Cellulose nanocrystal treatment of aligned short hemp fibre mats for reinforcement in polypropylene matrix composites

Cellulose - Oriented short hemp fibre mats were produced using dynamic sheet forming (DSF) incorporating cellulose nanocrystals (CNCs) to improve their integrity. The CNCs were found to act as a...     

Investigations on the recycling of hemp and sisal fibre reinforced polypropylene composites

Microscopic, mechanical, rheological and thermal tests were carried out in order to determine the recycling behaviour of PP/vegetal fibre composites. Different composites using hemp and sisal were characterized. All results were compared with PP-g-MA/hemp composites and PP/glass fibre composites.The results prove that mechanical properties are well conserved with the reprocessing of PP/vegetal fibre composites but that there is poor adhesion between the fibres and PP without any treatment. The addition of PP-g-MA shows an improvement of the bonding evidenced by MEB pictures. Vegetal fibres induce an increase in the percentage of crystallinity χ_c and in the crystallization temperature T_c which can be explained by the nucleating ability of the fibres improving crystallization of PP. The Newtonian viscosity η₀ decreases with cycles, indicating a decrease in molecular weight and chain scissions induced by reprocessing. The decrease of fibre length with reprocessing could be another reason for viscosity decrease.     

Thermal and crystallization studies of short flax fibre reinforced polypropylene matrix composites: Effect of treatments

The effect of fibre treatments on thermal stability of flax fibre and crystallization of flax fibre/polypropylene composites was investigated. For thermal stability study, flax fibres have been treated using maleic anhydride, maleic anhydride polypropylene copolymer, vinyltrimethoxy silane and alkalization. In order to compare thermal stability of flax fibres thermogravimetry (TG) analysis has been used. Kinetic parameters have been determined by Kissinger method. Results showed that all treatments improved thermal stability of flax fibres. For crystallinity analysis, three different techniques have been used, differential scanning calorimetry analysis (DSC), pressure–volume–temperature (PVT) measurements for analysis of volume shrinkage and polarized optical microscopy (POM). All techniques results showed that addition of flax fibre increased crystallization rate. Besides, depending on fibre surface treatment and crystallization temperature, flax fibre/PP composites can show transcrystallinity.     

Effect of l-Arginine treatment on the in vitro stability of electrospun aligned chitosan nanofiber mats

Chitosan (Cs) mats obtained by electrospinning are potentially ideal scaffolds for tissue engineering. This technique allows obtaining nanometric fibrous structures with preferred orientation, which in turn enable cells to align themselves and produce extracellular matrix along desired orientations. In this study, we fabricated aligned Cs electrospun nanofiber mats and investigated the role of the amino acid l-Arginine (L-Arg) as stabilizing agent. Morphological, chemical, mechanical and biological characterizations were performed on untreated and L-Arg treated nanofibrous mats showing the role of L-Arg as biomimetic stabilizer. L-Arg acts as chemical stabilizer of nanofibrous mats, providing improved wettability behavior, mechanical properties and stability even after 60 days in aqueous medium in comparison to untreated mats. Moreover, preliminary biological tests demonstrated favorable cell-material interactions implying physiological responses in terms of viability and proliferation. The proposed L-Arg-treated Cs mats can be considered as potential scaffolds for highly oriented tissue patterning.     

Structure and thermal properties of stearic acid/silica composites as form-stable phase change materials

In this study, stearic acid/silica phase change composites were prepared by the sol-gel method using stearic acid as phase change materials (PCMs). The effects of mass fraction of stearic acid were comprehensively investigated. The structures and thermal properties of the obtained composites were characterized by various methods, including scanning electron microscopy (SEM), differential scanning calorimetry (DSC), leakage tests, and thermogravimetry analysis (TG). The results indicated that composite containing 76% stearic acid had the best thermal properties and low mass leakage, making 76% stearic acid as the maximum content that silica matrix could protect in the composites. The latter was further confirmed by morphological analyses of the silica matrix. Silica matrix exhibited spherical particle clusters, following big–small–big–small size pattern as stearic acid rose. The composite with 76% stearic acid was at the key point of change in particle size. These findings look promising for future to prepare silica-based phase change composites with good thermal properties easily.

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Characterization of the coating layer on glass fibre used as reinforcement in polyepoxyde matrix

R glass fibre for the reinforcement of epoxy matrices has been coated with epoxy prepolymer (as film-former or sizing agent) or γAPS aminosilane (as coupling agent) or a mixture of these two products. The structure of the coating layer and its interaction capabilities with fibre and matrix have been studied by coupled calorimetry-gravimetry of sorption of different model reactants and by Fourier Transform infra-red analysis.     

Influence of accelerated ageing on the physico-mechanical properties of alkali-treated industrial hemp fibre reinforced poly(lactic acid) (PLA) composites

30 wt% aligned untreated long hemp fibre/PLA (AUL) and aligned alkali treated long hemp fibre/PLA (AAL) composites were produced by film stacking and subjected to accelerated ageing. Accelerated ageing was carried out using UV irradiation and water spray at 50 °C for four different time intervals (250, 500, 750 and 1000 h). After accelerated ageing, tensile strength (TS), flexural strength, Young's modulus (YM), flexural modulus and mode I fracture toughness (K_Ic) were found to decrease and impact strength (IS) was found to increase for both AUL and AAL composites. AUL composites had greatest overall reduction in mechanical properties than that for AAL composites upon exposure to accelerated ageing environment. FTIR analysis and crystallinity contents of the accelerated aged composites support the results of the deterioration of mechanical properties upon exposure to accelerated ageing environment.     

Thermoplastic composites based on flax fibres and polypropylene: Influence of fibre length and fibre volume fraction on mechanical properties

Natural-fibre-mat-reinforced thermoplastic (NMT) composites based on flax fibre mats and a Polypropylene (PP) matrix were manufactured using (i) a film-stacking method and (ii) a paper making process. The influence of fibre length and fibre content on stiffness and strength is reported and compared with data for glass-mat-reinforced thermoplastic (GMT) composites, including the influence of using maleic-anhydride grafted PP. The data is also compared with existing micromechanical models like Kelly-Tyson and Cox-Krenchel for strength and stiffness, respectively. A good agreement was found between theory and experiment in case of stiffness while in case of strength the experimental values fall well below the theoretical predictions. Results indicated that NMTs are of interest for low-cost engineering applications and can compete with commercial GMTs, especially when a high stiffness per unit weight is desirable. Results also indicated that the key area for future development lies not only in improved adhesion but mainly in improving the fibre strength.     

Effect of gamma irradiation and fiber surface treatment on the properties of bagasse fiber-reinforced waste polypropylene composites

Biocomposites of waste polypropylene (WPP) with bagasse fiber as reinforcing component can be readily prepared based on waste management application. Bagasse was subjected to chemical treatments using sodium hydroxide (NaOH) and vinyl triethoxysilane to modify the fiber properties. Scanning electron microscope and Fourier-transform infrared spectroscopy were used to elucidate fiber modification after treatments. Compounding of WPP at various ratios of bagasse was produced by melt mixing. Treated and untreated fiber composites were investigated under conditions of gamma irradiation at 20?kGy. In general behavior, at different fiber loadings, treated biocomposites have better properties than untreated one and fiber treated with silane is the best. Furthermore, treated biocomposites represented more biodegradability under soil than untreated one. The results of mechanical properties showed that the as-prepared fiber composites have superior irradiation-resistant properties.     

Functionalization of graphene oxide with different diisocyanates and their use as a reinforcement in waterborne polyurethane composites

Abstract

To examine the reinforcing effects of isocyanated graphene oxide (NCO-GO) on a waterborne polyurethane matrix, the surface of GO was respectively modified by isophorone diisocyanate (IPDI), hexamethylene diisocyanate (HDI) and toluene diisocyanates (TDI) and then confirmed by FT-IR, Raman, TGA, XRD, TEM, AFM and SEM-EDS. The dispersity behavior between different NCO-GO and polymer was evaluated by FESEM and XRD. The nanocomposites’ chemical structure, emulsion morphology, hydrophobicity, thermal and mechanical properties were investigated by FT-IR, TEM, TGA, tensile testing machine and water contact angle test, respectively. It was shown that these properties of nanocomposites including tensile strength, initial thermal degradation and hydrophobicity were increased by the incorporation of NCO-GO, in which, particularly, the tensile stress and initial degradation temperature were respectively increased from 13.32 to 18.80?Mpa and 249 to 288?°C after the addition of TDI-GO. These superior reinforcing effects were attributed to the two-dimensional structure of NCO-GO as well as the good interfacial adhesion between the NCO-GO and WPU matrix.     

Conformational properties of macromolecular pyramoids and their potential use as nano-containers

We study the macroscopic behavior of a pyramid-like nano-construct made of linear macromolecular chains. The average mean square end-to-end distances of the six edges of the pyramoid are evaluated by means of the Gaussian chain model and are found smaller than those of free chains because of architecture confinement. We also evaluate the average areas of the four faces which give a first estimate of the open windows towards the interior space of the macromolecular construct and its loading capacity. The average volume of the polymeric nano-container, which provides a measure of its interior emptiness and carrying ability, is estimated as well. The density of monomers at each point of the construct shows the three-dimensional character of the nano-cage and the location of its entrances and voids.     

Grafting polypropylene and treatment of calcium carbonate to improve structure and properties of polypropylene composites

In this paper, calcium carbonate was chemically treated with two kinds of dicarboxylic acids before compounding with polypropylene in the presence of dicumyl peroxide (DCP). It was observed that the mixture of dicarboxylic acids could improve the crystallization and impact strength properties of calcium carbonate/polypropylene composite. With further addition of DCP, more PP-g-MA was produced in the blend, resulting in PP composites with larger β-phase content and improved mechanical properties. In the experiments, the maximum K _β value of 52.0 % was obtained. The elongation at break of composite increased from 252 % for PP composite with untreated calcium carbonate to 444 % for PP composite with chemically treated calcium carbonate.     

Effect of the polymer matrix on the properties of advanced composites

The relationships discussed here clearly show that for the development of composite materials a multidisciplinary approach encompassing polymer chemistry, physics, engineering and material science is necessary. The complex composition of fiber reinforced polymeric composite materials, involving the synergistic interplay of individual components, requires new methods for the development of materials, which are not solely based on the formulation chemistry of the components. In the future, resistance against the application of advanced composites must be reduced, by gaining more confidence in the performance of this new class of materials with a fundamental understanding of their properties and potential. It will thus be possible to abolish unreasonable test methods and to use design characteristics which take maximum advantage of this material class.     

Analysis of the use of an industrial waste as reinforcement in epoxy composites

A study was done to investigate the use of the waste generated at a hydrometallurgical zinc plant as filler in epoxy matrix composites. The waste was processed before its incorporation into the matrix and composites with volume fraction from 10 to 50% were fabricated with six different particle sizes. The results show that the mechanical properties increase with the decrease of the particle size until a threshold value is reached. Below this value the distance between particles became the controlling parameter. The results also show that this waste can be satisfactorily used as filler. Its advantages over commonly used fillers are its low cost and the environmental gain of its convenient disposal.     

Effect of compatibilisers on mechanical and thermal properties of bentonite filled polypropylene composites

Bentonite filled polypropylene composites were prepared using a Polydrive Thermo Haake, internal mixer at 180 °C and at 50 rpm of rotor speed. Effect of compatibilisers on mechanical, thermal, water absorption and morphological properties of bentonite filled polypropylene composites was investigated. Two types of compatibilisers namely, palm oil fatty acid additive (POFA) and polypropylene grafted-maleic anhydride (PPMAH) have been used in this study. The mixing of the composites improved with the addition of POFA. The impact strength and elongation at break increased with the presence of both compatibilisers whilst, tensile strength and Young's modulus improved only with addition of PPMAH. Morphological investigation using SEM revealed that the improvement in impact strength and elongation at break was due to enhancement of the interfacial adhesion between bentonite and PP. The thermal stability of bentonite filled PP improved with the incorporation of POFA and PPMAH. Less percentage of water absorption has been observed in PP-bentonite system with PPMAH.     

Study of the wettability properties of polypropylene nonwoven mats by low‐pressure oxygen plasma treatment

Surface modification by plasma treatment is widely used for textiles and polymeric materials. Plasma processes are environmentally friendly and reduce chemicals and energy consumption. This study reports the effect of cold, low‐pressure oxygen plasma on the wettability properties of polypropylene (PP) nonwoven mats. The wetting properties were examined using contact angle, surface energy, and diameters of the drop after 20 s of treatment. It was found that plasma treatment had a significant effect on the wettability of PP fibers. The ageing for 90 days had no significant effect on the wettability. It was also shown that the morphology of the fibers was not affected by the plasma treatment. Copyright © 2007 John Wiley & Sons, Ltd.     

The effects of cauliflower-like short carbon fibers on the mechanical properties of rigid polyurethane matrix composites

Stress concentration and weak interfacial strength affect the mechanical properties of short carbon fibers (CFs) reinforced polymer composites. In this work, the cauliflower-like short carbon fibers (CCFs) were prepared and the point was to illuminate the effects of fiber morphology on the mechanical properties of the CCFs/rigid polyurethane (RPU) composites. The results indicated that the surface structure of CCFs could increase the surface roughness of the fibers and the contact area between fibers and matrix, thereby promoting the formation of irregular interface. Compared with pure RPU and initial CFs/RPU composites, the strength and toughness of CCFs/RPU composites were simultaneously improved. The satisfactory performance was attributed to the special fibers structure, which played an anchoring role and consumed more energy during crack propagation.     

Surface treatment of langmuir-blodgett layers of poly (3-hexadecylthiophene) and stearic acid and their properties oaffected by gases

The influence of certain gases on the properties of thermally treated and -irradiated Langmuir-Blodgett (LB) films of poly (3-hexadecylthiophene) and stearic acid has been studied. Both the heat and -radiation brought about some structural surface layer changes, leading to temporal variations of the course of the in-plane conductivity of films affected by the presence of applied gases.     

Investigations of the microchemistry of interlayers in fibre/matrix composites

The potential applicability of analytical transmission electron microscopy is demonstrated for the characterization of the microchemistry of interlayers in fibre-reinforced composites with glass matrices.