Development and thermal behaviour of ternary PLA matrix composites

Biodegradable PLA composites were prepared using microcrystalline cellulose (MCC) and silver (Ag) nanoparticles. The main objective of the present study is to develop new biopolymer composites with good mechanical properties, thermal stability, maintaining the optical transparency and also providing antimicrobial properties through silver nanoparticle introduction. Composites were prepared with 1%wt of Ag nanoparticles and 5%wt of MCC using a twin-screw microextruder; film parameters were optimized in order to obtain a thickness range between 20 and 60 μm.PLA composites maintained optical transparency properties of the matrix, while MCC was able to reduce polymer permeability. Thermal analysis revealed that MCC increased PLA crystallinity and the mechanical properties of the composites demonstrated that tensile modulus was improved by microcrystalline cellulose.     

Mechanical and thermal properties of epoxy/silicon carbide nanofiber composites

The silicon carbide (SiC) nanofibers (0.1, 0.25, and 0.5 phr), produced by self‐propagating high‐temperature synthesis (SHS), are used to reinforce the epoxy matrix cured with an anhydride hardener. Morphological studies reveal a better dispersion of SiC nanofibers and a good level of adhesion between nanofiber and the matrix in composites with lower (0.1 and 0.25 phr) nanofiber loading. The flexural studies show that a maximum increase in flexural properties is obtained for composites with 0.25 phr SiC nanofiber. The fracture toughness of epoxy is found to increase with the incorporation of SiC nanofibers, and 0.25 phr SiC nanofiber loading shows maximum fracture toughness value. The possible fracture mechanisms that exist in epoxy/SiC nanofiber composites have been investigated in detail. Thermogravimetric analysis reveals that SiC nanofibers are effective fillers to improve the thermal stability of epoxy matrix. Copyright © 2014 John Wiley & Sons, Ltd.     

Mechanical and thermal characterization of sisal fiber reinforced polylactic acid composites

The advantages of green composites are including, but not limited to their environmental friendly nature, lightweight, reduction of production energy and costs, and recyclability. This work focuses on the mechanical, thermal, and dynamic mechanical properties of biocomposites. For that purpose, biosourced polymers were used, namely polylactic acid (PLA) and sisal fiber, and biocomposites were extruded and then injection molded with different contents of sisal fibers (5%, 10%, 15%). The results show that the increase of the rate of reinforcement improves the mechanical and dynamic mechanical properties of the biocomposites made. By the increase of the sisal fiber content, the degree of crystallinity of the matrix was increased from 47% to 61%, as sisal fibers were acted as a nucleating agent for the PLA.     

Mechanical and thermal properties of green polylactide composites with natural fillers

Green composites of PLA with micropowders derived from agricultural by-products such as oat husks, cocoa shells, and apple solids that remain after pressing have been prepared by melt mixing. The thermal and mechanical properties of the composites, including the effect of matrix crystallization and plasticization with poly(propylene glycol), have been studied. All fillers nucleated PLA crystallization and decreased the cold-crystallization temperature. They also affected the mechanical properties of the compositions, increasing the modulus of elasticity but decreasing the elongation at break and tensile impact strength although with few exceptions. Plasticization of the PLA matrix improved the ductility of the composites.     

Water resistance,flame retardancy,and thermal properties of hydrophobic polypropylene/bamboo fiber composites

Journal of Thermal Analysis and Calorimetry - Melamine–formaldehyde resin-coated bamboo fiber (MFBF) and ammonium polyphosphate (MFAPP) were prepared, and then flame-retardant polypropylene...     

Synthesis and thermal behaviour of polyamide 6/bentonite/ammonium polyphosphate composites

In order to achieve acceptable levels of flame retardancy of polymers, phosphorus-based flame retardant (FR) additives at about 20-30% w/w are required which is too high for conventional synthetic fibres. To know whether more finely sized particles of conventional FRs with or without nanoclay are more effective at the same concentration, composites of PA6 with bentonite and ammonium polyphosphate (APP) have been prepared by melt processing in a twin-screw extruder. XRD peaks and TEM images of PA6/Org-bentonite composite show partially ordered intercalation and ordered exfoliation. Thermal analysis in He shows that thermal stability of PA6 nanocomposite has increased by 18 °C compared with pure PA6 during degradation after 425 °C but it has decreased by 100 °C on inclusion of APP in PA6/nanoclay composites. The char yield is increased by 20% in PA6/bentonite/APP composites. No effect on thermal stability or char yield is observed by reducing the particle size of APP.     

Structural effects on thermal properties and morphology in XLPE

This study investigated the morphological, thermal and mechanical changes with increasing crosslink density for two low density polyethylenes (LDPE). A reference LDPE was compared with an LDPE containing a higher number of vinyl groups that was introduced via a copolymerisation with a diene. During crosslinking, two reactions simultaneously occur in the copolymer, i.e. a reaction of the vinyl groups and combination crosslinking. After crosslinking with a low amount of peroxide, the majority of the crosslinks originate from reacted vinyl groups in the LDPE containing the higher number of vinyl groups, whereas the crosslinks in the reference LDPE originate from combination crosslinking, thus leading to different crosslinked structures for the two polymers. The melt temperature, crystallisation temperature, and degree of crystallinity were measured using a Differential Scanning Calorimeter. Thermal fractionation studies and morphology studies were also made. The Differential Scanning Calorimetry results show a decrease in those properties for both materials along with a concurrent change in the morphology when the crosslink density increased. The results deviate slightly between the materials.     

Mechanical,thermal, and ultraviolet resistance properties of polycarbonate/cerium oxide composites

The composites containing polycarbonate (PC) and cerium oxide (CeO₂) nanoparticles as well as nanoparticles modified with stearic acid (mCeO₂) have been prepared using a melt blending method. The composites are studied by using FTIR spectroscopy, differential scanning calorimetry, thermal gravimetric analysis and scanning electron microscopy, and their tensile strength and ultraviolet (UV) resistance are examined. The results indicate that the introduction of CeO₂ nanoparticles at 1 wt% can improve the mechanical properties of PC, while a weight ratio that is over 1 wt% can lead to a reduction in the tensile strength. Compared with the PC/CeO₂ composites, the PC/mCeO₂ composites provide better mechanical properties. Besides, the introduction of CeO₂ nanoparticles gives PC promising UV resistance. However, different amounts of CeO₂ nanoparticles used provide similar thermal and UV resistance in PC. In a comparison of the PC/CeO₂ and PC/mCeO₂ composites, there are no apparent differences observed between CeO₂ and mCeO₂ on improving the UV resistance of PC.     

Mechanical and thermal properties of (Ag/C nanocable)/epoxy resin composites

A novel Ag/C nanocable and epoxy resin composite was obtained by compounding Ag/C nanocables and epoxy resin. The nanocable is composed of a nanowire (core) wrapped with one or more outer layers (shell). Scanning electron microscopy images proved that the nanocables consisted of a silver nanowire core and a carbon outer shell. The Ag/C nanocables were modified by hyperbranched poly (amine ester) to improve their mechanical properties for further application. We separately compounded raw and modified Ag/C nanocables with epoxy resin, and then tested the thermal performance, tensile properties, and fracture morphology of each composite. We found that the tensile strengths of the two composite systems were enhanced by the epoxy resin, with the modified (Ag/C)/epoxy resin composite system improving more significantly. Differential scanning calorimeter (DSC) results showed that the glass transition temperature of the unmodified (Ag/C)/epoxy resin composite is increased when the Ag/C nanocable is filled, while that of the modified system slightly decreased. Fracture morphology results showed that both (Ag/C)/epoxy composite systems featured increased toughness. The modified Ag/C nanocables had better compatibility with the epoxy resin. The relationship between the properties and microstructure of the composites were discussed in detail to explain the mechanism behind the observed changes in material properties.     

Evaluation of the hybridization effect on the thermal and thermo-oxidative stability of bamboo/kenaf/epoxy hybrid composites

Bamboo-/kenaf-reinforced epoxy hybrid composites were prepared by hand layup method. The aim of this study is to look into the hybridization effect of bamboo and kenaf fibers at different ratios on thermal and thermo-oxidative (TOD) stabilities of hybrid composites. Three types of hybrid composites were fabricated with different mass ratios of bamboo fiber mat (B) to kenaf fiber mat (K), namely B/K 70:30, B/K 50:50 and B/K 70:30 while maintaining total fiber loading of 40% by mass. The thermal stability and thermo-oxidative (TOD) stability were analyzed by thermogravimetric analyzer. Differential scanning calorimetry (DSC) was used to investigate the oxidation onset temperature (OOT) of all the composites. The results reveal that bamboo composite shows higher thermal stability than kenaf composite in both inert and oxidative atmospheres. An increase in bamboo fibers mass ratio in the hybrid composite improved the thermal and TOD stability. The thermal and TOD stabilities of the hybrid composites follow the sequence of B/K 70: 30?>?B/K 50:50?>?B/K 30:70. Pure epoxy composite recorded the highest OOT at 197.50 °C. The results show that the addition of natural fiber in the epoxy matrix has significantly reduced the OOT compared to the pure epoxy. Data obtained from this work will help us to fabricate a sustainable and biodegradable component for automotive or building materials.

     

Mechanical, thermal, and fire properties of polylactide/starch blend/clay composites

Polylactide (PLA)/starch blend/clay and PLA/clay composites are prepared by melt blending. Structural and thermal characterizations are performed by differential scanning calorimetry, X-ray diffraction analysis, and thermogravimetric analysis. The fire properties are assessed on a dual cone calorimeter. Combustion residue and char formation is characterized by optical microscopy and attenuated total reflection infrared spectroscopy. Although the clay is not fully intercalated/exfoliated, the composites exhibit a higher thermal stability and much reduced peak heat release rate, and the PLA/starch blend composite retains its mechanical properties. For the PLA/starch blend composite, smoke release is also considerably reduced. Catalyzed, oxidative decomposition is shown to occur early in the thermal decomposition of the composites, prior to increased thermal stability. The inclusion of clay promotes char formation and increases the quantity of carbonaceous char in the combustion residue. There is minimal migration of the clay to the surface prior to ignition and char is formed mainly after ignition and during burning. During the later stages of burning some of the char formed is converted to CO₂.     

Mechanical behaviour analysis of the interface in single hemp yarn composites: DIC measurements and FEM calculations

The present work aims to investigate the local deformation mechanisms around a yarn in an eco-composite. Different hemp yarn orientations and two types of epoxy resin were tested. Full-field measurements were realised with the digital image correlation technique on specific single yarn composites, either on the face of the specimens, or on the edge. The tensile tests were performed under an optical microscope to give sufficient precision, and a numerical model was developed. The experimental results showed high heterogeneities in strain fields which increase with the applied stress level. The comparison with the underlying microstructure and the numerical model enabled us to study the influence of the yarn on the mechanical behaviour. The local constitutive behaviour of the different constituents of the specimens could be approached by these analyses. These results constitute a complete and original database on hemp/epoxy interface mechanical behaviour.     

Mechanical and thermal properties and flame retardancy of phosphorus-containing polyhedral oligomeric silsesquioxane (DOPO-POSS)/polycarbonate composites

A novel polyhedral oligomeric silsesquioxane containing 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO-POSS) has been incorporated into polycarbonate (PC) composites in order to study its effect on mechanical and thermal properties and flame retardancy. The mechanical and thermal properties of the DOPO-POSS/PC composites have been investigated by tensile and flexural testing, DSC, and DMA. Slight enhancements of yield stress, and flexural strength and modulus, and obvious decreases of fracture strength and strain of the DOPO-POSS/PC composites were observed with an increase in DOPO-POSS loading. The glass transition temperatures (T_g) of the composites were reduced with increasing DOPO-POSS loading. The morphology of the PC composites was evaluated by SEM, which indicated that the DOPO-POSS was dispersed with a particle size of 100-250 nm in the PC matrix. The thermal degradation behaviour and flame retardancies of PC composites with different DOPO-POSS loadings were investigated by TGA, LOI, UL-94 standard, and cone calorimetry. The composite had an LOI value of 30.5 and a UL-94 rating V-0 when the content of DOPO-POSS was 4%.     

Viscoelastic behaviour of rubberwood-polymer composites

The dynamic storage modulus E' of rubberwood (Hevea braziliensis) increased after the in situ polymerization of methylmethacrylate in the wood cellular structure. A significant linear relationship existed between the percentage increase in E' and polymer loading. A thermal scan of tan δ values between -120° and 200°C revealed that the damping pattern of rubberwood was affected to different extents by three different polymeric systems. Poly(styrene-co-acrylonitrile) caused the greatest change in the damping pattern, followed by polymethylmethacrylate-dioxane, and polymethylmethacrylate. This observed trend was attributed to the relative extent of monomer penetration and interaction with the wood cell-wall components.     

An analysis of the thermal aging behaviour in high-performance energetic composites through the glass transition temperature

Differential scanning calorimetry (DSC) was used to analyze the thermal aging behaviour in energetic composite materials where a hydroxyl-terminated polybutadiene (HTPB)/isophorone diisocyanate elastomer is the polymeric matrix. Different parameters from the analysis of the glass transition, such as the glass transition temperature (T_g), were used in order to monitor this isothermal aging at 65 °C during a total time of 3000 h, finding an increasing and broadening T_g. In addition, the accelerated aging behaviour of these materials was also studied by a classical method, based on the change of mechanical properties such as those of Young's modulus or strain at break. The correlation between both methodologies was examined, demonstrating that an analytical technique such as DSC allows the evaluation of the actual state of composite solid propellants with a small sample and a straightforward measurement.     

Thermal behaviour of composites aluminosilicate-calcium phosphates

A new type of aluminosilicate matrix calcium phosphate crystallites composites (ACPC) was synthesized and studied for osseous bone applications. The room temperature synthesis of the aluminosilicate matrix and composites was described. Thermal treatments of compounds allowed the adaptability of some parameters (pH, porosity and mechanical properties). Structure of heat treated composites were characterized by XRD and FTIR. The influence of thermal treatment on the mechanical properties, the porosity and the pH was studied for two temperatures (250 and 500°C). Results evidenced the ability to control the pH, the high level of porosity (»70%) and the good mechanical properties, allowing to consider that ACPC are potential biomaterials for osseous bone application.     

Thermal behaviour of gypsum based composites

DTA/TG and X-ray investigations were carried out on different building composites in order to examine their relative hydration processes. The presence of lime, hemihydrate gypsum, ferosilicate, and some other wastes as leaner and hydrophobic additive in different proportions into composites provokes hydration reactions, leading to calcium silicate hydrate (CSH), ettringite and an intermediate phase formation with varying chemical composition of calcium, aluminum, silicon and sulfur. DTA curves indicate several transformations taking place between composites components, related to hydration of some phases. The content of ettringite component corresponds to the properties and it is used as an indicator for the possibility of industrial application. It is found out that gypsum based cementitious binders could be used as building material in the industry. The same time it is confirmed that the selected wastes could be considered as secondary raw materials.     

Comparison of antioxidants for combined radiation and thermal aging and superposition of radiation and thermal aging for EPR and XLPE

Thermal and combined thermal and radiation aging of low voltage EPR and XLPE cable insulation with Agerite MA antioxidant and with the ZMTI/Aminox antioxidant system was examined to compare the relative effectiveness of the antioxidant and polymer systems. All provided significant stability with no clear choice of any particular combination being superior to the others. A comparison of degradation from thermal and radiation aging with degradation from combined thermal/radiation aging showed that the damage from the individual aging effects was superposable. This indicates that synergistic effects have little importance for the EPRs and XLPEs tested under the aging conditions observed.     

Mechanical and thermal properties of Acacia leucophloea fiber/epoxy composites: Influence of fiber loading and alkali treatment

In this work, the influence of fiber content and alkali treatment on the mechanical and thermal properties of Acacia leucophloea fiber-reinforced epoxy composites was studied. Ten composite samples were fabricated by varying fiber content (5, 10, 15, 20, and 25 wt%); both untreated and treated fiber were soaked in a 5% NaOH solution for 45 min by using hand-layup method. The composite reinforced with 20 wt% treated fiber content exhibited better mechanical properties and thermal properties. Fourier transform infrared analysis, morphological analysis by atomic force microscope, and scanning electron microscope of composites were also performed.