Measurement and numerical prediction of fiber‐reinforced thermoplastics' thermal conductivity in injection molded parts

Recent improvements in injection molding numerical simulation software have led to the possibility of computing fiber orientation in fiber reinforced materials during and at the end of the injection molding process. However, mechanical, thermal, and electrical properties of fiber reinforced materials are still largely measured experimentally. While theoretical models that consider fiber orientation for the prediction of those properties exist, estimating them numerically has not yet been practical. In the present study, two different models are used to estimate the thermal conductivity of fiber reinforced thermoplastics (FRT) using fiber orientation obtained by injection molding numerical simulation software. Experimental data were obtained by measuring fiber orientation in injection molded samples' micrographs by image processing methods. The results were then compared with the numerically obtained prediction and good agreement between numerical and experimental fiber orientation was found. Thermal conductivity for the same samples was computed by applying two different FRT thermal conductivity models using numerically obtained fiber orientation. In the case of thermal conductivity, predicted results were consistent with experimental data measurements, showing the validity of the models. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39811.     

Wood‐fiber/high‐density‐polyethylene composites: Compounding process

The compounding process directly influenced the compounding quality of wood–polymer blends and finally affected the interfacial bonding strength and flexural modulus of the resultant composites. With 50 wt % wood fiber, the optimum compounding parameters for the wood‐fiber/high‐density‐polyethylene blends at 60 rpm were a temperature of 180°C and a mixing time of 10 min for the one‐step process with a rotor mixer. The optimum compounding conditions at 90 rpm were a temperature of 165°C and a mixing time of 10 min. Therefore, a short compounding time, appropriate mixing temperatures, and a moderate rotation speed improved the compounding quality of the modified blends and the dynamic mechanical properties of the resultant composites. The melt torque and blend temperature followed a polynomial relationship with the loading ratio of the wood fiber. The highest melt torque and blend temperature were obtained with 50% wood fiber. The coupling treatment was effective for improving the compatibility and adhesion at the interface. The two‐step process was better than the one‐step process because the coupling agents were more evenly distributed at the interface with the two‐step process. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 2570–2578, 2004     

Thermal degradation and combustion behavior of intumescent flame‐retardant polypropylene with novel phosphorus‐based flame retardants

The objective of this study was to develop an environmentally friendly fire‐retardant polypropylene (PP) with significantly improved fire‐retardancy performance with a novel flame‐retardant (FR) system. The system was composed of ammonium polyphosphate (APP), melamine (MEL), and novel phosphorus‐based FRs. Because of the synergistic FR effects among the three FRs, the FR PP composites achieved a V‐0 classification, and the limiting oxygen index reached as high as 36.5%. In the cone calorimeter test, both the peak heat‐release rate (pHRR) and total heat release (THR) of the FR PP composites were remarkably reduced by the incorporation of the novel FR system. The FR mechanism of the MEL–APP–FR–PP composites was investigated through thermogravimetric analysis and char residue characterization, and the results reveal that the addition of MEL–APP–FRs promoted the formation of stable intumescent char layers. This led to the reduction of pHRR and THR and resulted in the improvement of the fire retardancy. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45962.     

Polysilazane‐based heat‐ and oxidation‐resistant coatings on carbon fibers

Carbon fibers must be protected from a high‐temperature oxidizing environment because, at approximately 500°C and above, the fibers exhibit reduced mass and strength stability. The fibers can be protected by the application of thermal coatings, which simultaneously improve the adhesive properties of the carbon fibers in the composite materials. Polysilazanes are a new family of heat‐resistant polymer coatings that are converted into silicone carbide or silicone nitride ceramic structures at high temperatures. The converted ceramics are resistant to the effects of high temperatures. In this research work, polysilazane‐based coatings were applied to carbon filament (CF) rovings with the dip‐coating method. Tensile testing at room temperature and under thermal stress was carried out to assess the mechanical and thermomechanical properties of both coated and uncoated rovings. Scanning electron microscopy and energy‐dispersive X‐ray analysis were performed to evaluate the surface topographical properties of the coated and uncoated rovings. Thermogravimetric analysis was executed to determine the thermal stability of the polymer coatings. The coating performance on the CF rovings was determined by assessment of the test results obtained. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Performance and structure changes of the aromatic co‐polysulfonamide fibers during thermal‐oxidative aging process

The changes in performance during thermal‐oxidative aging process of the aromatic co‐polysulfonamide (co‐PSA) fibers over a broad temperature range from 250 °C to 320 °C have been investigated. In addition, the mechanism of thermal‐oxidative aging process has been studied by using structural information obtained from the fibers at varying length scales. The results showed that a significant reduction in tensile strength was observed compared with that of initial modulus during aging process. Macroscopically, thermal‐oxidative aging mainly causes color changes of fibers and thermally induced macro defects begin to appear only at 320 °C for 100 h. On a micro level, the crystal structure of fibers remained stable and did not show significant changes expect that aging at 320 °C. In addition, thermo‐degradation as well as crosslinking has been observed primarily in amorphous region. With the increase of temperature and time duration, the crosslinking became more dominant and crosslinking density increases. Correspondingly, the fibril length decreases due to degradation and then increases due to the formation of crosslinked structures within the fibers. The results suggest that molecular degradation is the main cause of strength loss and the formation of crosslinking structure within the fibers contributes to the retention of modulus and improvement of creep resistance. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44078.     

Rheological and thermal properties of thermoplastic natural rubbers based on poly(methyl methacrylate)/epoxidized‐natural‐rubber blends

Epoxidized natural rubbers (ENRs) with epoxide levels of 10, 20, 30, 40, and 50 mol % were prepared. The ENRs were later blended with poly(methyl methacrylate) (PMMA) with various blend formulations. The mixing torque of the blends was observed. The torque increased as the PMMA contents and epoxide molar percentage increased in the ENR molecules. Furthermore, the shear stress and shear viscosity of the polymer blends in the molten state increased as the ENR content and epoxide molar percentage increased in the ENR molecules. Chemical interactions between polar groups in the ENR and PMMA molecules might be the reason for the increases in the torque, shear stress, and viscosity. All the ENR/PMMA blends exhibited shear‐thinning behavior. This was observed as a decrease in the shear viscosity with an increase in the shear rate. The power‐law index of the blends decreased as the ENR contents and epoxide molar percentage increased in the ENR molecules. However, the consistency index (or zero shear viscosity) increased as the ENR contents and epoxide molar percentage increased. A two‐phase morphology was observed with scanning electron microscopy. The small domains of the minor components were dispersed in the major phase. For the determination of blend compatibility, two distinct glass‐transition‐temperature (T_g) peaks from the tan δ/temperature curves were found. Shifts in T_g to a higher temperature for the elastomeric phase and to a lower temperature for the PMMA phase were observed. Therefore, the ENR/PMMA blends could be described as partly miscible blends. According to the thermogravimetry results, the decomposition temperatures of the blends increased as the levels of ENR and the epoxide molar percentage increased. The chemical interactions between the different phases of the blends could be the reason for the increase. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 3561–3572, 2004     

Thermally stable low‐density polyethylene/polyhydroxybutyrate pairs: Synergy between organomodified nanoclay and LDPE‐g‐MAH

Nanocomposites of low‐density polyethylene/polyhydroxybutyrate (LDPE/PHB) containing organomodified montmorillonite (OMMT) and/or LDPE grafted maleic anhydride (LDPE‐g‐MAH) were prepared with a wide range of composition ratios using a vertical co‐rotating twin‐screw microCompounder. To infer the effect of OMMT and LDPE‐g‐MAH on the thermal stability of prepared nanocomposites, all samples were characterized by thermogravimetric analysis while changing clay and compatibilizer contents. Accordingly, two commonly used kinetic models (Coats–Redfern and Horowitz–Metzger) were employed to correlate the thermal stability of the samples with kinetic parameters, including activation energy and pre‐exponential factor. Furthermore, morphological features of LDPE/PHB in the presence or absence of OMMT and LDPE‐g‐MAH were studied using scanning electron microscopy, transmission electron microscopy, and wide‐angle X‐ray diffraction analysis. It was found that for a specific OMMT composition ratio (1 wt %), the thermal stability is enhanced due to an exfoliated structure. However, for samples containing more organoclay (>=3 wt %), the thermal stability was reduced showing the competition between the barrier effect of organoclay platelets and the catalyzing effect of ammonium salts. Moreover, when using LDPE‐g‐MAH as compatibilizer, it acted as a good coupling agent in all compositions in LDPE major phase systems in contrast to PHB major phase samples. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45922.     

Thermal induced shape‐memory and self‐healing of segmented polyurethane containing diselenide bonds

Herein, we synthesized a series of polyurethane copolymers (PUs) with poly(1,4‐butylene adipate) glycol as soft segment and 2,4‐toluene diisocyanate as well as extenders including 1,4‐butanediol and di(1‐hydroxyethylene) diselenide as hard segment. The chemical structure, thermal property, crystallization behavior, shape memory, and self‐healing performances of the PUs were systematically characterized by a series of experiments. It was found that the PU2 containing a higher diselenide component (～33 mol %) exhibited both shape memory and self‐healing behaviors under a moderate temperature (～57 °C). Meanwhile, the PUs showed a good repeatability of shape memory function, and their fixity and recovery ratios were all above 90%. Additionally, the dynamic exchangeable feature of diselenide bonding endues the PUs chains with an acceptable reprocessability and self‐healing performances, and the PU2 sample could be healed for five times by thermal treatment with the healing efficiencies above 70%. This work provides a heuristic perspective for the development of shape memory and self‐healing materials. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46326.     

Comparison of the guarded‐heat‐flow and transient‐plane‐source methods for carbon‐filled nylon 6,6 composites: Experiments and modeling

In this study, two different carbons (synthetic graphite particles and carbon fiber) were added to nylon 6,6, and the resulting composites were tested for thermal conductivity. The first goal of this work was to compare through‐plane thermal conductivity results from the guarded‐heat‐flow method and the transient‐plane‐source method. The results showed that both test methods gave similar through‐plane thermal conductivity results for composites containing 10–40 wt % synthetic graphite and for composites containing 5–40 wt % carbon fiber. The advantages of using the transient‐plane‐source method were that the in‐plane thermal conductivity was also measured and the experimental time was shorter than that of the guarded‐heat‐flow method. The second goal of this work was to develop and use a detailed finite‐element analysis to model heat transfer within a carbon‐filled nylon 6,6 composite sample for the transient‐plane‐source method and compare these results to actual experimental results. The results showed that the finite‐element model compared well with the actual experimental data. The finite‐element model could be used in the future as a design tool to predict the dynamic thermal response of different composite materials for many applications. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci, 2006     

Dopamine‐functionalized poly(vinyl alcohol) elastomer with melt processability and self‐healing properties

A dopamine‐functionalized poly(vinyl alcohol) (PVA) elastomer with melt processability and self‐healing properties was prepared by a new chemical route of graft modification, that is, PVA carboxylation and a carbodiimide reaction. The conventional modifier for PVA sacrificed the intrinsic hydrogen‐bonding interactions and dramatically decreased the mechanical strength. The modifier dopamine, as a catechol derivative, has two hydroxyl groups, which formed hydrogen bonds with the hydroxyl groups of PVA; it also has one benzene ring, which increased the thermal stability. We found that the introduction of dopamine into the PVA molecular structure lowered the melting point, improved the thermal stability, broke the crystalline structure, and enabled thermal processing. Moreover, the modified PVA possessed good mechanical properties, could be self‐healed, and is believed to have potential applications in many fields. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45072.     

Biobased blends of poly(propylene carbonate) and poly(hydroxybutyrate‐co‐hydroxyvalerate): Fabrication and characterization

Poly(propylene carbonate) (PPC), a CO₂‐based bioplastic and poly(hydroxybutyrate‐co‐hydroxyvalerate) (PHBV) were melt blended followed by injection molding. Fourier transform infrared spectroscopy detected an interaction between the macromolecules from the reduction in the OH peak and a shift in the C?O peak. The onset degradation temperature of the polymer blends was improved by 5% and 19% in comparison to PHBV and PPC, respectively. Blending PPC with PHBV reduced the melting and crystallization temperatures and crystallinity of the latter as observed through differential scanning calorimetry. The amorphous nature of PPC affected the thermal properties of PHBV by hindering the spherulitic growth and diluting the crystalline region. Scanning electron micrographs presented a uniform dispersion and morphology of the blends, which lead to balanced mechanical properties. Incorporating PHBV, a stiff semi‐crystalline polymer improved the dimensional stability of PPC by restricting the motion of its polymer chains. © 2016 The Authors Journal of Applied Polymer Science Published by Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134 , 44420.     

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.     

Rate‐dependent self‐healing behavior of an ethylene‐co‐methacrylic acid ionomer under high‐energy impact conditions

In this work, the mechanical and the self‐healing behaviors of an ethylene‐co‐methacrylic acid ionomer were investigated in different testing conditions. The self‐healing capability was explored by ballistic impact tests at low‐velocity, midvelocity, and hypervelocity bullet speed; different experimental conditions such as sample thickness and bullet diameter were examined; in all impact tests, spherical projectiles were used. These experiments, in particular those at low and midspeed, allowed to define a critical ratio between sample thickness and bullet diameter below which full repair was not observed. After ballistic damage, the healing efficiency was evaluated by applying a pressure gradient through tested samples. Subsequently, morphology analysis of the affected areas was made observing all tested samples by scanning electron microscope. This analysis revealed different characteristic features of the damaged zones affected at different projectile speed. Stress–strain curves in uniaxial tension performed at different temperatures and strain rates revealed yield strength and postyield behavior significantly affected by these two parameters. A rise of temperature during high strain rate tests in the viscoplastic deformation region was also detected. This behavior has a strong influence on the self‐repairing mechanism exhibited by the studied material during high‐energy impact tests. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 1949–1958, 2013     

Controlling micro‐ and nanofibrillar morphology of polymer blends in low‐speed melt spinning process. Part I. Profiles of PLA/PVA‐filament parameters along the spinline

The profiles of PLA/PVA filament parameters (e.g., temperature, velocity, tensile stress, and apparent elongational viscosity) along the spinline in the low‐speed melt spinning process under various spinning conditions were investigated. Owing to the combination of the filament velocity and filament temperature measurements using laser doppler velocimetry (LDV) and infrared thermography, respectively, the fiber formation zone was determined. The length of the fiber formation zone obtained from filament velocity profiles is always shorter than that obtained from the filament temperature profiles ( . Obviously, this unexpected phenomenon occurs for low spinning speeds due to the axial heat conduction effect of the filament along the spinline and the nonuniform radial temperature distribution through the cross‐sectional thick filament. Another remarkable finding is related to the Nusselt number which has been found as nearly constant along the spinline in the low‐speed melt spinning process. Thus, mathematical simulations of the filament temperature profiles will be simplified drastically. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44258.     

Rheological,thermal, and mechanical properties of P (3HB‐co‐4HB) and P (3HB‐co‐4HB)/EVA blends

Poly(3‐hydroxybutyrate‐co‐4‐hydroxybutyrate) [P(3HB‐co‐4HB)] fiber and P(3HB‐co‐4HB)/EVA fiber were obtained by single screw extrusion machine. The rheology of P(3HB‐co‐4HB) and P(3HB‐co‐4HB)/EVA blends was characterized by capillary rheometer, and the chemical groups of the blends were characterized with Fourier transform infrared spectroscopy (FT‐IR). The crystallization behavior and thermal, mechanical and elastic properties of the fibers were measured by differential scanning calorimeter (DSC), thermogravimetric analyzer (TGA) and single fiber strength tester, respectively. Besides, the moisture regain and drying shrinkage rates of the fibers were tested. These results showed that P(3HB‐co‐4HB)/EVA blends have better flowability, crystallinity, and thermal stability than P(3HB‐co‐4HB) fiber. The fracture strength of the P(3HB‐co‐4HB)/EVA fiber decreases with increasing the EVA content, but the elongation at break shows the contrary tendency. The rebound resilience ratio of P(3HB‐co‐4HB)/EVA fiber reaches 100%. Both moisture regain and drying shrinkage increase first and then decrease with increasing the EVA content. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 41206.     

Phosphate ester groups‐containing ricinoleic acid‐based Ca/Zn: Preparation and application as novel thermal stabilizer for PVC

Phosphate ester groups containing ricinoleic acid‐based Ca/Zn (LPPRA‐Ca and LPPRA‐Zn) stabilizer was successfully synthesized from ricinoleic acid (RA) and used as thermal stabilizers for poly(vinyl chloride) (PVC). These thermal stabilizers were characterized by Fourier transform infrared spectrometry, ¹H nuclear magnetic resonance, and inductively‐coupled plasma atomic emission spectroscopy. The effects of LPPRA‐Ca/LPPRA‐Zn, CaSt₂/ZnSt₂, and other stabilizers on the thermal stability of PVC were studied through Congo Red test, discoloration tests, thermogravimetric analysis (TGA), TGA–infrared, and TGA–mass spectrometry. The thermal stability tests show that LPPRA‐Ca/LPPRA‐Zn displays the best initial color stability and long‐term thermal stability for PVC. The superior performance is attributed to the synergistic effect of LPPRA‐Ca and LPPRA‐Zn. Moreover, a lower Zinc content of LPPRA‐Zn in PVC helps to decrease the “zipper dehydrochlorination” of the product, which contributes to a better initial thermal stability. Except for the better stabilization performance, LPPRA‐Ca/LPPRA‐Zn also displays better plasticization performance for PVC compared with other stabilizers. A possible stabilizing mechanism of PVC/LPPRA‐Ca/LPPRA‐Zn system was presented. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45940.     

Influence of process parameters on mechanical properties of physically foamed,fiber reinforced polypropylene parts

Due to the high complexity of the foaming technology, the relationship between processing and final properties of parts produced is not completely understood. Investigating the causality chain Processing–Morphology–Properties is of great importance, especially for the automotive industry, in order to be able to tailor the mechanical properties of foamed parts. This article examines and qualifies the effects of seven process parameters (melt/mold temperature, degree of foaming, injection speed, delay time, gas content, and back pressure) on biaxial bending and flexural behavior—the predominant deformation mechanisms in interior automotive applications—of foamed plaques, using the MuCell process. The results clearly show that three major factors (mold temperature, degree of foaming, and delay time) have significant impact on the mechanical properties of the foamed parts. For a clear understanding of these interactions, computed tomography scans of certain plaques are correlated to process parameters and mechanical performance. This article should forge a bridge between production and performance. © 2018 The Authors. Journal of Applied Polymer Science published by Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47275.     

Preparation of heat‐resistant gradient‐index polymer optical fiber rods based on poly(N‐isopropylmaleimide‐co‐methyl methacrylate)

Using the interfacial gel polymerization method, a heat‐resistant gradient‐index polymer optical fiber (GI POF) was developed based on the copolymer of methyl methacrylate (MMA) and N‐isopropylmaleimide (IPMI) as the matrix material and bromobenzene (BB) as dopant. The gradient distribution of IPMI in the GI POF rod was determined by element analysis. IPMI had great advantage in improving glass transition temperature (T_g) and forming a gradient‐index profile. There was a significant enhancement in the heat‐resistant property in comparison with a conventional GI POF rod. The combination of high thermal stability and easy fabrication makes the novel BB–IPMI–MMA system very suitable for heat‐resistant GI POF. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 280–283, 2003     

Imide‐containing ladder polyphenylsilsesquioxanes with high thermal stability and thermoplastic properties

This work reports for the first time the synthesis of ladder polyphenylsilsesquioxanes containing imide building blocks as parts of the main parallel chains. The ladder structure of the synthesized polymers was documented by means of small angle X‐ray scattering (SAXS) measurements. The obtained ladder polymers exhibit stability with respect to decomposition up to temperatures as high as 460°C; additionally, they have melting points far below their decomposition temperatures, which make them interesting candidate materials for thermoplastic processing. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40085.     

Effect of process variables on bulk development of air‐textured poly(trimethylene terephthalate) bulk continuous filaments

Bulk development of air‐textured poly(trimethylene terephthalate) (PTT) bulk continuous filaments was studied by varying two texturing parameters, yarn preheating and texturing hot air temperatures. The yarns were subsequently heat treated from 80 to 160°C. Bulk was found to go through a maximum with increasing heat‐treatment temperature because of two competing mechanisms. Upon heat treatment, the fiber shrunk and developed bulk; heat treatment also simultaneously induced structural reorganization through annealing and stabilized the fiber against shrinkage. When the later mechanism became dominant, bulk development decreased with further increase of heat‐treatment temperature. The temperature at which the maximum occurred increased when the yarn preheating or texturing air temperatures were increased. Depending on the extent of annealing and structural reorganization during yarn preheating and during texturing, fibers with equivalent bulk measured at a single temperature did not behave the same way over a range of heat‐treatment temperatures. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 1011–1017, 2004