Mechanical and viscoelastic properties of polyethylene-based microfibrillated composites from 100% recycled resources

In this study, recycled polyethylene (rPE) based microfibrillated composites (MFCs) were developed while incorporating recycled poly(ethylene terephthalate) (rPET) and recycled polyamide 6 (rPA) as the reinforcing fibrillar phases at a given weight ratio of 80 wt% (rPE)/20 wt% (rPET or rPA). The blends were first melt processed using a twin-screw extruder. The extrudates were then cold stretched at a drawing ratio of 2.5 to form rPET and rPA fibrillar structures. Next, the pelletized drawn samples were injection molded at the barrel temperatures below the melting temperatures of rPET and rPA. The tensile, three-point bending, impact strength, dynamic thermomechanical, and rheological properties of the fabricated MFCs were analyzed. The effects of injection molding barrel temperature (i.e., 150°C and 190°C) and extrusion melt processing temperature (i.e., 250°C and 275°C) on the generated fibrillar structure and the resultant properties were explored. A strong correlation between the fibrillar morphology and the mechanical properties with the extrusion and injection molding temperatures was observed. Moreover, the ethylene/n-butyl acrylate/glycidyl methacrylate (EnBAGMA) terpolymer and maleic anhydride grafted PE (MAH-g-PE) were, respectively, melt processed with rPE/rPET and rPE/rPA6 blends as compatibilizers. The compatibilizers refined the fibrillar structure and remarkably influenced mechanical properties, specifically the impact strength.     

Effect of water absorption,freezing and thawing,and photo‐aging on flexural properties of extruded HDPE/rice husk composites

Durability of lingo‐cellulosic fiber composites under environmental conditions such as moisture, freezing and thawing, and UV exposure needs to be determined prior to the use of these composite materials in outdoor applications. Dimensional stability and changes in the flexural strength and stiffness of extruded rice husk filled high‐density polyethylene composites with and without processing additives such as compatibilizers and processing aid were examined after exposing the composites to water, conditions of freeze–thaw cycles, and UV light. Water absorption results indicated a decrease in the rate of penetration of water in the composites in the presence of compatibilizers. The reduction in strength and stiffness after water absorption was lower for composites with compatibilizers than for the composites without any additives. Freezing and thawing experiments also showed the dimensional changes and degradation of strength and stiffness were less in composites with compatibilizers. Presence of processing aid in the composite showed a similar or enhanced water absorption and loss of mechanical properties, compared with those of the composite without processing additives. Although the composites showed a discoloration of the surface after the UV exposure time (745 h) studied, it was found that within this period of UV exposure the flexural strength and stiffness of the composites did not show significant change. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 3619–3625, 2006     

Optimal formulation of rice husk reinforced polyethylene composites for mechanical performance: A mixture design approach

Rice husk (RH) and linear medium density polyethylene (LMDPE) were used along with maleic anhydride grafted polyethylene (MAPE) to study the effects of component composition on the mechanical properties of the composites. Ten different blends along with four replicated blends were prepared with different selected percentages of RH, MAPE and LMDPE using mixture design approach. Trace and contour plots were used to examine the effects of RH, MAPE and LMDPE on the mechanical properties of the manufactured composites. Regression coefficients were also estimated for each fitted response (mechanical property). The results show that tensile and flexural properties of the composites improved with an increase in amount of RH, whereas Charpy impact strength decreased with increasing fibre loading. Tensile strength, flexural strength and Charpy impact strength increased with an increase in MAPE loading up to a certain percentage of MAPE, beyond which any further increase decreased these properties. The effect of MAPE on tensile and flexural modulus was not significant. The fitted models were used to optimise formulation of RH, MAPE and LMDPE for multiple responses for overall “best” mechanical properties. The optimal formulation for the overall “best” mechanical properties were found to be 50 wt% for RH, 4.1 wt% for MAPE and 45.9 wt% for LMDPE. The mechanical properties of the composite manufactured with this formulation closely matched the values predicted by the models. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40647.     

Simultaneous impact modified and chain extended glass fiber reinforced poly(lactic acid) composites: Mechanical,thermal, crystallization,and dynamic mechanical performance

Herein, glass fiber (GF) reinforced binary, ternary, and quaternary poly(lactic acid) (PLA) composites were prepared. Toughening, and chain extension of PLA was achieved through the incorporation of impact modifier and chain extender and their concurrent effects on the spectroscopic, crystallization, mechanical, thermal, and thermomechanical properties of the composites were investigated. High mechanical properties of GF influenced the mechanical performance of the composites. However, GF alone could not restrict the chain mobility of PLA due to poor interface and low crystallization activities in the PLA-GF composite. Incorporation of impact modifier and chain extender produced significantly enhanced interaction between GF and PLA. Significantly, the crystallinity, impact strength, and flexural modulus of PLA in the quaternary composite were increased by 58%, 63%, and 66%, respectively. In addition, damping and effectiveness coefficient of the PLA-GF composite were notably reduced by the simultaneous impact modification and chain extension of the reinforced composites.     

Polyvinyl chloride composites filled with olive stone flour: Mechanical,thermal, and water absorption properties

The production of olive oil leads to considerable amounts of solid waste mainly composed of hard woody endocarp called olive stones. The aim of this work is to explore the possible use of ground olive stones as fillers for polyvinyl chloride (PVC), to elaborate a cost‐effective composite material with a solid loading of up to 50 wt %. After grinding, the ensuing olive stone flour (OSF) was incorporated into a PVC matrix via melt compounding and injection molding to elaborate PVC‐OSF‐based composites with a filler content up to 50 wt %. The evolution of the mechanical performance, the impact property, the water absorbance, and wear resistance behavior, according to the OSF content, were investigated. The addition of OSF was shown to enhance the stiffness of the matrix, but at the expense of its mechanical strength. However, the strength of the composite did not fall as low as 30 MPa, and therefore, meets the requirements for many applications in plastic‐based materials. The thermal properties of the ensuing composites were also studied by thermogravimetric analysis. The results show that the addition of OSF may be effective in increasing the stiffness of the PVC‐based composite and in reducing the solid residue in the olive oil industry production. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 41083.     

Effect of fiber/matrix chemical modification on the mechanical properties and water absorption of extruded flax/polypropylene composite

Compound of flax/polypropylene (PP) is characterized concerning the mechanical properties of stiffness, strength, and impact in addition to the water absorption behavior. Manufacturing takes place by twin‐screw extruder. The extruder screw layout is modified through different kneading elements to get high fiber aspect ratio. Sodium hydroxide solution was used as a washing solution for the flax fibers' surfaces. Both fiber and matrix are chemically modified. Selected groups of the fibers were further treated using trimethoxyvinylsilan TMVS and acrylic acid AA. The PP matrix is also treated with different coupling agents; namely, maleated PP MAPP, TMVS‐MAPP, and acrylic acid‐functionalized PP AAPP. The combinations of different fiber/matrix are extruder compounded, injection molded, and finally tested. Fiber modification seems to be positive with AA‐modified surface. AAPP matrix modification improves the stiffness four times that of the untreated flax/PP. Till 30 and 40 wt %, the more the fiber is the more the strength and stiffness, respectively. MAPP‐modified matrix improves the mechanical properties and keeps low water absorption values. AAPP‐modified matrix shows the best stiffness values. TMVS‐MAPP does not seem to have distinguished improvement compared with MAPP. NaOH‐TMVS/MAPP and NaOH‐TMVS/AAPP systems can serve as alternatives to the normal NaOH/MAPP treatment. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Investigation on pull-out behavior and interface critical parameters of polymer fibers embedded in concrete and their correlation with particular fiber properties

A crucial problem in concrete engineering is the corrosion of steel reinforcements. Polymer fibers as alternative reinforcement material can prevent corrosion; however, high adhesion to concrete and good fiber mechanics are necessary for polymers to be considered as an alternative reinforcement. This study tested different thermoplastic polymer materials to evaluate their level of adhesion to concrete. The adhesion properties of different self-drawn polymer fibers were analyzed by extracting the fibers from concrete using single fiber pull-out test (SFPT). To determine the adhesion mechanism, different polymer properties were analyzed and correlated to SFPT. Strong evidence was found that the fibers mechanical properties correlate with SFPT. Roughening the fiber surface increases the SFPT results significantly. While highly polar materials can support the adhesion process, a clear correlation could not be found. This study identifies high stiffness and roughness as the crucial properties of polymer fibers used in concrete engineering. If these factors can be engineered into the fiber, polymer fibers can present an alternative to steel in concrete reinforcement.     

Green and self-lubricating polyoxymethylene composites filled with low-density polyethylene and rice husk flour

Polyoxymethylene (POM) composites filled with low-density polyethylene (LDPE) and rice husk flour (RHF) were prepared by injection molding. The POM/5 wt % LDPE/7.5 wt % RHF composite exhibited the lowest wear rate, whereas the coefficient of friction remained low, and the POM/5 wt % LDPE/5 wt % RHF composite had the best mechanical properties. X-ray diffraction analysis was carried out, and the worn surfaces were examined with scanning electron microscopy. The results showed that the addition of the filler reduced the crystallinity degree of the POM composites. The main wear mechanism for unfilled POM was adhesion, whereas for the POM composites, wear seemed to occur mainly by fatigue and abrasion. It was experimentally confirmed that the POM composite filled with LDPE and RHF, which is well-performing, low-cost, and environmentally friendly, could be a potential material for tribological applications. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

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.     

Effect of different surface treatments on polypropylene composites reinforced with yerba mate fibers: Physical,mechanical, chemical,and morphological properties

This study presents the preparation of post-consumer polypropylene (r-PP) composites filled with 30 wt% yerba mate (YM) stick particles. To improve the fiber–matrix adhesion, three surface treatments were performed: alkaline treatment with sodium hydroxide (NaOH) and use of 3-aminopropyltriethoxysilane (APTS) and maleic anhydride graft polypropylene copolymer (PP-g-MA) as coupling agents. Mechanical properties including tensile, flexural, and impact resistance were determined, and chemical (Fourier transform infrared spectroscopy [FTIR]), physical (water absorption), and morphological analyses were performed. The main findings show that the treatments were efficient in improving the mechanical properties of the composites, with emphasis on the r-PP/YM30/APTS and r-PP/YM30/PP-g-MA composites, which proved to be superior in tensile, flexion and impact strength and absorption of water compared to the untreated composite. The morphological analysis showed a better interaction between the fiber and the polymeric matrix for the composites with YM/APTS and YM/PP-g-MA, which corroborates the results of tensile and flexural strength, as well as with the spectra of FTIR in which the chemical modification of the fibers is observed. However, the results show that these treatments are promising in obtaining composites with recycled matrix with better properties.     

Mechanical and water absorption behaviors of corn stalk/sisal fiber‐reinforced hybrid composites

In this study, corn stalk flour (CSF) was used as filler instead of wood flour (WF) to prepare poly(vinyl chloride) (PVC) based wood plastic composite (WPC). In order to enhance the mechanical properties of the WPC, sisal fiber (SF) was introduced as reinforcer. The mechanical and the water absorption behaviors of WPC were investigated in detail. The results indicated that the chemical structure of CSF proved by FTIR was similar to that of WF. The effect of the hybridization of SF and CSF on the mechanical and water absorption behaviors of CSF/SF/PVC composite was studied. It was found that the introduction of SF of 5 mm in length resulted in improvement of the mechanical properties and had little effect on water absorption behavior. Scanning electron microscopy was carried out to observe the fracture surface of the composite. The distribution of CSF and SF in PVC was analyzed. Meanwhile, the hybrid enhancement mechanism of SF in PVC matrix was discussed. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46405.     

Wood flour/polylactide biocomposites toughened with polyhydroxyalkanoates

Polylactide (PLA)‐based wood–plastic composites (WPCs) were successfully manufactured by extrusion blending followed by injection molding. The effects of polyhydroxyanoates (PHAs) on the mechanical and thermal properties and the morphologies of the PLA‐based WPCs were investigated with mechanical testing, thermal analysis, and scanning electronic microscopy (SEM). The inclusion of PHAs in the PLA‐based WPCs produced an increase in the impact resistance and a decrease in the tensile strength. The brittle–ductile transition of the impact strength for the PLA‐based WPCs toughened with PHAs was confirmed when the wood flour content was between 15 and 35 wt %. SEM images showed that the fracture surfaces of the PLA‐based WPCs toughened with PHAs were rougher than that of their nontoughened counterparts. The ternary PLA‐based WPCs exhibited ductile fracture during mechanical testing. Differential scanning calorimetry (DSC) showed that addition of PHAs into the composites caused deviations of the cold crystallization temperature and melting temperature of PLA. Thermogravimetric analysis indicated that the PHAs reduced the thermal stability of the PLA‐based WPCs. PHAs can be a green toughening agent for PLA‐based WPCs. The specific properties evidenced by the biocomposites may hint at their potential application, for example, in the automotive industry and civil engineering. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Preparation of highly filled wood flour/recycled high density polyethylene composites by in situ reactive extrusion

Highly filled wood flour/recycled high density polyethylene (WF/RHDPE) composites were directly prepared by in situ reactive extrusion using a twin‐screw/single‐screw extruder system. The effects of dicumyl peroxide (DCP) content on extrusion pressure, rheological behavior, mechanical properties, fractured surface morphology of the composites, and melting temperature of RHDPE in the composites were investigated. The extrusion pressure and torque of WF/RHDPE composite melt increased with DCP content. Mechanical property tests and scanning electron microscopy analysis results confirmed that the interfacial interaction of the composites was improved by in situ reaction. The composites show lower melting peak temperature (T_m) than RHDPE. The cooling in profile extrusion shortened the crystallization time, resulting in decrease of crystalline order of RHDPE in the composites. There are no noticeable changes of T_m values with increasing DCP content. Comparative study on composites with maleic anhydride grafted polyethylene as compatibilizer demonstrated that mechanochemical treatment with DCP and maleic anhydride was an effective method to improve interfacial adhesion for WF/RHDPE composites. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Development of lightweight thermoplastic composites based on polycarbonate/acrylonitrile–butadiene–styrene copolymer alloys and recycled carbon fiber: Preparation,morphology, and properties

Thermoplastic composites of polycarbonate (PC)/acrylonitrile–butadiene–styrene copolymer (ABS) alloys reinforced with recycled carbon fiber (RCF) were prepared by melt extrusion through a twin‐screw extruder. The RCF was first cleaned and activated with a concentrated solution of nitric acid and was then surface‐coated with diglycidyl ether of bisphenol A as a macromolecular coupling agent. Such an approach is effective to improve the interfacial bonding between the fibers and the PC/ABS matrix. As was expected, the reinforcing potential of the RCF was enhanced substantially, and furthermore, the mechanical properties, heat distortion temperature, and thermal stability of PC/ABS alloys were significantly improved by incorporating this surface‐treated RCF. The composites also obtained a reduction in electrical resistivity. The morphologies of impact fracture surfaces demonstrated that the RCF achieved a homogeneous dispersion in the PC/ABS matrix due to good interfacial adhesion between the fibers and the matrix. In addition, the introduction of RCF into PC/ABS alloys also resulted in an increase in the storage moduli of the composites but a decrease in the loss factors. It is prospective that, with such good performance in mechanical data, heat resistance, and electrostatic discharge, the RCF‐reinforced PC/ABS composites exhibit a potential application in industrial and civil fields as high‐performance and lightweight materials. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Thermomechanical and cyclic behavior of biocomposites based on renewable thermoplastics from dimer fatty acids

Microbiocomposites based on renewable thermoplastic matrices such as thermoplastic polyurethane (TPU) and polyamide (DAPA), synthesized from dimer fatty acids, and high aspect ratio talc were prepared. TPU/DAPA blends and their corresponding biocomposites exhibited mechanical behavior, which is linked to those of the matrices and their relative contents, i.e., going from a typical semicrystalline behavior (DAPA) to an elastomeric one (TPU). The understanding of the thermomechanical and cyclic behavior of these advanced materials, particularly for TPU/DAPA with high TPU content, is detailed. Addition of particles of high aspect ratio natural talc (HAR) improved the storage modulus over the whole temperature range (almost five times with 5 wt % HAR). Under cyclic manipulation, the biocomposites displayed a stress softening related to the Mullins' effect. An increase of the hysteresis and the residual deformation with the HAR content has been shown. The hyperelastic models of Mooney–Rivlin and Ogden–Dorfmann, used to predict the loading and unloading behavior, fitted with experimental data. The present work also reports the experimental characterization of the deformation mechanisms of these renewable biocomposites through different microscopic techniques at different scales, such as atomic force, scanning electron and transmission electron microscopies. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44610.     

Mechanical performance and moisture absorption of various natural fiber reinforced thermoplastic composites

Natural fibers are seeing increased use in composite applications due to their reduced cost, low density, and environmental benefits (more sustainable and lower carbon footprint). Although many natural fiber systems have been examined over the last decade, there have been relatively few studies which have compared a variety of fiber types and processing methods directly in the same experimental set. In this study, natural fiber composites made from low density polyethylene (LDPE) and a variety of Canadian based fiber feedstocks were examined including hemp bast, flax bast, chemically pulped wood, wood chips, wheat straw, and mechanically pulped triticale. The effect of fiber type, fiber fraction and maleic anhydride polyethylene (MAPE) coupling agent on the mechanical properties and long‐term moisture absorption behavior was quantified. In general, addition of natural fiber to LDPE results in an increase in modulus (stiffness) with a corresponding loss of material elongation and impact toughness. Of the fiber types tested, composites made from chemically pulped wood had the best mechanical properties and the least moisture absorption. However, the use of MAPE coupling agent was found to significantly increase the mechanical performance and reduce moisture absorption for all other natural fiber types. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 969‐980, 2013     

Mechanical and thermal properties of polypropylene/recycled polyethylene terephthalate/chopped rice husk composites

The various ratios of recycled polyethylene terephthalate (rPET) into polypropylene (PP) filled with 40 parts chopped rice husk per hundred part of polymer have been studied. Composites were prepared using a corotating twin screw extruder at temperature zones of 165–215, well below 250°C (rPET mp temperature) and characterized by mechanical and thermal properties. To improve the compatibility between different components, PP grafted with maleic anhydride was added as a coupling agent in all the compositions studied. The results showed that the addition of rPET improved the tensile and flexural modulus and impact strength of the composite while reducing its tensile and flexural strength. The scanning electron microscopy micrographs of samples in the injection direction showed that some particle shaped rPET inside the composites appear as drawn fibrils and some appear as plates. Differential scanning calorimetric studies showed that the addition of rPET particles to the composites decrease the PP crystallization temperatures. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

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     

Self-healing polymer blend based on PETG and EMAA

In this work, novel immiscible polymer blends with remarkable self-healing properties were developed. The blends are based on poly(ethylene glycol-co-cyclohexane-1,4-dimethanol terephthalate) (PETG), a nonself-healing polymer, and the ionomer sodium-neutralized poly(ethylene-co-methacrylic acid) (EMAA), with self-healing abilities. The ratios of (PETG)/ (EMAA) was varied from 0 to 100% (w/w) and mixtures were prepared using a twin-screw melt extrusion. The blend studied compositions were characterized by scanning electron microscope, differential scanning calorimetry, dynamic mechanical analysis and self-repair tests. The results revealed that blends samples were able to self-repair damages created by Vickers microhardness indentations. The self-repair is presented through video records where the establishment of scars in the damaged area can be observed. For the composition 50/50 (w/w), the whole repair was observed due the synergic effect between polymer chain mobility, new chemical interactions promoted between PETG and EMAA, thus improving its self-healing ability.     

Polycarbonate biocomposites reinforced with a hybrid filler system of recycled carbon fiber and biocarbon: Preparation and thermomechanical characterization

In this article, we present the investigation of the use of a partly biobased hybrid reinforcement system to improve the mechanical properties of polycarbonate (PC). To minimize the amount of recycled carbon fibers (rCFs) used in this study, their initial quantity of 20% was reduced and replaced by pyrolyzed biocarbon (BC) particles in amounts of 5%, 10%, 15%, and 20%. The materials were prepared during an extrusion‐/injection‐molding processing procedure. In addition to basic mechanical tests (tensile, flexural, and Izod tests), the samples were also subjected to detailed dynamic mechanical analysis to determine the thermomechanical relationships, such as the C factor, entanglement density, adhesion factor, and reinforcing efficiency. The results confirm the positive effect of hybridization, especially for the samples with low BC contents. In relation to the 20% pure BC composites, the hybrid samples containing the same amount of mixed filler (10%; rCF10–BC10) achieved an almost triple (270%) increase in the tensile strength and a 35% increase in the modulus. The impact resistance was also increased by 170%. Differential scanning calorimetry analysis showed significant changes in the glass‐transition temperatures for the BC‐rich samples; this was due to the sensitivity of the PC matrix to the processing degradation. The application of a small quantity of epoxy‐based chain extender proved to be effective in reducing this unfavorable phenomenon. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46449.