Effect of processing conditions on mechanical and viscoelastic properties of biocomposites

To study the effects of processing conditions on the viscoelastic and mechanical properties of biodegradable composites, we prepared several composites based on sisal fibers and biodegradable polymers. The effects of processing conditions such as the speed of rotation, temperature, and time of mixing were investigated. The mechanical and viscoelastic properties of these composites were affected by the processing conditions. This was principally due to the modification of the initial aspect ratio of the natural fibers as a result of the shear stresses that developed in the mixer during the compounding. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 1637–1642, 2003     

Effects of poly(dimethyl siloxane) on the water absorption and natural degradation of poly(lactic acid)/oil‐palm empty‐fruit‐bunch fiber biocomposites

Composites were fabricated with poly(lactic acid) and oil‐palm empty‐fruit‐bunch (EFB) fibers with extrusion; this was followed by an injection‐molding technique. Before compounding, the surface of the fiber was modified through ultrasound and poly(dimethyl siloxane) (PDMS). The influences of the ultrasound and PDMS on the water absorption and biodegradability of the composites were investigated. Additionally, the composites were buried under soil for 6 months, and their biodegradability was assessed through different characterization techniques, such as tensile testing and weight loss and diffussability measurement. The changes on the surface of the fibers due to treatment were examined by scanning electron microscopy analysis, and the influences on the biodegradability of the composites were observed. Functional group analysis and possible changes before and after degradation were also examined by a Fourier transform infrared spectrophotometric technique. The results analyses revealed that the treatment of fibers improved the density of the fibers and reduced the water uptake of the composites. The overall weight loss due to soil burial testing was found to be maximum for the untreated‐fiber‐based composites (6.8%), whereas the ultrasound‐ and silane‐treated composites showed the minimum value of weight loss (3.7%). The deterioration of the tensile strength due to degradation was found to be at a maximum for the untreated‐fiber‐based composite (27%), whereas the ultrasound‐ and silane‐treated‐fiber‐based composites showed a minimum value of 8%. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42784.     

Biodegradable composites: Morphological,chemical, thermal,and mechanical properties of composites of poly(hydroxybutyrate‐co‐hydroxyvalerate) with curaua fibers after exposure to simulated soil

Composites produced from biodegradable polymeric matrixes reinforced with vegetable fibers have attractive mechanical properties and are environmentally friendly. This work is directed to the biodegradation of a composite made of a poly(hydroxybutyrate‐co‐hydroxyvalerate) matrix reinforced with curaua fibers (with and without alkaline treatment) in simulated soil. The composites were developed by extrusion and injection and were later buried in simulated soil according to the ASTM G160‐03 method. Scanning electron microscopy showed evidence of microbial attack on the samples surfaces. Infrared spectra showed that the composites biodegradation was mainly caused by erosion of the surface layer resulting from microorganisms activity. Thermogravimetric analysis pointed out reduced thermal stability of the samples, and results of differential scanning calorimetry showed that the degree of crystallinity increases and then decreases progressively throughout the degradation period, indicating that enzymatic degradation primarily occurs in the amorphous phase material and thereafter in the crystalline phase. For curaua composite fibers, reductions in tensile strength and elastic modulus are more significant, indicating that the presence of fibers promotes biodegradation of the curaua fiber. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40712.     

Hybrid biocomposites with enhanced thermal and mechanical properties for structural applications

The current work focuses on enhancing the mechanical and thermal properties of sisal fiber reinforced composites that were previously used in developing interior automotive trims. In order to extend their use in other structural applications, two hybrid biocomposites with the combination of sisal (SF) and glass fiber (GF)‐SF20/GF10 and SF10/GF20 were blended with polypropylene via extrusion and injection molding process. Critical material properties such as density, fogging, acoustic, mechanical, thermal, and rheological properties were evaluated and results were analyzed using ANOVA. Hybridization of SF and GF enhanced flexural strength and thermal properties of the biocomposites by 33 and 19%, respectively, while no significant change in acoustic, impact and rheological properties were observed. The properties of the hybrid biocomposites were compared with the material specification of a battery tray and it was found that these hybrid biocomposites could be better alternative materials in structural applications. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42452.     

Effect of geometry and loading fractions on energy absorbing properties of fiberglass polymer composite under quasi‐static and low‐velocity impact loadings

The focus of this study is to experimentally investigate the mechanical properties of fiberglass reinforced composite with various aspect ratios and loading fractions in the quasi‐static and low‐velocity impact loading conditions. In this study, short fiberglass reinforced polycarbonate composite materials were fabricated via a solution mixing method and characterized for their tensile properties by varying both fiberglass loading fraction and aspect ratio. The tensile properties including tensile toughness of the fiberglass reinforced composites were characterized and compared. It was observed in this study that the toughness of the composite was dramatically improved whereas the tensile strength and Young's modulus were moderately enhanced over the neat polymer, which were measured to be only up to 15% and 70% increase, respectively. The low‐velocity impact behaviors of the fiberglass composites were also investigated and compared to the tensile toughness of the corresponding composites. Besides, the effect of thickness on their low‐velocity impact properties was investigated. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40821.     

Effects of the moisture and fiber content on the mechanical properties of biodegradable polymer–sisal fiber biocomposites

The matrix of the composites that were used in this work was a commercial blend based on starch and cellulose derivatives. The biodegradable polymer was reinforced by short‐sisal fibers with a range in fiber content of 5–15 wt %. The effects of humidity on the diffusion coefficients, equilibrium moisture content, and mechanical properties were studied. Equations obtained from microscopic mass balances for diffusion in solids were used to predict the absorbed humidity in both components (the sisal fibers and biodegradable polymer) and in the composites as a function of time. Different model predictions of the composite diffusion coefficients as a function of the filler concentration were also examined, and they were found to be in agreement with the experimental results. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 91: 4007–4016, 2004     

Effects of wheat straw fiber content and characteristics,and coupling agent concentration on the mechanical properties of wheat straw fiber‐polypropylene composites

Wheat straw fiber‐polypropylene (PP) composites were prepared to investigate the effects of wheat straw fiber content (10, 20, 30, 40, and 50 wt %), fiber size (9, 28, and 35 mesh), and maleic anhydride grafted polypropylene (MAPP) concentration (1, 2, 5, and 10 wt %) on the static and dynamic mechanical properties of the wheat straw fiber‐PP composites in this study. The tensile modulus and strength of the composites increased linearly with increasing wheat straw fiber content up to 40%, whereas the elongation at break decreased dramatically to 3.78%. Compared with the composites made of the longer wheat straw fiber, the composites made of the fines (>35 mesh) had a slightly higher tensile strength of 31.2 MPa and tensile elongation of 5.39% at break. With increasing MAPP concentration, the composites showed an increase in tensile strength, and the highest tensile strength of 34.0 MPa occurred when the MAPP concentration reached 10 wt %. As wheat straw fiber content increased from 0 to 40%, the flexural modulus of the composites increased gradually from 1335 to 3437 MPa. The MAPP concentration and wheat straw fiber size distribution had no appreciable effect on the static flexural modulus of the composites. The storage flexural modulus of the composites increased with increasing wheat straw fiber content. The scanning electron microscopy (SEM) observation on the fracture surface of the composites indicated that a high wheat straw fiber content (>30 wt %) resulted in fiber agglomeration and a reduction in interfacial bonding strength. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Modification of dry‐spun Suplon polyimide fibers by mixed‐acid oxidation and their effects on the properties of polypropylene‐resin‐based composites

In this study, the effects of mixed‐acid oxidation on the contents of surface elements, morphology, fiber fineness, mechanical properties, mass change rate, chemical structure, and microaggregate structure of dry‐spun Suplon polyimide (PI) fibers were systematically investigated with wet chemical treatment with HNO₃/H₂SO₄. Experiments investigating both the improvement in the O/C ratio of the fiber surface elements and the changes in other performance features were conducted through the functional modification of the fibers. Meanwhile, the causes of specific changes in the mechanical properties of the oxidized PI‐fiber‐reinforced polypropylene‐resin‐based composites were studied and are discussed. The results of this study demonstrate that the treatment of the fibers with HNO₃/H₂SO₄ mixed‐acid oxidation resulted in significant changes in the properties of the fibers; these changes included an uneven surface, increased specific surface area and surface roughness, a locally etched surface, increased surface energy and O/C ratio, an enhanced wettability, an increased fiber fineness, reduced mechanical properties, and a mass gain in the fibers. Although the chemical structures of the fibers treated by oxidized HNO₃/H₂SO₄ were not significantly changed compared to those of the untreated fibers, the microscopic aggregation of the treated fibers changed to some degree, and the ratio of the amorphous regions significantly increased. Taken together, the functional modification of the PI fiber surface was achieved efficiently through the use of a suitable HNO₃/H₂SO₄ oxidation process and with other performance features of the fibers taken into account. This was favorable for the enhancement of the interfacial properties of the polypropylene fibers and the matrix resins, and thus, the modification improved the mechanical properties of the composites. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44932.     

Mechanical and biodegradation properties of bamboo fiber-reinforced starch/polypropylene biodegradable composites

Bamboo fiber (BF)-reinforced starch/polypropylene (PP) composites were prepared by extrusion and injection molding methods. The mechanical and thermal properties and water absorption were evaluated by different methods. Moreover, composite samples were subjected to biodegradation through soil burial test and microbes medium degradation. Different stages of biodegradation were investigated by weight loss, attenuated total reflection Fourier transformed infrared spectroscopy, differential scanning calorimeter, and scanning electron microscope. It was found that contents of BF and starch resin had a significant influence on the properties of the composites. With more content of BF, the composite exhibited a better flexural property and biodegradation. A distinct decrease of weight loss and mechanical properties indicated the degradation caused by the microbes. After biodegradation, thermal stability of the composites decreased while the crystallinity of PP increased. The results prove that the composites more easily tend to be degraded and assimilated by microbes. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 137, 48694.     

Improvement of mechanical properties of natural fiber–polypropylene composites using successive alkaline treatments

The use of natural fibers (NFs) in polymer composites for structural applications has increased greatly in the last years, owing to their abundance and biodegradability. In this work, an innovative and simple successive alkali treatment has been developed to improve the mechanical properties of NFs/polypropylene (PP) composites. Three different cellulosic fibers (curauá, jute, and flax) were used, with a fixed proportion of 10 wt %. The fibers were immersed several times in a 5 wt % NaOH solution. Thermogravimetric analysis data showed an improvement in thermal properties of the fibers, as well as the increase of the crystallinity degree was measured by X‐ray diffraction. By Fourier transform infrared spectroscopy, disappearance of characteristics peaks of hemicelluloses and lignin was observed. Finally, mechanical behavior of the NF/PP composites was examined, using dynamic mechanical analysis. The results revealed that the curauá/PP mechanical properties were significantly improved, showing the positive effect of the successive alkali treatments. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41710.     

Biocomposites based on poly(lactic acid) and seaweed wastes from agar extraction: Evaluation of physicochemical properties

Seaweed waste (SWW) is a residue or by‐product from the filtration step of the agar extraction process, and it has been explored as an inexpensive and effective filler for incorporation by melt blending into a poly(lactic acid) (PLA) matrix. PLA‐SWW biocomposites were manufactured with various contents of SWW (0, 5, 10, 15, and 20 wt %) using a sheet extrusion process. PLA was functionalized with maleic anhydride (MAH) by reactive extrusion using dicumyl peroxide (DCP) as an initiator, and it was extruded using 0, 5, and 20 wt %. SWW content. The mechanical, thermal, structural, and morphological properties of the processed biocomposites were investigated. Regarding the mechanical behavior, a slight increase in the tensile modulus was observed at low SWW content. The thermal properties indicated that the rigid amorphous phase content was enhanced in the biocomposites. This work suggests that SWW can be used as filler to develop environmental friendly biocomposites. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42320.     

Studies on the effect of silicon carbide nanoparticles on the thermal,mechanical, and biodegradation properties of poly(caprolactone)

In this work, silicon carbide (SiC) nanoparticles were used to reinforce polycaprolactone (PCL). The nanocomposites were prepared by melt‐mixing followed by mould extrusion. The effect of increased SiC loading on the thermal, mechanical, and dynamic mechanical properties was investigated using differential scanning calorimetry, tensile testing, and dynamic mechanical analysis (DMA), respectively. The morphology and chemical interactions were carried out by scanning electron microscopy and Fourier transform infrared spectroscopy (FTIR), respectively. The SiC nanoparticles were fairly well dispersed in the PCL matrix. FTIR indicated that there was no chemical interaction between PCL and SiC. The presence of SiC nanoparticles influenced the crystallization behavior of PCL, whereas there was no significant influence on thermal degradation behavior of PCL. Generally, the mechanical properties of the nanocomposite increased with an increase in nanoparticle content. The DMA results showed that the presence of SiC improved the storage modulus of PCL especially at higher SiC loading. Thermogravimetric analysis showed a very small influence of SiC on the thermal stability of PCL. Moreover, the glass transition temperature (T_g) of the nanocomposites shifted to lower temperatures compared to that of neat PCL. The crystal structure was not significantly influenced by the presence of SiC. The biodegradation process of PCL in soil environment delayed in the presence of SiC. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42145.     

Kenaf‐bast‐fiber‐filled biodegradable poly(butylene succinate) composites: Effects of fiber loading,fiber length,and maleated poly(butylene succinate) on the flexural and impact properties

Poly(butylene succinate) (PBS) filled kenaf bast fiber (KBF) composites were fabricated via compression molding. The effects of KBF loading on the flexural and impact properties of the composites were investigated for fiber loadings of 10–40 wt %. The optimum flexural strength of the composites was achieved at 30 wt % fiber loading. However, the flexural modulus of the composites kept increasing with increasing fiber loading. Increasing the fiber loading led to a drop in the impact strength of about 57.5–73.6%; this was due to the stiff nature of the KBF. The effect of the fiber length (5, 10, 15, and 20 mm) on the flexural and impact properties was investigated for the 30 wt % KBF loaded composites. The composites with 10‐mm KBF showed the highest flexural and impact properties in comparison to the others. The inferior flexural and impact strength of the composites with 15‐ and 20‐mm KBF could be attributed to the relatively longer fibers that underwent fiber attrition during compounding, which consequently led to the deterioration of the fiber. This was proven by analyses of the fiber length, diameter, and aspect ratio. The addition of maleated PBS as a compatibilizer resulted in the enhancement of the composite's flexural and impact properties due to the formation of better fiber–matrix interfacial adhesion. This was proven by scanning electron microscopy observations of the composites' fracture surfaces. The removal of unreacted maleic anhydride and dicumyl peroxide residuals from the compatibilizers led to better fiber–matrix interfacial adhesion and a slightly enhanced composite strength. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

The effect of multiscale hybridization on the mechanical properties of natural fiber-reinforced composites

The main objective of this work was to investigate the effect of reinforcements at different scales on the mechanical properties of natural fiber-reinforced composites. Pure jute and interlaminar hybrid jute/glass fiber-reinforced polymer composites were fabricated. Different types of fillers in two weight fractions (1 and 3 wt. %) were used as second reinforcements in the hybrid jute/glass composites. Tensile, flexural, and impact tests were performed. It was found that the macroscale inter-play hybridization significantly improved the mechanical properties of the pure jute fiber based composites. When the fillers are used as second hybridization, the modified composites presented higher mechanical properties when compared to pure jute composites. However, the effect of fillers on the mechanical properties of the hybrid composites presented various trends due to the interaction between several factors (i.e., particle scale, content, and nature), which cannot always be separated. Increasing the synthetic filler content improved the tensile properties of the filled hybrid composites, while increasing the natural filler content worsen the tensile properties. The flexural strength of the multiscale hybrid composites was improved, while the impact properties were negatively affected.     

Antimicrobial carbon materials incorporating copper nano‐crystallites and their PLA composites

In the first stage, carbon materials were manufactured from chitin and chitosan as the main precursor. Chitin and chitosan were impregnated with Cu²⁺ ions. Using heat treatment, the organic matter (biopolymers) was transformed into a porous carbon matrix, while copper ions were transformed into copper‐based nano‐crystallites containing copper atoms in a +1 and 0 oxidation state. Such synthesized carbons exhibited high contact antifungal activity, e.g., for sample, CH‐ACu0.1_Ox against R. nigricans the inhibition zone is 10.27 mm. In the second stage, composite polymer films were manufactured by mixing polylactide (PLA) and the obtained microbial carbon material (up to 3 wt % Cu‐carbon content). Despite the very low content of carbon material (3 wt %), the composite PLA films exhibited excellent microbial properties for selected bacteria and fungi, e.g., sample CuCM3%/PLA demonstrated high log₁₀ reduction values of 2.17 and 2.66 for the strains of E. coli and S. aureus, respectively. The composite films, and their components, were examined by means of diversified physicochemical methods like low temperature adsorption of nitrogen, SEM, elemental analysis, XRD, cyclic voltammetry, antifungal, and antibacterial analysis. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43429.     

Mechanical properties and biodegradability of green composites based on biodegradable polyesters and lyocell fabric

Green composites composed of regenerated cellulose (lyocell) fabric and biodegradable polyesters [poly(3‐hydroxybutyrate‐co‐3‐hydroxyvarelate) (PHBV), poly(butylene succinate) (PBS), and poly(lactic acid) (PLA)] were prepared by compression‐molding method. The tensile moduli and strength of all the biodegradable polyester/lyocell composites increased with increasing fiber content. When the obtained PLA/lyocell composites were annealed at 100°C for 3 h, the tensile strength and moduli were lowered despite the increase of degree of crystallization of the PLA component. The SEM observation of the composites revealed that the surface of the annealed composite has many cracks caused by the shrinkage of the PLA adhered to lyocell fabric. Multilayered PLA/lyocell laminate composites showed considerably higher Izod impact strength than PLA. As a result of the soil viral test, although the order of higher weight loss for the single substance was lyocell > PHBV > PBS > PLA, the biodegradability of the green composites did not reflect the order of a single substance because of the structural defect of the composite. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 3857–3863, 2004     

Determination of mass transport properties in food/packaging systems by local measurement with Raman microspectroscopy

A fast, nondestructive method based on the determination of local concentration profiles in the polymer thickness with Raman microspectroscopy is presented here. It was used to assess the diffusivity of a model molecule (p‐terphenyl) in amorphous polystyrene films at 95°C (2.38 ± 1.08 × 10^?17 m²/s). This methodology was validated by comparison with a more classical destructive approach based on the monitoring of the concentration evolution in the whole of the film with gas chromatography (89.4 × 10^?17 m²/s). These values were in agreement with data available in the literature for molecules of the same molecular weight and temperature range determined with local measurement and were significantly lower than those determined by global measurement. Raman microspectroscopy was found to be adapted to slow diffusion speeds typically found in high‐barrier polymers; this allowed diffusivity to be obtained long before the equilibrium was reached and, thus, without the need for the partition coefficient. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40958.     

Effect of polyethylene glycol on mechanical properties of bamboo fiber-reinforced polylactic acid composites

The bamboo fiber (BF)-reinforced polylactic acid (PLA) composites were prepared using the twin-screw extruder and injection molding. Thermal gravimetric analyzer results indicated the thermal stability of BF/PLA composites decreased with increasing BF content. Differential scanning calorimeter and X-ray diffraction curves showed that BF played a role as a nucleating agent, but the crystallinity of composite materials decreased with the increasing BF content. The melt flow rate of composites reduced with the increase in BF content, resulting in a poorer processing property. The processability of the composites was improved with the addition of high molecular polyethylene glycol (PEG). Mechanics performance test showed that tensile strength and bending strength of composites increased at low loading with the BF content increased then decreased when the loading continued to increase. The tensile strength of the composite materials reached 65.46 MPa when alkali-treated BF (ABF) content was 20 wt %. The flexural strength of the composites reached 97.94 MPa when ABF content was 10 wt %. Impact performance has also been improved. PEG-20000 was the best plasticizer among the PEG-6000,PEG-10000, and PEG-20000. When the component of PEG was 10 wt %, the elongation increased by 56%. The scanning electron microscopy (SEM) result showed that the fracture of the composites was smooth, most ABF were wrapped in matrix and distribution of ABF in PLA matrix was more uniform. It means that interfacial compatibility of bamboo fiber and PLA improved after BF modified by alkali. High molecular weight PEG enhance melt flow ability of polymer, result in fibers were further enclosed in the PLA matrix and increase properties of composites. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47709.     

Preparation and properties of carbon fiber/ hydroxyapatite‐poly(methyl methacrylate) biocomposites

An in situ polymerization with a later solution co‐mixing approach was used in the preparation of polymethyl methacrylate (PMMA) matrix composites using hydroxyapatite (HA) nanoparticles and short carbon fibers(C_(f)) as reinforcing materials. The microstructures and fracture surface morphologies of the prepared C_(f)/HA‐PMMA composite were characterized using XRD, FTIR, SEM, EDS, and FESEM analyses. The mechanical properties of the composites were tested by a universal testing machine. Results show that the surface of nitric acid‐oxidized carbon fibers and lecithin‐treated HA contain new functional groups. Uniform dispersion of short fibers and HA nanoparticles in PMMA matrix is successfully achieved and the mechanical properties of the composites are obviously improved. The flexural strength, flexural modulus, and Young's modulus of the composites reach the maximum value 128.12 MPa, 1.150 GPa, and 4.572 GPa when carbon fiber and HA mass fraction arrive to 4% and 8%, respectively. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Atmospheric pressure plasma jet treatment of wheat straw for improved compatibility in epoxy composites

The aim of this study was to investigate the effects of an atmospheric‐pressure gas plasma jet treatment on the interior and exterior surface characteristics of wheat straw and on the mechanical properties of epoxy composites reinforced with wheat straw. Dry air was used as the process gas in the plasma system. A distance between the nozzle and the substrate surface (DNSS) of 35 mm was determined as the most effective parameter enabling remarkable decreases in the (surface energy) values of both the interior and exterior surfaces of virgin wheat straw. Increased intensities of the peaks related to carbon‐rich species and 11% to 43% decreases in the oxygen/carbon ratios on the surfaces confirmed the more hydrophobic nature of the plasma‐treated wheat straw. A further increase in the DNSS decreased the effectiveness of the plasma treatment, while a decrease in the DNSS caused an inverse effect on the value, probably due to the etching effect of the plasma action, which was supported by the atomic force microscopy analysis. The overall results indicated that the increased hydrophobicity and valley‐like occurrences without sharp pits created by the plasma action improved the compatibility of the wheat straw with the epoxy matrix, which contributed to superior mechanical properties of the composites. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45828.