Carbon-Carbon Composite Materials Based on Low Modulus Fabrics

Scientific research and the search for new technologies to increase the level of mechanical and high-temperature properties are ongoing. The article discusses the technology of using carbon materials, pyrolysis and impregnation with phenol-formaldehyde resins. It is shown that the proposed technology makes it possible to achieve a sufficient level of mechanical properties when using low-modulus carbon fabrics after pyrolytic treatment as a prepreg at a temperature treatment no higher than 900 K. Pillowcase and resole phenol-formaldehyde resins were used to impregnate the prepreg. The proposed technology also allows the introduction of alloying additives into the system to improve the properties. An example of the introduction of nitrogen into a composite by adding urotropine to a phenol-formaldehyde resin, which was used to impregnate the composite, is considered.

Fatty-acid-derived ester-urethane macromonomers synthesized using bismuth and zinc catalysts

Photocurable materials that can be delivered as liquids and rapidly (within seconds) cured in situ using UV light are gaining increased interest in advanced minimally invasive procedures. The aim of this work was to synthesize and characterize fatty-acid-derived ester-urethane telechelic (methacrylate) macromonomers, suitable for photopolymerization. The commonly used dibutyltin dilaurate catalyst was replaced with bismuth neodecanoate, bismuth tris(2-ethylhexanoate), and zinc (II) acetyloacetonate as less-toxic alternative catalysts. Additionally, ethyl acetate was used as a “green” solvent. The progress of the two-step synthesis was monitored with infrared spectroscopy. The chemical structure and molecular weight of the obtained viscous materials was characterized with nuclear magnetic resonance spectroscopy and gel permeation chromatography. Photocrosslinking of the macromonomers into elastomeric films was achieved using 150 s per spot of UV light (20 mW/cm2) exposure. Mechanical tensile testing of the films indicated their elasticity up to 120% and low modulus typical for soft and elastomeric materials. Finally, in vitro cytotoxicity tests showed high cell viability for the case of materials synthesized using bismuth and zinc catalysts. Overall, our results indicate that bismuth and zinc catalysts are excellent alternatives to organotin compounds in the synthesis of photocurable methacrylate ester-urethanes for potential biomedical applications.

Hybrid Carbon/Glass Fiber Reinforced Polymer; A Frontier Material for Aerospace Industry : A Review on Mechanical Properties Enhancement

Composite is the combination of two or more materials that differ in properties and composition to form unique properties. This paper reported in the literature on the field of deformation of hybrid composite under tensile, shear and flexural loading are presented in this chapter. This article review provides insight and state of the art for mechanics of composites that provides underlying theory for understanding the deformation and behaviour for the hybrid composite under various loading conditions. This paper also discusses mechanical behaviour of hybrid composites under static loading (Tensile, Shear, Flexural). It is essential to understand the principle that governs the mechanics of composites of laminate under loading which also applicable to hybrid composites C/GFRP.The high modulus fibre, such as Carbon fibre offers stiffness and load bearing capabilities, whereas the low modulus fibre, such as glass fibre makes the composite more durable and low in cost

Birefringent elastomers with Multiple Stimuli-Responses

Currently, even though birefringent soft materials have attracted considerable attention for many sensors and optical devices, it is still difficult for most of them to achieve multiple responses. Herein, we have designed a multiple-responding birefringent elastomer with high birefringence but low modulus by using 2-phenoxy-ethanoacrylate (PHEA) as monomer and 4-cyano-4'pentylbiphenyl as solvent. The excellent transparency (~90%) exhibited by the designed birefringent elastomer allowed us to observe the change of interference color. The obtained birefringent elastomer not only can be used as a photoelastic strain sensor with high sensitivity and fast response but also show a very sensitive response to heat, particularly in the range of the human body temperature. More interestingly, it shows excellent dielectric properties with a strong correlation between the interference color and the applied electric field, which allows easily writing and erasing the encrypted information. These unique multi-signal response features of our obtained birefringent elastomer shed light on the multiple information encryptions, the anti-counterfeiting, and the multifunctional sensors.

Endodontically Treated Maxillary Premolars Restored with Glass Fiber Post under All Ceramic Crown

Glass fiber posts and core are increasingly used in order to restore severely damaged endodontically treated teeth and particularly maxillary premolars that are prone to fracture. Their low modulus of elasticity which is similar to that of dentin allows the post to absorb stress and prevent root fracture. In addition, the glass fiber posts provide a natural hue by integrally bonding to the composite, thereby improving the aesthetics without compromising much on the strength. Various factors are involved in the longevity of such treatment option, remaining tooth structure seems to be the most important. Key words: glass fiber posts, premolars, endodontically treated teeth, composite resin, fracture resistance, crown, ferrule, failure .

Influence of Flax Fibre Hybridization on Mechanical Behaviour of Sisal Fibre-Polypropylene Composites Prepared with an Injection Moulding Machine

Due to their low weight, high specific strength, and low environmental impact, sisal fibre-polypropylene composites have gained popularity. However, the material has a low modulus and poor moisture resistance, among other shortcomings. This study investigated how flax fibre hybridization affects the physical parameters of sisal fibre-polypropylene composites. We used maleic anhydride-grafted polypropylene to improve compatibility between fibres and polypropylene. Adding flax fibres to polypropylene-silica composites resulted in increased tensile strength, flexibility, and impact strength, according to researchers. Water resistance was further improved by adding flax fibres. Tensile strength values of polypropylene-sisal fibre composites filled with 0, 5, 10, 15, and 20 wt% of flax fibres were 29.46, 30.56, 31.57, 33.12, and 34.64 MPa, respectively.