Key Engineering Materials Vol. 845

Abstract: Utilization of natural fibers in a form of filler materials in composite structures has been successfully implemented in a broad range of industrial applications. In general, natural fibers have many advantages over synthetic counterparts, (e.g. glass and carbon) including lower density, ability to muffling vibration as well as its positive environmental impact. Hence, natural fibers can be used to enhance the characteristics of composite polymers. Expected improvements may include good thermal and acoustic insulating properties and better electrical resistance. However, in order to qualify any new developed material for commercialization, machining such as drilling, milling, cutting, bending, etc., becomes essential. In this experimental work, a newly developed Chopped Date Palm Fronds Polypropylene (CDPF/PP) bio-composite, which was mechanically characterized in a previous study, is investigated against conventional drilling operation. The data obtained through machining are processed and statistically analyzed based on Design of Experiment (DoE) to achieve the optimal input parameters using ANOVA and regression model. Moreover, the statistical evaluation of the results is useful to develop mathematical models that can be used with confidence to predict the drilling delamination for future works. In specific, optical microscopy was utilized to measure the dimension of the machined bio-composite surface to calculate the delamination factor.

Abstract: Carbon aerogel composites have been prepared by condensation polymerization and high temperature pyrolysis. The morphology of carbon aerogel is characterized by SEM. The pore structure is characterized by N₂ adsorption-desorption technique. The thermal insulation properties of carbon aerogel composites are tested. Carbon aerogel composites show good thermal insulation and high temperature resistance in inert atmosphere The results show that they are suitable for applications in aerospace thermal protection industry.

Abstract: In this study, the cellulose nanofiber (CNF) was prepared using carrot slag discarded from industrial carrot juice. The FTIR results of the carrot fiber show that the impurities such as lignin have been removed after alkali and acid neutralization treatment. In addition, it was confirmed that the carrot nanofiber was successfully prepared by the 2,2,6,6-tetramethylpiperidine (TEMPO) radical oxidation method. Subsequently, the obtained nanofiber was surface modified by styrene suspension polymerization and silane coupling agent, respectively. The results of water contact angle analysis show that the hydrophobicity of the modified nanofibers was improved. Moreover, a set of nanocomposite films were prepared by incorporating carrot nanofiber into sodium alginate (SA) and polystyrene (PS), respectively by using solution casting method. The obtained results showed that the TEMPO radical oxidized nanofiber containing film had the best transmittance in SA nanocomposite series. On the other hand, styrene suspension polymerization modified nanofiber containing one exhibited the best transparency in PS nanocomposite series.

Abstract: Nanocellulose fibers (NCF) is a renewable biodegradable polymer in nature. It has extensively interest as a reinforcement material in nanocomposites due to its nanoscale advantages. However, the efficiency of NCF dispersion in polymer matrix has limitation due to its self-agglomeration.The objective of this research was to prepare surface-modified NCF using three different acids; succinic anhydride, phthalic anhydride and citric acid. The molar ratios of acid to anhydroglucose units in NCF used in this work were 6:1, 8:1 and 10:1. The effects of acid types and molar ratios toward physical properties were studied. The results showed that succinic anhydride-modified NCF provided the highest DS range from 0.46-0.86. Dispersion of succinic anhydride-modified NCF provided good stability in water for 30 days. The succinic anhydride-modified NCF of 1:6 molar ratio is suitable for emulsion coating application.

Abstract: Joining carbon fibre reinforced composites with adhesive are widely used in various applications including aircraft structures and commercialized leisure products. However, surface contaminations hinder the adhesion of the bonding. Laser based surface treatment on bonding surface is suggested to improve the adhesion on the surfaces for secondary bonding. In this paper, single lap shear tests of the samples show that the laser pre-treated samples lead to the higher joint strength then acetone cleaned reference samples and surface sanded samples. The failure mode changed from adhesion failure in the reference sample to cohesion mode in the laser treated samples. The structure, topography and morphology of the composite surfaces which were pre-treated with laser radiation were observed. A correlation between surface properties and adhesive bonding strength was investigated. It should be noted that the variation of the pulse frequency level of the laser treatment contributed to the fibre breakage and the epoxy removal level of the sample surfaces.

Abstract: As its much lower thermal conductivity than other usual materials, Silica aerogel is a potentially efficient heat insulation material with the lowest bulk density. However, it is transparent for infrared light when used in high temperature. Herein, titanium oxide was added in the silica aerogel by in-situ blending. The dispersion property of titanium oxide particles, microstructure mechanical property, thermal conductivity, and thermal insulation were investigated. The results of this in-situ blending process indicated a potential application value in aerospace thermal protection industry.

Abstract: The aim of this study is to prepare green composites from poly (lactic acid) (PLA) and in-house epoxidized natural rubber (ENR) with coir fibers (CFs). In-house ENR with medium epoxidation degree (about 35 mole% epoxidation) was first prepared via ‘in situ’ epoxidation of natural rubber latex. PLA was melt-mixed with three loadings (10, 20 and 30 wt%) of ENR on a twin-screw extruder, followed by injection molding to observe their mechanical properties (impact strength, tensile strength, Young’s modulus and elongation at break) and thermal stability. The results showed that the addition of the ENR enhanced the impact strength and elongation at break, but deteriorated tensile strength, Young’s modulus and thermal stability of the blends. From mechanical properties consideration, the 90/10 PLA/ENR blend was selected for preparing green composites with different amounts of CFs (5, 10 and 20 phr). It was found that the incorporation of CFs improved tensile strength and Young’s modulus. However, the impact strength, elongation at break and thermal stability of the green composites decreased as compared to those of the neat 90/10 PLA/ENR blend.

Abstract: Poly(acrylic acid) (PAA) was grafted onto natural rubber (NR) to improve the compatibility of NR and poly(lactic acid) (PLA). Polymer blend between PLA and NR-g-PAA was prepared by an internal mixer. Fourier-transform infrared spectroscopy (FT-IR), tensile testing, impact testing, thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) were employed to determine the functional group, mechanical properties and thermal properties of blends, respectively. Results showed that the addition of NR-g-PAA significantly improved the elongation, impact strength and thermal stability of blends. The P70N30 was the optimum composition to obtain improved mechanical properties of PLA.

Abstract: This experiment was conducted to investigate thermal and mechanical properties of the biodegradable composites based on Poly (lactic acid) (PLA) incorporated with cellulose-graft-polystyrene (cellulose-g-PS) at 1, 3, 5 and 10 wt%. The modification of cellulose filler was confirmed by the T_d shifting of thermogravimetric analysis (TGA) thermogram from 334 to 348 °C and characteristic peaks corresponding to the styrene benzylic ring obtained from fourier-transform infrared spectroscopy (FTIR) analysis. The slight improvement of PLA properties with addition of 1 wt% of cellulose-g-PS composite probably was due to the good interaction and compatibility between filler and the matrix of polymer.