Influence of temperature during overmolding on the tensile modulus of self-reinforced poly(ethylene terephthalate) insert

Self-reinforced polymer composites are thermoplastic materials for design of recyclable lightweight components. The combination of sheet forming and subsequent overmolding from these materials allows an efficient manufacturing process with function integration. This article investigates how temperature exposure during an overmolding cycle influences the tensile modulus, shrinkage, and warpage for an insert made from self-reinforced poly(ethylene terephthalate) (PET) when it is overmolded with polycarbonate (PC)/PET material. The temperature gradient that is induced by overmolding is simulated, and the results are validated through experiments. The results show that the insert reaches a temperature above the glass-transition temperature for the matrix material in the main part of the insert, which leads to relaxation of residual stresses and thereby a reduction of the tensile modulus up to 18% for the insert after overmolding. Even though overmolding is an efficient process, it requires thorough knowledge of how temperature influences the material when applied to self-reinforced composite materials. The study shows very interesting results, which can lead to new areas of applications for self-reinforced PET. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48334.     

Structure and properties of UHMWPE fiber/carbon fiber hybrid composites

Ultrahigh molecular weight polyethylene (UHMWPE) fiber/carbon fiber hybrid composites were prepared by inner‐laminar and interlaminar hybrid way. The mechanical properties, dynamic mechanical analysis (DMA), and morphologies of the composites were investigated and compared with each other. The results show that the hybrid way was the major factor to affect mechanical and thermal properties of hybrid composites. The resultant properties of inner‐laminar hybrid composite were better than that of interlaminar hybrid composite. The bending strength, compressive strength, and interlaminar shear strength of hybrid composites increased with an increase in carbon fiber content. The impact strength of inner‐laminar hybrid composite was the largest (423.3 kJ/m²) for the UHMWPE fiber content at 43 wt % to carbon fiber. The results show that the storage modulus (E′), dissipation factor (tan δ), and loss modulus (E″) of the inner‐laminar hybrid composite shift toward high temperature remarkably. The results also indicate that the high‐performance composite with high strength and heat resistance may be prepared by fibers' hybrid. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 1880–1884, 2006     

High shear melt‐processing of fiberglass‐reinforced poly(trimethylene) terephthalate composites

As the demand for polymer‐matrix composites (PMC) expands in order to replace traditional materials, processing of the PMC is increasingly vital, as the morphology and properties are processing dependent. Typically, thermoplastic PMCs are processed in at least two heat‐intensive steps, including a pre‐compounding step in order to achieve good mixing followed by a part fabrication step. The key aim of this study is to prepare a fiberglass‐reinforced poly (trimethylene terephthalate) (FG‐PTT) composite using a one‐step, high shear melt‐processing method that achieves both compounding and part fabrication. The morphology, thermal properties, and mechanical properties are characterized to determine the effect of FG reinforcement on this renewable biopolymer. This novel method produces a FG‐PTT composite with superior mixing and tensile strength, as well as enhanced toughness, in one processing step, reducing polymer degradation and fiber attrition, as well as, time, energy, and cost requirements. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42714.     

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.     

Weld line improvement of short fiber reinforced thermoplastics with a movable flow obstacle

Short fiber reinforced (SFR) thermoplastics are ideal materials from which to manufacture complex technical parts in high volumes with low energy expenditure. The orientation of the fibers, and hence their reinforcing effect, depends strongly on the nature of the cavity and on the injection molding process. One disadvantage of SFR thermoplastics is a significant decrease in mechanical properties in the areas of the weld lines, due to subopt imal fiber orientation as the melt streams reunite at these points. Common mold‐based and process‐based optimization techniques alter the fiber orientation after the formation of the weld line. The mold‐based approach presented here, on the other hand, operates at the time the weld line is formed: by redirecting the melt streams, it moves the weld line and improves the fiber orientation. A prototype mold is described, and samples produced from it with both standard and modified weld lines are compared with flawless specimens. The new technique yields a large rise in flexural strength and a smaller but significant improvement in tensile properties. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42025.     

Experimental analysis of temperature and crystallinity profiles of wood sawdust/polypropylene composites during cooling

The temperature profiles of wood sawdust/polypropylene (PP) composite melts during cooling were experimentally investigated with a cooling jacket apparatus connected to the end of an injection‐molding machine. Real‐time melting temperature was measured with an unsheathed thermocouple array coupled with a high‐speed data‐acquisition unit. The crystallinity level of the solidified composites was evaluated with an X‐ray diffractometer. Before the crystallization temperature (T_c) was reached, the cooling rate of the melt layer near the wall was greater than that near the center. After T_c was reached, the opposite behavior was observed. Wood sawdust content did not affect the general temperature and crystallinity profiles across the duct diameter but led to more nonuniform temperature profiles across the duct diameter. The sawdust particles could act as a nucleating agent during the nucleation stage to increase T_c of the PP and as an interfering agent during the crystal growth stage to decrease the overall crystallinity level of the PP. The temperature and crystallinity profiles were not affected by the coolant flow rate. The normalized induction time changed with reduced radius (r/R, where r is the distance between the central duct to any point along the cross‐section of the duct and R is the duct radius) positions and coolant flow rate, especially for neat PP and PP composites with a low sawdust content (10 wt %). © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 1896–1905, 2006     

Surface treatment of eucalyptus wood for improved HDPE composites properties

In this study, the effect of Eucalyptus globulus wood (UE) used as a filler (5–20% w/w) on the physical and thermal properties of high-density polyethylene (HDPE) composites was evaluated. To improve the compatibility with HDPE, the wood was modified (TE) using crude glycerol derived from biodiesel production. The addition of 20% (w/w) of UE or TE led to more rigid and durable composite materials compared to neat HDPE (about 50 or 100% increase in tensile strength, respectively). Composites also revealed 55–75°C higher temperatures at maximal degradation rates. The advantageous behavior of TE over UE in composites was attributed to the improvement of surface morphology of modified wood and it is better compatibility with the HDPE as revealed by surface energy analysis. The changes in wetting behavior of HDPE and ensuing HDPE-TE composites (contact angles of ca 72 and 80°, respectively) explain the matrix-filler interactions. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48619.     

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.     

Physical and mechanical characterization of jute fabric composites

As‐received and washed jute fabrics were used as reinforcement for a thermoset resin. The mild treatments performed on the jute fabrics did not significantly affect their physical and thermal behaviors. The washed fibers absorbed less water than the unmodified (as received) ones, indicating that the coating used to form the fabrics was hygroscopic. Measurements of the fiber mechanical properties showed a high dispersion due to fiber irregularities, although the values obtained were in agreement with data reported in the literature. These results were also analyzed with the Weibull method. To investigate the effect of the jute treatments on the interface properties, impact, compression, and tensile tests were carried out. The composites made from as‐received jute had the highest impact energy, which was probably associated with weak interfacial adhesion. Composite samples behaved more ductilely in compression than in tensile situations due to the brittle characteristics of the resin used as matrix. The effect of the orientation of the fibers with respect to the direction of the applied force in the different mechanical tests was also studied. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 639–650, 2005     

Preferred orientation of chopped fibers in polymer-based composites processed by selective laser sintering and fused deposition modeling: Effects on mechanical properties

The orientation of reinforcing fibers in polymer-based composites greatly affects their mechanical features. It is known that different orientations of continuous fibers in the stacked layers of a laminate play a crucial role in providing an isotropic mechanical behavior, while the alignment of chopped fibers in injection molding of composites results in a degree of anisotropy. Recent additive manufacturing techniques have offered a way of controlling the fiber orientation. This article aims to investigate the effect of fiber orientation on the mechanical properties of polyamide/carbon fiber composites processed by fused deposition modeling and selective laser sintering. Tensile samples which had different fibers and layer interface with respect to the sample axis (and therefore to the tensile load) were produced. Tensile tests were performed at different strain rates; the tensile properties and the fracture surface morphology were correlated with the processing method and the sample microstructure. The best strength and stiffness were observed when the fibers and the layer interfaces were parallel to the sample axis.     

The mechanical and tribological properties of nitric acid‐treated carbon fiber‐reinforced polyoxymethylene composites

The carbon fibers have been exposed to nitric acid oxidation treatments and introduced into polyoxymethylene composites (POM/CF). The nitric acid treatment increases the number of the flaws, roughness of the surface, and disorder of carbon atoms on fiber, as well as introduces reactive functional groups, which could lead to a better mechanical bonding between fiber and the matrix. It is shown that the impact strength and fiber‐matrix adhesion in composites (POM/mCF) are superior to those for POM/CF composites. Simultaneously, the addition of mCF improves flexural strength and modulus relative to virgin POM significantly. Average friction coefficient values of POM/CF composites are lower than that of POM/mCF composites. As the percentage of fiber increases, the trend of wear ratio of the composites goes down initially and bumps up afterwards. The results indicate that the proper contents of CF and mCF in composites range from 5 wt % to 20 wt %. Scanning electron microscopy of worn surface morphology has revealed that the main wear mechanism of the composites were adhesive wear and ploughing wear. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41812.     

Preparation of soft wood–plastic composites

To extend the applications of wood–plastic composites (WPCs), soft WPCs were prepared with ethylene vinyl acetate (EVA) and wood flour (WF) as major components via a two‐step process involving two‐roll mixing and compression molding. The effect of the various factors, such as WF, unsaturated fatty acid (UFA), and dicumyl peroxide contents, on the mechanical properties, processability, and morphology of the WPCs was investigated in detail. The addition of UFA could effectively improve the processability and flexibility of the composites. The in situ grafting reaction between UFA and EVA considerably improved the adhesion of the WF and resin matrix. Consequently, soft WPCs with good performances in flexibility and processability were successfully obtained. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Fabrication and characterization of SiC-ZTA ceramic composites by hot pressing

Al₂O₃/ZrO₂/SiC ceramic composites with different SiC contens have been prepared by hot pressuring. The effect of SiC content on the microstructure and mechanical properties of composites have been studied. The results show that SiC has obvious grain refinement effect on ZTA ceramics and change the fracture mode of the matrix from intergranular fracture to transgranular fracture. Simultaneously, it has been found that the mechanical properties of the material are significantly enhanced in comparison with ZTA matrix. The highest strength is acquired at 10% SiC content, the flexural strength and toughness are obtained when the SiC content is 15 vol%, and the values are 18.86 GPa, 1262 MPa and 6.13 MPa m^1/2, respectively. The mechanisms of hardening, strengthening and toughening have been discussed.     

Mechanical and thermal characterization of compression moulded polylactic acid natural fiber composites reinforced with hemp and lyocell fibers

This research evaluates the effects of PLA/PP blend ratio and Lyocell/hemp mixture ratio on the morphology, water absorption, mechanical and thermal properties of PLA‐based composites. The composites were fabricated with 30 mass % hemp using compression moulding. As a reference composites made from PP were also studied. Combining of hemp and Lyocell in PLA composite leads to the reduction of moisture absorption and can improve the impact, tensile, flexural properties when compared with PLA/hemp. Composite based on the PLA/PP blend‐matrix could not improve the tensile and flexural properties compared with PLA/hemp, however; the lighter composite with better impact properties was obtained. The crystallization temperature of the PLA‐PP/hemp increased compared with pure PLA. This result was also confirmed by the SEM micrographs. The moisture absorption of PLA‐PP/hemp was higher than PLA/hemp. Based on theoretical analysis of DMTA data, there was favorable adhesion in all composites. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40534.     

Mechanical,water absorption,and morphology of recycled polymer blend rice husk flour biocomposites

Rice husk flour (RHF) biocomposites based on uncompatibilized and compatibilized recycled high density polyethylene/recycled polyethylene terephthalate (rHDPE/rPET) with ethylene‐glycidyl methacrylate (E‐GMA) copolymer were prepared through a two‐step extrusion and hot pressing with fiber loadings of 40, 60, and 80 wt %. Results showed that tensile and flexural properties increased. However, the elongation to break and impact strength decreased as the RHF loading increased. Compatibilizing polymer blend matrices can further enhance the mechanical properties. Water absorption (WA) test were examined in distilled and seawater. It is interesting to note that for composites made from uncompatibilized matrix, the calculated D and K_SR were lower in seawater, but for the compatibilized matrix composites, the D and K_SR obtained were generally lower in distilled water. However, compatibilization of rHDPE/rPET has been markedly reduced the WA and thickness swelling. Scanning electron microscope analysis of the compatibilized matrix composites confirmed the improved interfacial bonding of matrix–matrix and filler–matrix phases. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41494.     

Effect of twisting on mechanical properties of GF/PP commingled hybrid yarns and UD‐composites

This study was conducted due to the necessity for improving the processability of commingled yarns during textile processing, in particular dense 3D preform weaving. Open structure of the commingled yarns caused higher production stops. As a possible solution, GF/PP commingled yarns with different twisting levels were produced. Effect of twisting on the mechanical properties of commingled yarns and on their compression molded UD composites are determined. Further tests were executed about yarn/yarn and yarn/metal friction of twisted commingled yarns, which are important properties during textile processing. Theoretical approaches such as a yarn model with linear bar elements and lamina equation with an equivalent angle distortion of over‐delivery proved useful to relate the structural parameters and mechanical properties. As a result, twisting did not significantly affect the modulus of elasticity of UD‐composites, however, the tensile strength of UD‐composites were reduced by further processing even without twisting. Therefore, small twisting levels can be applied on commingled yarns to improve processability of dense preforms without significantly affecting the mechanical performance. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Experimental investigation and statistical analysis of additively manufactured onyx-carbon fiber reinforced composites

Availability of additive manufacturing has influenced the scientific community to improve on production and versatility of the components created with several associated technologies. Adding multiple substances through superimposing levels is considered as a part of three-dimensional (3D) printing innovations to produce required products. These technologies are experiencing an increase in development nowadays. It requires frequently adding substance and has capacity to fabricate extremely complex geometrical shapes. However, the fundamental issues with this advancement include alteration of capacity to create special products with usefulness and properties at an economically viable price. In this study, significant procedural parameters: layer designs/ patterns (hexagonal, rectangular and triangular) and infill densities (30%, 40%, and 50%) were considered to investigate into their effects on mechanical behaviors off fused deposition modeling or 3D-printed onyx-carbon fiber reinforced composite specimens, using a high-end 3D printing machine. Mechanical (tensile and impact) properties of the printed specimens were conclusively analyzed. From the results obtained, it was observed that better qualities were achieved with an increased infill density, and rectangular-shaped design exhibited an optimum or maximum tensile strength and energy absorption rate, when compared with other counterparts. The measurable relapse conditions were viably evolved to anticipate the real mechanical qualities with an accuracy of 96.4%. In comparison with other patterns, this was more closely predicted in the rectangular design, using regression models. The modeled linear regression helps to define the association of two dependent variables linked with properties of the dissimilar composite material natures. The models can further predict response of the quantities before and also guide practical applications.     

Reactive hot pressing of SiC-ZrC composites at low temperature

SiC-ZrC composites with relative density in excess of 99% were prepared by reactive hot pressing (RHP) of SiC and ZrH₂ at 1800 °C for 1 h. The reaction between SiC and ZrH₂ resulted in the formation of ZrC_1-x. The formation process and densification behavior during RHP process were investigated. Low temperature densification of SiC-ZrC composites is attributed to the formed nonstoichiometric ZrC_1-x and the removal of SiO₂ impurity on the surface of SiC particles. As reinforced phase, ZrC_1-x has inhibiting effect on the abnormal grain growth of SiC, resulting in homogeneous microstructure of fine SiC grains. Adding 10 wt% ZrH₂ to SiC, the formed SiC-4.62 vol% ZrC composite exhibited better mechanical properties (Vickers hardness of 27.6 ± 0.7 GPa, flexure strength of 448 ± 38 MPa, fracture toughness of 6.0± 0.3 MPa·m^1/2, respectively) than monolithic SiC ceramic.     

In situ composites from blends of polycarbonate and a thermotropic liquid‐crystalline polymer: The influence of the processing temperature on the rheology,morphology, and mechanical properties of injection‐molded microcomposites

This work was aimed at understanding how the injection‐molding temperature affected the final mechanical properties of in situ composite materials based on polycarbonate (PC) reinforced with a liquid‐crystalline polymer (LCP). To that end, the LCP was a copolyester, called Vectra A950 (VA), made of 73 mol % 4‐hydroxybenzoic acid and 27 mol % 6‐hydroxy‐2 naphthoic acid. The injection‐molded PC/VA composites were produced with loadings of 5, 10, and 20 wt % VA at three different processing barrel temperatures (280, 290, and 300°C). When the composite was processed at barrel temperatures of 280 and 290°C, VA provided reinforcement to PC. The resulting injection‐molded structure had a distinct skin–core morphology with unoriented VA in the core. At these barrel temperatures, the viscosity of VA was lower than that of PC. However, when they were processed at 300°C, the VA domains were dispersed mainly in spherical droplets in the PC/VA composites and thus were unable to reinforce the material. The rheological measurements showed that now the viscosity of VA was higher than that of PC at 300°C. This structure development during the injection molding of these composites was manifested in the mechanical properties. The tensile modulus and tensile strength of the PC/VA composites were dependent on the processing temperature and on the VA concentrations. The modulus was maximum in the PC/VA blend with 20 wt % VA processed at 290°C. The Izod impact strength of the composites tended to markedly decrease with increasing VA content. The magnitude of the loss modulus decreased with increasing VA content at a given processing temperature. This was attributed to the anisotropic reinforcement of VA. Similarly, as the VA content increased, the modulus and thus the reinforcing effect were improved comparatively with the processing temperature increasing from 280 to 290°C; this, however, dropped in the case of composites processed at 300°C, at which the modulus anisotropy was reduced. Dynamic oscillatory shear measurements revealed that the viscoelastic properties, that is, the shear storage modulus and shear loss modulus, improved with decreasing processing temperatures and increasing VA contents in the composites. Also, the viscoelastic melt behavior (shear storage modulus and shear loss modulus) indicated that the addition of VA changed the distribution of the longer relaxation times of PC in the PC/VA composites. Thus, the injection‐molding processing temperature played a vital role in optimizing the morphology‐dependent mechanical properties of the polymer/LCP composites. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Dynamic tensile and shear storage moduli of PEG/silica-polymorph composites

The effect of silica polymorphs on the thermomechanical properties of 0, 5, 10, and 20 wt % silica particles-reinforced-based poly(ethylene glycol) (PEG) composites have been studied as a function of temperature using dynamic mechanical analysis (DMA). The silica polymorphs exhibited quartz (Q), cristobalite (C), and amorphous (A) phases, which were obtained by processing natural silica sand. The DMA thermomechanical properties were determined in tensile (E) and shear (G) modes. The maximum storage moduli (E′ and G′) were achieved by samples with 20 wt % silica for all type of fillers. These values increased approximately 12 times for PEG/Q, 10 times for PEG/A, and 11 times for PEG/C composites compared to the pure PEG. Furthermore, the Poisson's ratio values of the composites were filler phase dependent, that is, 0.39–0.47 for PEG/Q, 0.15–0.18 for PEG/A, and somewhat anomalous for PEG/C composites. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47372.