The effects of cross-linked starch on the properties of thermoplastic starch

In order to improve the poor tensile properties and high water absorption of thermoplastic starch (TPS), cross-linked starch was added into the TPS matrix. The cross-linked starch contents ranged from 0 wt% to 20 wt%. The TPS/cross-linked starch composites were analyzed for the morphology of their fractured surfaces, the thermal decomposition temperatures, ability to absorb water and mechanical properties. The results showed that the incorporation of cross-linked starch into the TPS matrix caused considerable improvement to tensile strength. The maximum tensile strength was obtained with addition of 20 wt% cross-linked starch. Moreover, water absorption of the TPS samples was clearly reduced by the inclusion of cross-linked starch. The thermal degradation temperatures of the composites were also higher than those of the TPS matrix.     

Thermally mendable epoxy resin strengthened with carbon nanofibres

This paper investigates the strengthening and toughening effects of carbon nanofibres (CNFs) on a self-healing thermoset/thermoplastic blend, i.e. an epoxy/poly (ε-caprolactone) (PCL) blend. The self-healing material system was prepared by polymer blending that produced a co-continuous phase-separated structure. The addition of CNFs altered the phase structures, leading to smaller domain sizes or even completely altering the phase separation mechanism, e.g. conversion from a co-continuous phase-separated structure to a particulate phase structure when the CNF content reached a certain level (0.3 wt% in this work). As the content of CNFs increased, the resulting nanocomposite became stronger and tougher, but the self-healing efficiency diminished; the optimal CNF content was found to be 0.2 wt%, which produced the highest strength, toughness and hardness, while achieving around 70% of healing efficiency.     

Environmental resistance of flax/bio-based epoxy and flax/polyurethane composites manufactured by resin transfer moulding

As biocomposites are highly sensitive to water absorption, the aim of this study was to compare the physical properties two biocomposites: (1) a flax/bio-based epoxy (Entropy SUPER SAP CLR/INS) and (2) a flax/polyurethane (HENKEL LOCTITE MAX 3). Both materials were reinforced with 14 layers of flax (TEXONIC twill 2 × 2) and manufactured using a resin transfer moulding process. Post-cured composite samples were aged at 90% RH and 30 °C for various periods of time up to 720 h. The results showed that both composites followed a Fickian diffusion behaviour. Water had a plasticizing effect on the composites and it changed their failure mode. This effect took longer to appear for the polyurethane composites. The chemical bonds between the hydroxyl groups of the fibres and the isocyanate lead to a stronger interface which improved the mechanical properties (short beam and compressive strengths) as compared to the flax/bio-epoxy composites.     

Flame-retarded biocomposites of poly(lactic acid), distiller’s dried grains with solubles and resorcinol di(phenyl phosphate)

The distiller’s dried grains with solubles (DDGS) were treated by smashing and water washing processes. The treatment effects on DDGS were analyzed, and the results showed that the thermal stability and the hydrophobicity of DDGS were improved by the treatment processes. The flame retarded biocomposites of poly(lactic acid) (PLA) with DDGS and degradable polymeric flame retardant resorcinol di(phenyl phosphate) (RDP) were prepared. The prepared biocomposites had good mechanical properties and the tensile strength of the biocomposite containing 15 wt% RDP and 15 wt% DDGS reached approximately 53 MPa. Meanwhile, using the limited oxygen index (LOI) and the underwriters laboratory (UL-94) tests, for the biocomposite, the LOI value was approximately 27.5% and V-0 rating in UL-94 was attained. Furthermore, the peak heat release rate of this biocomposite was reduced to 275 kW/m² compared with 310 kW/m² for pure PLA. After burning of the biocomposites, compact and coherent charred layer was formed and the char residues were analyzed in detail.     

Processing and thermal,mechanical and morphological characterization of post-consumer polyolefins/thermoplastic starch blends

Mixtures of high density polyethylene (HDPE) and polypropylene (PP), both post-consumer polymers were blended with thermoplastic starch (TPS). Corn starch plastification was carried out by extrusion with glycerin addition. The behaviour of TPS produced was investigated in the processing and thermal, mechanical and morphology characterization of post-consumer HDPE/PP blends (100/0, 75/25, and 0/100 wt.%) in different proportions of TPS (30%, 40% and 50% wt.%) by melting flow index (MFI), tensile property measurements, and scanning electron microscopy (SEM), respectively. The addition of TPS reduced the MFI of PP and increased of HDPE and HDPE/PP blends. TPS also decreased the tensile strength and elongation at break, and increased the rigidity of the materials. SEM showed separation of phase between the poliolefins and TPS.     

Studies on the structure and properties of thermoplastic starch/luffa fiber composites

Thermoplastic starch (TPS)/luffa fiber composites were prepared using compression molding. The luffa fiber contents ranged from 0 wt.% to 20 wt.%. The tensile strength of the TPS/luffa fiber composite with 10 wt.% of luffa fiber had a twofold increase compared to TPS. The temperature values of maximum weight loss of the TPS/luffa fiber composites were higher than for TPS. The water absorption of the TPS/luffa fiber composites decreased significantly when the luffa fiber contents increased. The strength of adhesion between the luffa fiber and the TPS matrix was clearly demonstrated by their compatibility presumably due to their similar chemical structures as shown by scanning electron microscope (SEM) micrographs and Fourier transform infrared (FTIR) spectra.     

Strong and optically transparent biocomposites reinforced with cellulose nanofibers isolated from peanut shell

Cellulose nanofibers–reinforced PVA biocomposites were prepared from peanut shell by chemical–mechanical treatments and impregnation method. The composite films were optically transparent and flexible, showed high mechanical and thermal properties. FE-SEM images showed that the isolated fibrous fragments had highly uniform diameters in the range of 15–50 nm and formed fine network structure, which is a guarantee of the transparency of biocomposites. Compared to that of pure PVA resin, the modulus and tensile strength of prepared nanocomposites increased from 0.6 GPa to 6.0 GPa and from 31 MPa to 125 MPa respectively with the fiber content as high as 80 wt%, while the light transmission of the composite only decreased 7% at a 600 nm wavelength. Furthermore, the composites exhibited excellent thermal properties with CTE as low as 19.1 ppm/K. These favorable properties indicated the high reinforcing efficiency of the cellulose nanofibers isolated from peanut shell in PVA composites.     

Mixture of fuels approach for solution combustion synthesis of nanoscale MgAl2O4 powders

Nanoscale MgAl₂O₄ powders were synthesized via a microwave-assisted solution combustion process using various mixtures of urea, glycine and starch as fuel. The effects of starch addition on characteristics (e.g. specific surface area and crystallite size) of the as-resulted powders were also investigated. The experimental results revealed that the specific surface area of the powders was significantly increased as the starch content rose from 0 to 35.6 wt.%, followed by a slight decrease when it was further raised to 54.7 wt.%. The scanning electron microscope micrographs disclosed that starch addition also affected the morphology of porous nanoparticles’ agglomerates and was remarkably beneficial to dissipate the as-produced nanoparticles. Higher degree of dissipation and larger specific surface area of the powders resulted from starch addition were mainly attributed to a larger amount of gases evolved during combustion and/or lower combustion temperature.     

Poly(ε-caprolactone)-based nanocomposites: Influence of compatibilization on properties of poly(ε-caprolactone)–silica nanocomposites

In the present paper, results about preparation and characterization of poly(ε-caprolactone) (PCL) based nanocomposites filled with silica nanoparticles are reported. In order to promote polymer/inorganic nanofiller compatibility and to increase the interfacial adhesion between the two components, silica nanoparticles surface has been functionalised by grafting a M_w = 10,000 Da PCL onto it. Successively, PCL based nanocomposites have been prepared by extrusion process. The relationships among size, amount of the nanofiller, organic coating and the final properties have been investigated. The morphological analysis has revealed that the silica functionalization can provide a useful method of preparation of the nanocomposites with the achievement of a fine, a good dispersion and a strong adhesion level. Thermal characterization has shown an improved thermal stability due to the presence of the silica nanoparticles, especially in the case of modified nanofillers. Finally mechanical tests revealed an increase of the Young’s modulus in the PCL based nanocomposites.     

Structure property relation of hybrid biocomposites based on jute,viscose and polypropylene: The effect of the fibre content and the length on the fracture toughness and the fatigue properties

In the present study, the extent of jute and viscose fibre breakage during the extrusion process on the fracture toughness and the fatigue properties was investigated. The composite materials were manufactured using direct long fibre thermoplastic (D-LFT) extrusion, followed by compression moulding. The fracture toughness (K_IC) and the fracture energy (G_IC) of the PP–J30 composites were significantly improved (133% and 514%, respectively) with the addition of 10 wt% viscose fibres, indicating hindered crack propagation. The addition of viscose fibres resulted in three times higher fatigue life compared with that of the unmodified jute composites. Further, with the addition of (2 wt%) MAPP, the PP–J30–V10 resulted in a higher average viscose fibre length of 8.1 mm, and the fracture toughness and fracture energy increased from 9.1 to 10.0 MPa m^1/2 and 28.9 to 31.2 kJ/m², respectively. Similarly, the fatigue life increased 51% compared with the PP–J30–V10, thus demonstrating the increased work energy due to hindrance of the propagation of cracks.     

Effect of starch type on miscibility in poly(ethylene oxide) (PEO)/starch blends and cytotoxicity assays

This study reports results on the miscibility of polymer blends based on PEO and different starches (unmodified, cationic, and hydrophobic) and their respective cytotoxicity. Films of PEO/starch blends at different weight ratios (95/05, 90/10, 80/20, 70/30, 65/35, and 60/40), as well as films of pure PEO as control, were prepared by casting methodology. Several techniques, such as SEM, WAXS, FTIR, and FT-Raman spectroscopy were used in this study for evaluating blend miscibility. The results revealed that the miscibility of such blends is dependent on the type of starch used. Regarding the PEO/unmodified starch blends, it was concluded that the system is miscible in the ratio range from 90/10 to 65/35. Although the PEO/hydrophobic starch blends are miscible in all the studied range, blends of PEO and cationic starch are immiscible, regardless the blend ratio. The different samples presented distinct cytotoxic behaviors. PEO and hydrophobic starch presented no relevant toxicity (CC_50/72 > 2.5 mg/mL). Otherwise, the cationic starch was the most harmful for the cells. The blends presented cytotoxicity values between those of PEO and cationic starch.     

Localized toughening of carbon/epoxy laminates using dissolvable thermoplastic interleaves and electrospun fibres

Mode-I interlaminar toughness improvement through epoxy-dissolvable thermoplastic phenoxy interleaves of different surface-to-volume ratios is reported. Shear yielding around the crack tip in the reaction-induced phase separated blend morphology was found to be the main toughening mechanism responsible. The dissolution behaviour of thermoplastic phenoxy fibre within epoxy resin was studied, and a simple relationship between dissolution time, temperature, and original fibre diameter is proposed. Thermoplastic interleaves in the form of continuous films and electrospun fibre mats of equivalent weights were employed in order to study the effect of surface-to-volume ratio on dissolution and toughening behaviour. The toughness improvements obtained for the dissolvable thermoplastic nanofibre interleaves were the highest ever reported for these types of toughening concepts, with a dramatic increment from 0.56 kJ/m² to 1.90 kJ/m² with only 1.6 wt.% phenoxy interleaves. Differences in toughening behaviour between continuous films and nanofibre mats are explained in relation to differences in dissolution time.     

Starch/polylactide sustainable composites: Interface tailoring with graphene oxide

The high production cost of polylactide (PLA) can be effectively reduced by simply mixing with starch, unfortunately a trade-off of its mechanical properties. In this paper, we reported a new strategy in which graphene oxide (GO) was used as a compatibilizer to bridge PLA and starch. The native starch was first cationized and then encapsulated with GO by electrostatic force between the negatively charged GO and the positively charged cationic starch. The encapsulating GO was reduced by the quaternary ammonium ions on the cationic starch, which converted the surface of the starch from hydrophilic to hydrophobic. Due to the amphipathicity approximation between PLA and starch, a good dispersion as well as a strong interfacial adhesion was achieved. The PLA composite reinforced with GO encapsulated starch exhibited much higher yield strength than that of pure PLA, increasing from 36.64 MPa up to 41.40 MPa.     

Effect of ammonium polyphosphate on flame retardancy,thermal stability and mechanical properties of alkali treated kenaf fiber filled PLA biocomposites

In present research polylactic acid (PLA) biocomposites were prepared from PLA and kenaf fiber using dry blending, twin screw extrusion and compression molding techniques. PLA was blended with kenaf core fiber, polyethylene glycol (PEG) and ammonium polyphosphate (APP). Kenaf fiber was treated with 3%, 6% and 9% NaOH solution separately. Both raw and treated kenaf along with 10, 15 and 20 phr APP was utilized during composite preparation. The effects of APP content and alkali treatment on flammability, thermal and mechanical properties of kenaf fiber filled PLA biocomposites were investigated. APP is shown to be very effective in improving flame retardancy properties according to limiting oxygen index measurement due to increased char residue at high temperatures. However addition of APP decreased the compatibility between PLA and kenaf fiber, resulting in significant reduction of the mechanical properties of PLA biocomposites. Thermogravimetric analysis (TGA) showed that NaOH treatment improved the thermal stability of PLA biocomposites and decreased carbonaceous char formation.     

Influence of processing parameters on the impact strength of biocomposites: A statistical approach

Injection molded biocomposites from a new biodegradable polymer blend based matrix system and miscanthus natural fibers were successfully fabricated and characterized. The blend matrix, a 40:60 wt% blend of poly(butylene adipate-co-terephthalate), PBAT and poly(butylene succinate), PBS was chosen based on their required engineering properties for the targeted biocomposite uses. A big scientific challenge of biocomposites is in improving impact strength within the desired tensile and flexural properties. The stiffness–toughness balance is one of the biggest scientific hurdles in natural fiber composites. Thus, the key aspect of the present study was in investigating an in-depth statistical approach on influence of melt processing parameters on the impact strength of the biocomposite. A full factorial experimental design was used to predict the statistically significant variables on the impact strength of the PBS/PBAT/miscanthus biocomposites. Among the selected processing parameters, fiber length has a most significant effect on the impact strength of the biocomposites.     

Cork–polymer biocomposites: Mechanical,structural and thermal properties

This work addresses to the preparation of biocomposites resulting from the combination of different biodegradable aliphatic polyesters with cork (30 wt.%). The lignocellulosic biomass with closed cellular structure was compounded with poly(L-lactic acid) (PLLA), polyhydroxybutyrate-co-hydroxyvalerate (PHBV), poly-ε-caprolactone (PCL) and starch-poly-ε-caprolactone (SPCL) blend using a twin-screw extruder prior to injection moulding into tensile samples. The physico-mechanical and thermal properties of the matrices and the bio-based cork composites were investigated. This study shows that the addition of cork contributes to produce lightweight materials using PLLA and PHBV matrices and promotes an increase on the stiffness of PCL. The fracture morphology observations showed good physical cork–matrix bonding with absence of voids or cavities between cork and the bio-based polyesters. Cork increases the crystallinity degree of the biocomposites. These findings suggest that the cork–polymer biocomposites are a viable alternative to develop more sustainable composite materials, such as automotive interior parts and bio-based caps for wine bottles as it has been shown as proof-of-concept.     

Innovative flax tapes reinforced Acrodur biocomposites: A new alternative for automotive applications

Flax Acrodur biocomposites are elaborated with an innovative flax reinforcement consisting of long technical fibers unidirectionally arranged without any weft and twist. The fibers cohesion is performed by using a new process consisting by reactivating the pectin cement. A polyester thermoset matrix (Acrodur) is used to impregnate the flax reinforcement and to produce unidirectional (UD) laminates. The relationship between the main process variables (drying, fibers content, densification and curing parameters) and the properties of the biocomposites is investigated. The optimized biocomposites have an elastic modulus of 18 ± 1 GPa with 55% wt.% flax fiber content and a low density of 0.93 g/cm³. The thermal stability of the developed biocomposites is also investigated by Differential Scanning Calorimetry (DSC), Thermogravimetric Analysis (TGA) and Dynamic Mechanical Analysis (DMA). DMA results show a slight change of the storage modulus in a range of temperature from 23 °C to 160 °C. The appropriate processing parameters for the biocomposites are established. The developed flax tapes reinforced Acrodur biocomposites have a potential to be integrated for automotive applications thanks to their high stiffness/weight ratio and environmental advantages.     

Development of crayfish protein-PCL biocomposite material processed by injection moulding

A combination of crayfish flour (CF, with 60% protein) and Polycaprolactone (PCL) was successfully used to prepare biocomposites by a process that consists of two stages: mixing with glycerol (GL) as plasticizer and injection moulding of CF/GL/PCL blends. Mixing rheometry and Differential Scanning Calorimetry (DSC) measurements were found to be useful to select suitable injection moulding conditions. A remarkable enhancement in mechanical properties was found for PCL containing systems, even when crystalline structure remains unaltered. PCL yields a dominant contribution to the elastic response and confer a higher ability to absorb energy before rupture, but also the protein/plasticiser ratio must be considered.     

Modeling of hydrothermal aging of short flax fiber reinforced composites

As a contribution to the prediction of the evolutionary behavior of biocomposites in service conditions, this study focused on the simulation of the hydrothermal aging of short natural fiber reinforced composites made by extrusion/injection molding. We endeavored to model the reversible modifications of the behavior of PLA and PLA/flax composites when immersed in water at different temperatures (20, 35 and 50 °C). A numerical model accounting for the heterogeneous mechanisms involved during aging such as water diffusion and the resulting swelling and plasticizing of polymers was implemented. Simulated data proved to be in perfect accordance with experimental results as long as no irreversible mechanism was occurring. The deviations of the simulated data from experimental results were limited at 35 °C but significant at 50 °C. Finally, the influence of moisture on the local elastic modulus of flax fibers was inferred thanks to the Halpin-Kardos homogenization model.     

Dramatic mechanical and thermal increments of thermoplastic composites by multi-scale synergetic reinforcement: Carbon fiber and graphene nanoplatelet

We report an easy and efficient approach to the development of advanced thermoplastic composites based on multi-scale carbon fiber (CF) and graphene nanoplatelet (GN) reinforcement. Poly (arylene ether nitrile) (PEN)/CF/GN composites, prepared by the twin-screw extrusion, exhibited excellent mechanical properties. For example, the flexural modulus of PEN/CF/GN composites was 18.6 GPa, which is 1.7, 4.5 and 6.4 times larger than those of PEN/CF composites, PEN/GN composites and PEN host, respectively. Based on the SEM image observation, such mechanical enhancements can be attributed to the synergetic effect of micro-scale CF and nano-scale GN in the PEN matrix (decreased matrix-rich and free-volume regions and enhanced interfacial interactions). For 5 wt.% GN-filled PEN/CF/GN composites, the T_d30% of PEN/CF/GN composites was 145 °C and 62.8 °C compared with those of PEN host and PEN/CF composites, respectively. This study has demonstrated that multi-scale CF and GN have an obvious synergetic reinforcing effect on the mechanical properties and thermal stabilities of thermoplastic composites, which provides an easy and effective way to design and improve the properties of composite materials.