Static and Dynamic Mechanical Properties of Vinylester Resin Matrix Composites Filled with Fly Ash

Summary: Vinylester resin matrix composites were prepared with a fly ash loading of 30, 40, 50 and 60 wt.‐%. Flexural properties of the composites were investigated. It was found that the flexural strength was lowered in all the filled composites, but the flexural modulus showed a significant increase of 10, 57, 112% in case of 30, 40 and 50 wt.‐% fly‐ash‐loaded composites respectively, compared to the neat resin. However, there was a decrease in the mechanical properties in case of 60 wt.‐% fly‐ash‐filled composites. The dynamic mechanical analysis was carried out to obtain information about the matrix‐filler interaction at the interface. The storage modulus value at room temperature was highest for the 50 wt.‐% fly‐ash‐filled composites, corroborating with the observed flexural modulus value. The fractured surfaces were examined under SEM and were correlated with the mechanical properties.

Large voids evident in the 60 wt.‐% fly‐ash‐filled composites.     

Correlation between Composition,Structure and Properties of Poly(lactic acid)/Polyadipate‐Based Nano‐Biocomposites

Poly(lactic acid) plasticized with 15 and 20 wt.‐% of polyadipate was melt‐blended with different amounts of an O‐MMT (1–5 wt.‐%) to prepare nano‐biocomposites. The effect of plasticizer and nanofiller contents on the morphology and on thermal, mechanical and barrier properties of PLA‐based nano‐biocomposites was evaluated in order to understand their structure‐properties relationships. The oxygen transmission rate was notably reduced (around 45%) with increasing amount of clay due to an increased tortuosity. However, for clay concentrations above 3 wt.‐%, a significant detriment in ductile properties could also be observed. For a given amount of nanofiller, the increasing plasticizer concentration improved the clay dispersion through the polymeric matrix.

     

Comparative Characterization of PP Nano‐ and Microcomposites by In‐Mold Shrinkage Measurements and Structural Characteristics

Poly(propylene)‐clay nanocomposites and poly(propylene) containing conventional inorganic fillers such as calcium carbonate (CaCO₃) and glass fiber were used in a comparative study focusing on dimensional stability, structure, mechanical and thermal properties. Micro‐ and nanocomposites were prepared by melt blending in a twin‐screw extruder. The relative influence of each filler was observed from dimensional stability measurements and structural analysis by WAXD, TEM, and thermal and mechanical properties. At equal filler loadings, PP/clay nanocomposites exhibit an improvement in dimensional stability and were the only composites capable of reduced shrinkage in both in‐flow and cross‐flow directions. The flexural modulus of PP increased nearly 20% by compounding with 4% organoclay, as compared to a similar performance obtained by compounding with 10 wt.‐% of CaCO₃ or approximately 6 wt.‐% of glass fiber. The HDT and thermal stability of PP were enhanced by using nanoclay as filler.

     

Effect of Comonomer Content on the Behavior of Propylene Copolymer/Compatibilizer/Clay Nanocomposites

A set of isotactic propylene copolymers with either 1‐hexene or 1‐octadecene were synthesized using a metallocene catalyst, and their nanocomposites with 5 wt.‐% of clay and 15 wt.‐% of compatibilizer were prepared and characterized. Clay intercalation and dispertion depend on the comonomer content in the matrix which improves at high short‐chain‐branching levels. The presence of both clay and compatibilizer increased the crystallization temperature of the matrix. A strong correlation between the elastic modulus of the matrix and its relative increase in the nanocomposite was observed. By adding clay and compatibilizer to the copolymer, the modulus can be increased by a factor of two. The results open new perspectives in the understanding of the effect of polyolefin topology on nanocomposites properties.

     

Chemically Extracted Cornhusk Fibers as Reinforcement in Light‐Weight Poly(propylene) Composites

Flexural, impact resistance, tensile, and sound absorption properties of composites from cornhusk fiber (CHF) and PP have been investigated. The effect of holding temperature, CHF length, CHF concentration, and enzyme treatment of CHF on mechanical properties and the effect of the latter two on sound absorption have been studied. Compared with jute/PP composites, CHF/PP composites have similar impact resistance, 33% higher flexural strength, 71% lower flexural modulus, 43% higher tensile strength, 54% lower tensile modulus, and slightly higher noise reduction coefficient. Enzyme treatment of CHF results in increased mechanical and sound absorption properties.

     

Nylon 6‐Polyesteramide Block Copolymers (NBC) and NBC/Phenolic Resin Composites, 1

Summary: A series of NBC/phenolic resin composites, containing 0, 1, 3, 5 or 7 wt.‐% of a powdered phenolic resin of different particle diameter, was prepared by the reaction injection molding (RIM) process. It was determined by SEM analysis that there exists a strong interaction between particles and matrix and that such interaction occurs through hydrogen‐type bonds as determined by FTIR analysis. According to the results it is thought that the glass transition temperature of the NBC/phenolic resin composites depends on two competing factors: the rigidity promoted by the hard solid filler and the flexibility imparted by the nylon 6 amorphous phase, whose proportion becomes more important with increasing amounts of phenolic resin particles. The elastic and flexural moduli of the NBC were improved by the addition of phenolic resin confirming the reinforcing effect of this filler. On the contrary, the impact strength diminishes with increasing amounts of phenolic resin, although this property is strongly dependent on the particle diameter.

SEM micrograph of the nylon 6‐polyesteramide block copolymer (80/20).     

Biocomposites Made from Short Abaca Fiber and Biodegradable Polyesters

Natural fiber‐reinforced biodegradable polyester composites were prepared from biodegradable polyesters and surface‐untreated or ‐treated abaca fibers (length ca. 5 mm) by melt mixing and subsequent injection molding. Poly(butylene succinate)(PBS), polyestercarbonate (PEC)/poly(lactic acid)(PLA) blend, and PLA were used as biodegradable polyesters. Esterifications using acetic anhydride and butyric anhydride, alkali treatment, and cyanoethylation were performed as surface treatments on the fiber. The flexural moduli of all the fiber‐reinforced composites increased with fiber content. The effect of the surface treatment on the flexural modulus of the fiber‐reinforced composites was not so pronounced. The flexural strength of PBS composites increased with fiber content, and esterification of the fiber by butyric anhydride gave the best result. For the PEC/PLA composites, flexural strength increased slightly with increased fiber content (0–20 wt.‐%) in the case of using untreated fiber, while it increased considerably in the case of using the fiber esterified by butyric anhydride. For the PLA composite, flexural strength did not increase with the fiber reinforcement. The result of soil‐burial tests showed that the composites using untreated fiber have a higher weight loss than both the neat resin and the composites made using acetylated fiber.

Flexural modulus of PBS composites as a function of fiber content.     

Improvement of Flex‐Fatigue Life of Carbon‐Black‐Filled Styrene‐Butadiene Rubber by Addition of Nanodispersed Clay

Summary: The flex‐fatigue life of carbon‐black‐filled SBR was dramatically improved by incorporation of 4–5 phr nanodispersed clay. Addition of clay did not decrease the degree of crosslinking of the composite but improved the hysteresis and tearing energy. ESEM observation of the flexing‐fracture morphology indicated that nanodispersed clay layers had the advantage over carbon black in that they could blunt the crack.

Effect of the clay amount on the flex fatigue life of the composites.     

Morphology and Thermal Stability of Novolac Phenolic Resin/Clay Nanocomposites Prepared via Solution High‐Shear Mixing

Phenolic resin/clay composites were prepared by high‐shear mixing of clay suspended in CH₃OH solutions of Novolac resin and curing agent. Pure clay Cloisite Na⁺ and pillared clays Cloisite 10A, 30B, and Na⁺Cloisite that was pillared by 3‐hexadecyl‐1‐methylimidazolium bromide were studied. After CH₃OH evaporation, Novolac was cured at low temperatures. XRD showed that clay gallery d‐spacings decreased upon solvent evaporation and partial curing. Slight d‐spacing increases were sometimes observed from a partially cured stage to a further cured composite. Na⁺Cloisite gave the highest nanodispersion, Cloisites 10A and 30B the lowest. TGA revealed that Na⁺ clay or organoclay incorporation in partially cured and cured composites did not improve the thermal stability of Novolac.

     

Phosphorus and Silicon Containing Low‐Melting Organic–Inorganic Glasses Improve Flame Retardancy of Epoxy/Clay Composites

New low‐melting organic–inorganic glassy polymers containing phosphorus and silicon are synthesized by the reaction between phenylphosphonic acid and methyltrichlorosilane or methyltriethoxysilane. They possess both low‐softening points and high onset decomposition temperatures, which are favorable for preparing flame retardant composites. Although the glass by itself is sensitive to water, the composites are not significantly affected in that way. For glass/clay/epoxy composites glass transition temperature (T_g) as well as storage modulus increase with the glass amount. The glasses improve flame retardancy significantly due to flame inhibition and the formation of fire residue working as protection layer during burning. The total heat evolved is reduced by 23–28% for using 5–15 wt.% glass and the maximum HRR even by 58–48%. The latter effect decreases with increasing glass amount due to an adulterate residue deformation. The combination of glass and clay is proposed as a possible route to enhance flame retardancy.

     

Synthesis and Characterization of Novel Polyurethane Composites Based on Hybrid Inorganic/Organic Phosphazene‐Containing Microspheres

Novel polyurethane (PU) composites were prepared, based on hybrid inorganic/organic phosphazene‐containing microspheres. The FT‐IR spectra have shown that the microspheres have been linked with PU matrix. The microstructure of the composites is investigated by SEM. In comparison with PU, the glass transition temperatures and thermal stability of the composites are increased. The results from tensile testing of the composites have indicated that tensile strength is improved and elongation at break is almost invariable. The investigation on the surface properties of the composites showed that the water contact angles are obviously increased by adding 2 and 4 wt.‐% microspheres to the matrix.

     

Transparent and Conductive Graphene Oxide/Poly(ethylene glycol) diacrylate Coatings Obtained by Photopolymerization

Water‐dispersed graphene oxide sheets were used to prepare graphene/poly(ethylene glycol) diacrylate resin composites by photopolymerization. It was found that graphene sheets undergo excellent morphological distribution within the resin system, giving rise to transparent composites with unaltered thermal properties with respect to the neat resin, that are electrically conductive at loading ratios as low as 0.02 wt.‐% of graphene oxide. The proposed strategy based on photopolymerization provides an easy, energy‐saving and environmental friendly technique that can find a wide application in coating technology, mainly for electromagnetic shielding and antistatic coatings.

     

Cationic UV‐Curable Conductive Composites from Exfoliated Graphite

Electrically conductive, cationically UV‐cured composites were prepared using exfoliated graphite plates (EGP) with cycloaliphatic epoxy resin and polyalcohol binder system. Exfoliated graphite (EG) was obtained from natural flake graphite through chemical and thermal treatment. Sonication of EG in solvent produced EGP. Characterization of graphite samples by XRD showed structural similarity between original graphite and EGP. UV curing behavior was characterized using photoDSC. Electrical resistivity measurements of the composites as a function of EGP concentration showed that at low filler concentration the binder system can influence the electrical percolation behavior. Some formulations showed electrical percolation at less than 1 vol.‐% of EGP filler.

     

A New Class of Injection Moulded Structural Biocomposites from PHBV Bioplastic and Carbon Fibre

Biocomposites from carbon fibre (CF) and poly(hydroxybutyrate‐co‐hydroxyvalerate) (PHBV) bioplastic were fabricated by extrusion followed by injection moulding. The effects of fibre length and fibre loading on the performance of PHBV/CF composites were investigated. The amount of CF (for both 150 µm and 6 mm length) was varied from 10 to 40 wt.‐%. The significant improvement in tensile strength (65%) and flexural strength (96%) was observed at 30 wt.‐% CF (6 mm length) loading. The heat deflection temperature (HDT) of the PHBV/CF composites increased by 32% compared to neat PHBV. The fibre–matrix interaction was analysed using scanning electron microscopy (SEM). The tensile modulus of the composites was evaluated theoretically by the rule of mixture and the Hirsch model.

     

Formation of Thermosets via Molecular Pockets in Thermoplastic Chains: A Simple and Direct Way to Nanospherical Thermosets

By curing bisphenol A‐based benzoxazine in a thermoplastic polystyrene‐block‐poly (ethylene‐co‐1‐butene)‐block‐polystyrene (SEBS) block copolymer, nanospherical polybenzoxazines as small as 150 nm with narrow size distribution are obtained in high yield. This specific condition allows simple and direct formation of nano‐ or microspherical thermoset resins. A model of how the thermoplastic block copolymer chains act as a molecular pocket where the thermoset curing proceeds is presented. It is demonstrated that this mechanism requires (i) a particular block of thermoplastic copolymer which allows specific interaction with monomeric thermoset molecules, and (ii) the curing of thermosets in a molecular assembly structure to confine the phase separation of thermoset prepolymer during curing.

     

Mechanical Properties of Hemp‐Fibre‐Reinforced Euphorbia Composites

A composite material consisting of hydroxide‐modified hemp fibres and euphorbia resin was produced. The composites were tested in tension, short‐beam interlaminar shear stress and in impact. There was an increase in the tensile strength and modulus for resins with high‐hydroxyl‐group based composites. Similar results were obtained for interlaminar shear stress while low‐hydroxyl group euphorbia resin based composites exhibited high impact strength. The euphorbia resin with high hydroxyl content yielded composites with high stiffness. The use of euphorbia‐based resins in composite manufacture increases the value of the euphorbia oil as well as creating a new route of composite manufacturing.

     

Mechanical Performance of Soy‐Hull‐Reinforced Bioplastic Green Composites: A Comparison with Polypropylene Composites

A blend composition of poly(3‐hydroxybutyrate‐co‐valerate) and polylactide is used as a bioplastic matrix and reinforced with soy hull to engineer novel green composites. A comparative study with soy‐hull‐reinforced polypropylene composite system is performed. A compatibilizer is used to engineer the novel class of green composites with a balanced stiffness and toughness performance with the target to substitute PP‐based composites. The flexural and impact strength along with hydrophobicity of compatibilized composites are improved significantly over the noncompatibilized counterpart. The fiber/matrix interaction is investigated by SEM. These green composites have the potential to substitute PP‐based composites in some applications.

     

Thermal,Rheological, and Mechanical Behaviors of LLDPE/PEMA/Clay Nanocomposites: Effect of Interaction Between Polymer,Compatibilizer, and Nanofiller

Summary: Linear low density polyethylene/maleic anhydride grafted polyethylene/montmorillonite clay (LLDPE/PEMA/clay) nanocomposites prepared using a co‐rotating twin screw extruder exhibit unique thermal, rheological, and mechanical behaviors. All the mechanical properties including ductility increase with clay loading. X‐ray diffraction analysis and TEM images reveal an intercalated clay structure for the LLDPE/PEMA/clay composite with 5% clay and an exfoliated structure for that with 2% clay. Differential scanning calorimetry shows that the addition of PEMA does not influence the melting temperature but favors the formation of more thin lamellas. Rheological characterization indicates that the LLDPE‐PEMA blend has similar rheological behavior to neat LLDPE, implying the two polymers are completely miscible. The composites exhibit significantly higher storage and loss modulus and complex viscosity at low frequencies, and the magnitude of all these properties increases with clay loading. Furthermore, the slopes of G′, G″, and complex viscosity versus frequency are similar for the composites of different phase morphologies, suggesting that the rheological behaviors of the composites depends more on clay loading than phase morphology. The enhanced miscibility between LLDPE and PEMA, and more importantly, interfacial interaction between clay, PEMA, and LLDPE, are responsible for the distinct improvement in all the mechanical properties of the composite, and in particular for the marked improvement in ductility.

Stress‐strain diagram for LLDPE, LLDPE/PEMA, and LLDPE/PEME‐clay nanocomposites.     

High‐Performance Pristine Graphene/Epoxy Composites With Enhanced Mechanical and Electrical Properties

High‐strength conductive pristine graphene/epoxy composites are prepared by two simple processing methods – freeze dry/mixing and solution processing. PVP‐stabilized graphene is aggregation‐resistant and allows for excellent dispersion in both the resin and final composite, as confirmed by optical microscopy and SEM images. The superior dispersion quality results in excellent nanofiller/matrix load transfer, with a 38% increase in strength and a 37% improvement in modulus for 0.46 vol% graphene loading. The composites have a very low electrical percolation threshold of 0.088 vol%. Despite the effectiveness of both methods, the freeze‐drying method is more promising and versatile enough to be used for graphene dispersion in a wide range of other composite precursors.

     

A Reactive Flame Retardant as a Poly(propylene)‐Sized Glass Adhesion Promoter

Summary: Contact‐mode AFM adhesion strength measurements were employed in order to investigate the capability of PBBMA FR as an adhesion promoter in PP composites. The reactive FR exhibited superior coupling properties in comparison to conventional coupling agents such as PP‐g‐ma introduced in reinforced PP composites.

AFM image showing the recess carved out by the AFM tip in a PBBMA layer deposited on glass treated with APS.