Study on the preparation and mechanical properties of injection‐moulded wood‐based plastics

The objectives of this study were to prepare injection‐moulded wood‐based plastics and to characterize their mechanical properties. Injection‐moulded wood‐based plastics with satisfactory flexural (65.7 MPa) and tensile strengths (30.1 MPa) were successfully obtained through a simple reaction of mulberry branch meal with phthalic anhydride (PA) in 1‐methylimidazole under mild condition. The X‐ ray diffraction results indicated complete disruption of the crystallinity of cellulose because the pattern obtained for esterified fiber was almost a straight line without any peaks. The peaks in the Fourier transform infrared spectroscopy spectra (1738 and 748 cm^?1) and NMR spectra (173.3 and 133.5 ppm) indicated the attachment of 0‐carboxybenzoyl groups onto the wood fibers via ester bonds. The differential scanning calorimetry curves showed that the glass transition temperature decreased with increasing weight percentage gain (WPG). The derivative thermogravimetric analysis curves indicated that esterified wood fiber was less thermally stable than the untreated fiber and that the component tends to be homogeneous with increasing WPG. Scanning electron microscope revealed that the fractured surfaces of most samples were smooth and uniform but that high temperature and less PA dosage could lead to the appearance of holes and cracks. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41376.     

Effect of an obstacle during processing on the weld line of injection‐molded glassy polystyrene: Microhardness study

The microhardness (H) technique is used to characterize the quality of the weld line in injection‐molded glassy polystyrene by means of a cylindrical obstacle. In particular, the effect of the indentation location (closer or further from the obstacle edge parallel to the injection direction and across the weld line), both on the surface and in the bulk, was examined. Only for surface measurements close to the obstacle (up to 10 mm) a well‐pronounced decrease in H (～30%), followed by a sharp increase in a narrow distance (0.20–0.25 mm), was observed. For the bulk measurements on the same location a slight decrease in H was detected. Additional H measurements made up to 60 mm from the obstacle for both cases showed that the weld line remains undetectable. The results obtained reveal that the presence of a cylindrical obstacle causes the formation of a weld line on and near the surface only at distances not exceeding the obstacle diameter. At larger distances, because of the effective mutual interdiffusion of polymer chains, the two parallel fronts coming from the two sides of the obstacle developed a homogeneous material without any weld line according to the microhardness test. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 3362–3367, 2004     

Self‐oscillatory neck propagation in polymers

The oscillatory neck propagation during cold drawing of PET was studied. The mechanism of self‐oscillations is heat instability of neck propagation. Oscillations are observed at high velocities when the draw stress increases with an increase in cross‐head speed. Neck propagation is described by three equations, which were solved numerically. The solution of these equations predicts appearance of oscillations at high elongation velocities in agreement with experimental observations. The necessary condition of appearance of oscillations in any polymer is existence of some interval of cross‐head speeds V, where the draw stress decreases with an increase in V. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Proton‐induced crosslinking of CR 6‐2 polycarbonate

CR 6‐2 polycarbonate samples were irradiated using different fluences (10¹¹–10¹⁴ ions/cm²) of 1 MeV protons. The structural modifications in the proton‐irradiated CR 6‐2 samples have been studied as a function of fluence using different characterization techniques such as X‐ray diffraction, intrinsic viscosity of the liquid samples, as a measure of the mean molecular mass, Fourier transform infrared spectroscopy, thermogravimetric analysis, differential thermal analysis, refractive index, color difference, and mechanical properties. The results indicate that the irradiation of CR 6‐2 detector at the fluence range 1 × 10¹²–5 × 10¹⁴ ions/cm² causes intermolecular crosslinking and allows the formation of covalent bonds between different chains, leading to a more compact structure of CR 6‐2 polymer, which resulted in an improvement in its thermal, optical, and mechanical properties. Also, this crosslinking reduces the ordering structure and increases the amorphous regions that enhance the polymer resilience. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Thermal and morphological behavior of irradiated composite materials based on injection‐moulded recycled polyethylene terephthalate

The effect of gamma irradiation and short glass fiber (SGF) on the thermal and morphological behavior of the recycled poly (ethylene terephthalate) (rPET) in the presence of reactive additive (epoxy resin, 2 wt %) has been investigated. Characterization of the resulted composites to evaluate the effect of incorporation the SGF and irradiation by means of differential scanning calorimetry, X‐ray diffraction, thermal gravimetric analysis, and scanning electron microscopy (SEM). The results show that the SGF and epoxy resin behave as nucleating agents for the crystallization of rPET. A noticeable increase in the rPET thermal stability in the presence of both SGF and epoxy resin has been observed. Furthermore, the rPET melting temperature (T_m) slightly decrease in the presence of the SGF and remains nearly constant with the incorporation of the epoxy resin. On the other hand, the rPET crystallinity percent (X%) decreases in the presence of SGF and gamma irradiation. The SEM showed that a layer of epoxy resin was coated onto the SGF in the rPET matrix. This coating layer raises the interfacial shear strength between the fiber and polymer matrix and also increases with gamma irradiation. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2008     

Hygrothermal aging and tensile behavior of injection‐molded rice husk‐filled polypropylene composites

The effect of the filler volume fraction on the tensile behavior of injection‐molded rice husk‐filled polypropylene (RH–PP) composites was studied. Hygrothermal aging behavior was also investigated by immersing the specimens in distilled water at 30 and 90°C. The kinetics of moisture absorption was studied from the amount of water uptake by specimens at regular interval times. It was found that the diffusion coefficient and the maximum moisture content are dependent on the filler volume fraction and the immersion temperatures. Incorporation of RH into the PP matrix has led to a significant improvement in the tensile modulus and a moderate improvement in the tensile strength. Elongation at break and energy at break, on the other hand, decreased drastically with the incorporation of the RH filler. The extent of deterioration incurred by hygrothermal aging was dependent on the immersion temperature. Both the tensile strength and tensile modulus deteriorated as a result of the combined effect of thermal aging and moisture attack. Furthermore, the tensile properties were not recovered upon redrying of the specimens. Scanning electron microscopy was used to investigate the mode of failure of the RH–PP composites. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 742–753, 2001     

Low‐temperature aging of baddeleyite‐based Ca‐TZP ceramics

The aging kinetics during low‐temperature aging of calcia‐stabilized tetragonal zirconia polycrystal (Ca‐TZP) ceramics prepared by high‐energy milling of natural zirconia mineral (baddeleyite) was studied by X‐ray diffraction under hydrothermal treatment conditions. Aging kinetics was investigated for ceramics with different contents of calcia. It was found that the kinetics may be well‐described within Johnson‐Mehl‐Avrami‐Kolmogorov model. Model parameters were determined by data fitting procedure. Change in exponential factor within Johnson‐Mehl‐Avrami‐Kolmogorov model with time is shown. Analytical model to describe aging kinetics is proposed. The transformation nucleation rate, initial diameter, and depth of the transformed areas and their growth rates are estimated. Degradation of hardness and fracture toughness is also reported for Ca‐TZP after low‐temperature aging for different contents of the stabilizer.     

Nanofiber‐reinforced polymers prepared by fused deposition modeling

Vapor‐grown carbon fibers (VGCFs), a practical model nanofiber for single‐walled carbon nanotubes, were combined with an acrylonitrile–butadiene–styrene (ABS) copolymer to create a composite material for use with fused deposition modeling (FDM). Continuous filament feedstock materials were extruded from Banbury mixed composites with a maximum composition of 10 wt % nanofibers. Issues of dispersion, porosity, and fiber alignment were studied. SEM images indicated that the VGCFs were well dispersed and evenly distributed in the matrix and that no porosity existed in the composite material following FDM processing. VGCFs aligned both in the filament feedstock and in the FDM traces suggested that nanofibers, in general, can be aligned through extrusion/shear processing. The feedstock materials were processed into test specimens for mechanical property comparisons with unfilled ABS. The VGCF‐filled ABS swelled less than did the plain ABS at similar processing conditions due to the increased stiffness. The tensile strength and modulus of the VGCF‐filled ABS increased an average of 39 and 60%, respectively, over the unfilled ABS. Storage modulus measurements from dynamic mechanical analysis indicated that the stiffness increased 68%. The fracture behavior of the composite material indicated that the VGCFs act as restrictions to the chain mobility of the polymer. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 3081–3090, 2003     

Micromechanical properties of injection‐molded starch–wood particle composites

The micromechanical properties of injection‐molded starch–wood particle composites were investigated as a function of particle content and humidity conditions. The composite materials were characterized by scanning electron microscopy and X‐ray diffraction methods. The microhardness of the composites was shown to increase notably with the concentration of the wood particles. In addition, creep behavior under the indenter and temperature dependence were evaluated in terms of the independent contribution of the starch matrix and the wood microparticles to the hardness value. The influence of drying time on the density and weight uptake of the injection‐molded composites was highlighted. The results revealed the role of the mechanism of water evaporation, showing that the dependence of water uptake and temperature was greater for the starch–wood composites than for the pure starch sample. Experiments performed during the drying process at 70°C indicated that the wood in the starch composites did not prevent water loss from the samples. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 4893–4899, 2006     

Mechanical properties of injection‐molded isotactic polypropylene/roselle fiber composites

Natural fiber‐thermoplastic composite materials, based on their cost‐effectiveness and environmental friendliness, have attracted much interest both scientifically and technologically in recent years. Other advantages of natural fibers are good specific strength, less abrasion, and less irritation upon inhalation (in comparison with some common inorganic fillers). In the present contribution, roselle (Hibiscus sabdariffa L.) fibers were chosen and used as reinforcing fillers for isotactic polypropylene (iPP) for the first time, due mainly to the cost‐effectiveness and natural abundance on Thai soil. Processibility and mechanical properties of the resulting composites were investigated against the type and the mean size of the fibers. The results showed that the highest mechanical properties were observed when roselle bast fibers were incorporated. When whole‐stalk (WS) fibers (i.e., the weight ratio of bast and core fibers was 40 : 60 w/w) were used, moderate mechanical properties of the resulting composites were realized. The optimal contents of the WS fibers and the maleic anhydride‐grafted iPP compatibilizer that resulted in an improvement in some of the mechanical properties of the resulting composites were 40 and 7 wt %, respectively. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 3291–3300, 2006     

Short‐term flexural creep behavior and model analysis of a glass‐fiber‐reinforced thermoplastic composite leaf spring

Present work investigated the short‐term flexural creep performance of fiber reinforced thermoplastic injection molded leaf springs. Unreinforced polypropylene, 20 wt % short and 20 wt % long glass fiber reinforced polypropylene materials were injection‐molded into constant thickness varying width mono leaf spring. Short‐term flexural creep tests were performed on molded leaf springs at various stress levels with the aid of in‐house developed fixture integrated with the servo‐hydraulic fatigue machine. Spring rate reduction is reported as an index for the accumulated damage. Experimental creep performance of molded leaf springs for 2 h was utilized to predict the creep performance with the aid of four parameter HRZ model and compared with 24‐h experimental creep data. Test results revealed that HRZ model is sufficient enough to predict short‐time flexural creep performance of engineering products over wide range of stress. Test results also confirmed the suitability of long fiber reinforced thermoplastic material for creep application over other considered materials. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Protein/glycerol blends and injection‐molded bioplastic matrices: Soybean versus egg albumen

Two well‐known proteins have been selected in order to produce bioplastics through injection molding: a soy protein isolate (SPI) and an egg white albumen concentrate (EW). Each of them has been thoroughly mixed with glycerol (40 wt %) and the blend then obtained have been characterized by means of rheological and thermomechanical techniques, which allowed the optimization of the processing moulding conditions (cylinder temperature, 60°C–65°C; mould temperature, 120°C; post‐injection pressure, 500–600 bars). Once bioplastics were obtained, their thermomechanical and tensile properties, as well as their water uptake capacity and transparency were evaluated. Bioplastics containing EW showed higher values in the elastic and loss moduli, E′ and E″, from ?30°C to 130°C, than the corresponding SPI bioplastic. However, they both showed qualitatively the same evolution with temperature, where E′ and E″ decreased up to a plateau at high temperatures. When examining their tensile and water uptake properties is found that SPI bioplastics are more ductile and present enhanced water uptake behavior over EW bioplastics, which on the other hand possess higher Young's modulus. SPI seems to provide tougher bioplastics, being an excellent option for potential superabsorbent applications, whereas EW would suit for those applications requiring higher mechanical properties. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 42980.     

The Influence of Molecular Orientation on the Yield and Post‐Yield Response of Injection‐Molded Polycarbonate

The influence of the flow history experienced during injection molding on the mechanical properties of amorphous polymers is investigated. It is demonstrated that flow‐induced molecular orientation only causes a small anisotropic effect on the yield stress, which can be regarded as insignificant with respect to its absolute value. Its influence on the post‐yield strain‐hardening response is also shown to be imperceptible, in contrast to a orientation which is applied during deformation below the glas transition.

     

Weld‐line sensitivity of injected amorphous polymers

The effects of the processing parameters on the weld‐line mechanical properties of polystyrene (PS) and polycarbonate (PC) were investigated. PS was very sensitive to the presence of a weld line, showing property reductions of up to 70%. However, this sensitivity was mainly connected to the surface notch at the weld line. When this notch was removed, behavior close to that of unwelded specimens was obtained. The injection temperature was the main processing parameter because it affected the macromolecular diffusion speed and, therefore, influenced the weld quality. A direct relationship between the distance of molecular diffusion and the fracture mechanism was established. PC had a low weld‐line sensitivity, despite being an amorphous polymer like PS. The difference between these materials was connected to the different sizes of the surface defects and to the different entanglement densities, which influenced the relaxation time and the global behavior (brittle–ductile). © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 644–650, 2004     

Mechanical properties and stem cell adhesion of injection‐molded poly(ether ether ketone) and hydroxyapatite nanocomposites

A nanocomposite of poly(ether ether ketone) (PEEK) with 10 wt % hydroxyapatite (HA) was produced by extrusion and injection molding. Afterward, the samples were thermally treated. Thermal and short‐ and long‐term mechanical characterizations of the samples were made. The adhesion of human adipose stem cells (h‐ASCs) on the samples was also monitored. The ultimate tensile strength (UTS) and elastic modulus values of the nanocomposite were found to be much higher than those of trabecular bone. The impact strength of PEEK was not modified by HA; this suggested that there was no formation of large agglomerates of nanoparticles that could concentrate the stresses. With regard to fatigue life, both the thermally and nonthermally treated nanocomposites did not fail after 10⁶ cycles when maximum stresses of 30 and 50% of the UTS were applied, but they failed when the maximum applied stress was 75% of the UTS and behaved as cortical bone. After 5 days of culturing, the h‐ASCs had a higher proliferation in the nanocomposite than in pure PEEK because of the presence of HA. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41748.     

A DMA study of the interfacial changes on injection‐molded iPP/mica composites modified by a p‐phenylen‐bis‐maleamic acid grafted atactic polypropylene

Present work concerns to the study of the dynamic mechanical and thermal responses of selected polypropylene (iPP)/mica composites with a modified interface from the matrix side by using a p‐phenylen‐bis‐maleamic acid grafted atactic polypropylene, coming from a byproduct of industrial polymerization reactors. Thus, the study is mainly focused on the 75/25 iPP/mica ratio since it was identified in previous works as providing the maximum inter mica particle distance to assure they should participate in the overall process of dissipation of the mechanical energy supplied to the composites. Hence, the present dynamic mechanical analysis discussion tries to correlate the damping responses of the injection‐molded composites with those previously obtained but over compression molded composites as the basis of further studies all along the compositional iPP/mica map. Therefore, the latter let us, on the one hand, to follow how the main values of the different dynamic mechanical analysis parameters vary because of the interfacial modifier presence, and on the other, to develop a robust correlation between them and the corresponding macroscopic mechanical parameters. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45366.     

Remendable polymers via reversible Diels–Alder cycloaddition of anthracene‐containing copolymers with fullerenes

Poly(lauryl methacrylate)s with anthracene moieties in the side chain were converted with C₆₀‐fullerene and phenyl‐C₆₁‐butyric acid methyl ester (PCBM), resulting in new remendable (self‐healing) polymeric materials. The utilization of differently substituted anthracene monomers enabled the tuning of the reactivity and the resulting mechanical properties. Copolymers with different contents of the anthracene moieties were synthesized and characterized using size exclusion chromatography, ¹H nuclear magnetic resonance (NMR) spectroscopy as well as differential scanning calorimetry (DSC). ¹H NMR spectroscopic studies were utilized in order to investigate the reversibility of the Diels–Alder reaction between copolymers with C₆₀‐fullerene and PCBM, respectively, in solution. In order to investigate the conversion of the polymers with C₆₀‐fullerene and PCBM in bulk, additionally, DSC, nanoindentation, rheology, atomic force microscopy (AFM), 3D microscopy, simultaneous thermal analysis (STA) and FT‐Raman investigations were performed. The fullerene‐containing copolymers could be healed in a temperature range of 40–80 °C. Consequently, a new generation of low temperature remendable polymers could be established. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45916.     

Residual orientation in injection‐moulded plaques of atactic‐polystyrene II: The effect of molecular weight

Injection moulding of polymers is a well‐established technique for the production of increasingly complex articles, and residual molecular orientation is a matter of considerable interest. A single matrix of commercial atactic polystyrene was systematically blended with deuterated polystyrene chains of five different weight fractions and the orientation investigated using small angle neutron scattering (SANS), optical birefringence and thermal shrinkage. The strengths and limitations of the experimental techniques used to measure residual orientation are explored and highlighted the unique contribution of SANS to observe ensemble averaged molecular orientation using deuterated polymers. The residual molecular orientation was found to vary with the molecular weight of the deuterated chains with an increase with increasing molecular weight. The observed correlations lead to a better understanding of the processing parameters that influence the degree of residual orientation on the molecular scale. Such information is valuable in the selection of the polymer matrix, mould design, and processing conditions. POLYM. ENG. SCI., 58:1332–1341, 2018. © 2017 Society of Plastics Engineers     

Residual orientation in injection‐moulded plaques of atactic‐polystyrene I: The effect of processing conditions

Injection moulded polymer articles often have residual macromolecular or crystalline orientation which can have a significant impact on the optical and mechanical properties of the moulded article. Small angle neutron scattering (SANS) was used to measure the molecular shape and orientation of deuterated blends of injection moulded polystyrene. For ～1‐mm‐thick mouldings of uniform rectangular cross‐section, the eccentricity in the SANS pattern gave a direct measure of the residual molecular orientation over the length scale ～100–1,500 Å. The residual orientation was found to vary significantly with injection moulding conditions with comparative residual orientation decreasing with decreasing mould fill‐time, and increasing with mould thickness and moulding temperatures. The orientation was found to be a minimum in the centre of the mould and highest near the surface and the average orientation at a particular position in the mould was found to be strongly correlated with the volume of material deposited as a solid skin layer during injection moulding. POLYM. ENG. SCI., 58:1322–1331, 2018. © 2017 Society of Plastics Engineers     

Time-dependent birefringence in glassy polymers during stress-relaxation and recovery

The birefringence of polystyrene and polycarbonate have been measured during uniaxial stress relaxation tests. The birefringence of polystyrene shows an instantaneous positive increment on applying a tensile deformation; during stress relaxation the value showed a time-dependent change in the negative direction and the total birefringence eventually became more negative than the value measured prior to the deformation. On unloading, the overall trend was for the birefringence to change towards the level measured in the as-prepared sample prior to deformation but an initial departure in the opposite direction was observed. With polycarbonate, the birefringence changed instaneously on applying the deformation and remained steady during stress relaxation. On unloading the birefringence fell instaneously by an amount less than the increment observed on applying the deformation. Thereafter the birefringence continued to fall, approaching the original value with a time constant similar to that governing stress relaxation. These results are interpreted with reference to the molecular structures, in particular the location of the highly polarizable aromatic rings.