. It was found that the composite with 2wt% of CNTs exhibited through-plane thermal conductivity as high as 21.3 W/mK which is 44 times higher than that of the composite without CNTs. Also, this composite showed electrical conductivity of 364 S/cm, Flexural Strength of 41.5 MPa and Modulus 49.7 GPa, respectively. These values meet the requirements suggested by the Department of Energy, USA and confirm that these composites are great candidates as bipolar plates for PEMFC

Impact Response of Aramid Fabric-Reinforced Polybenzoxazine/Urethane Composites Containing Multiwalled Carbon Nanotubes Used as Support Panel in Hard Armor

The aim of this research project is to analyze support panels that are based on aramid fabrics which are reinforced with polybenzoxazine/urethane (poly(BA-a/PU)) composites and contain multiwalled carbon nanotubes (MWCNTs). Through the measurement of mechanical properties and a series of ballistic-impact tests that used 7.62 x 51 mm(2) projectiles (National Institute of Justice (NIJ), level III), the incorporated MWCNTs were found to enhance the energy-absorption (E-Abs) property of the composites, improve ballistic performance, and reduce damage. The perforation process and the ballistic limit (V-50) of the composite were also studied via numerical simulation, and the calculated damage patterns were correlated with the experimental results. The result indicated hard armor based on polybenzoxazine nanocomposites could completely protect the perforation of a 7.62 x 51 mm(2) projectile at impact velocity range of 847 +/- 9.1 m/s. The results revealed the potential for using the poly(BA-a/PU) nanocomposites as energy-absorption panels for hard armor

Mechanical properties and curing kinetics of bio-based benzoxazine–epoxy copolymer for dental fiber post

Abstract Biocopolymers based on vanillin/fufurylamine–biobenzoxazine (V-fa) and epoxide castor oil (ECO), a bioepoxy, were prepared for application as dental fiber-reinforced composite post. The mechanical and thermal properties of the V-fa/ECO biocopolymers were assessed with regard to the influence of ECO content. The addition of the ECO at an amount of 20% by weight into the poly(V-fa) preserved the stiffness, glass transition temperature and thermal stability nearly to the poly(V-fa). Differential scanning calorimetry (DSC) was used to examine the curing kinetics of the V-fa/ECO monomer system with different heating rates. To determine the activation energy (E a ), the experimental data were subjected to the isoconversional methods, namely Flynn–Wall–Ozawa (FWO) and Friedman (FR). The V-fa/ECO monomer mixture showed average E a values of 105 kJ/mol and 94 kJ/mol. The results derived using the curing reaction model and the experimental data were in good agreement, demonstrating the efficacy of the FWO method for determining the curing kinetics parameters. The simulated mechanical response to external applied loads by finite-element analysis of the tooth model restored with glass fiber-reinforced V-fa/ECO biocopolymer post showed a similar stress field to the tooth model restored with a commercial glass fiber post. Therefore, based on the findings in this work, it is evident that the bio-based benzoxazine/epoxy copolymer possesses a great potential to be used for dental fiber post. Graphical Abstrac

Effects of Alkyl-Substituted Polybenzoxazines on Tribological Properties of Non-Asbestos Composite Friction Materials

A series of substituted polybenzoxazines was synthesized and studied as binders in non-asbestos friction composite materials. The structures of the polybenzoxazines were varied in a systemic fashion by increasing the number and position of pendant alkyl (methyl) groups and was accomplished using the respective aromatic amines during the polymer synthesis step. By investigating the key thermomechanical and tribological characteristics displayed by the composite materials, the underlying structure-properties relationships were deconvoluted. Composite friction materials with higher thermomechanical and wear resistance properties were obtained from polybenzoxazines with relatively high crosslink densities. In contrast, polybenzoxazines with relatively low crosslink densities afforded composite friction materials with an improved coefficient of friction values and specific wear rates

Ultrafine fully vulcanized natural rubber modified by graft‑copolymerization with styrene and acrylonitrile monomers

This research aims to modify ultrafne fully vulcanized powdered natural rubber (UFPNR) prepared by emulsion graft-copolymerization with styrene (St) and acrylonitrile (AN) monomers onto deproteinized natural rubber (DPNR). The efects of monomers content and St/AN weight ratio on grafting efciency and thermal stability of the devel�oped DPNR-g-(PS-co-PAN) were investigated. The results showed that grafting efciency was enhanced up to 86% with monomers content 15 phr and weight ratio St:AN 80:20. The obtained DPNR-g-(PS-co-PAN) was radiated by an electron beam at various doses, followed by a spray drying process to produce UFPNR. The obtained modifed UFPNR particles irradiated at dose up to 300 kGy were relatively spherical with a particle size of approximately 4.4 µm. Fur�thermore, the degradation temperature of 5wt% loss (Td5) of UFPNR was found in the range of 349–356 °C. The results revealed that the modifed UFPNR is suitable as a toughening fller for a broader spectrum of polymers

Radiation graft-copolymerization of ultrafine fully vulcanized powdered natural rubber: Effects of styrene and acrylonitrile contents on thermal stability

Graft copolymers, deproteinized natural rubber-graft-polystyrene (DPNR-g-PS) and deproteinized natural rubber-graft-polyacrylonitrile (DPNR-g-PAN), were prepared by grafting of styrene (St) or acrylonitrile (AN) monomers onto DPNR latex via emulsion copolymerization. Then, ultrafine fully vulcanized powdered natural rubbers (UFPNRs) were produced by electron beam irradiation of the graft copolymers in the presence of di-trimethylolpropane tetraacrylate (DTMPTA) as crosslinking agent and subsequently a fast spray drying process. The effects of St or AN monomer contents and the radiation doses on the chemical structure, thermal stability, and physical properties of the graft copolymers and UFPNRs were investigated. The results showed that solvent resistance and grafting efficiency of DPNR-g-PS and DPNR-g-PAN were enhanced with increasing monomer content. SEM morphology of the UFPNRs showed separated and much less agglomerated particles with an average size about 6 μm. Therefore, it is possible that the developed UFPNRs grafted copolymers with good solvent resistance and rather high thermal stability can be used easily as toughening modifiers for polymers and their composites