Injection Molding Shrinkage and Mechanical Properties of Polypropylene Blends

Polypropylene (PP) blends based on isotactic polypropylene (iPP), propylene-ethylene block copolymer (bPP), and propylene–ethylene random copolymer (rPP) were prepared by melt blending and the effects of content of bPP and rPP on the shrinkage during solidification and storage and mechanical properties of the blends were studied. It was found that the addition of polypropylene copolymer could effectively reduce the processing shrinkage of iPP and the lowest shrinkage of the blends was achieved at a loading of 2 wt% bPP or rPP. The flexural modulus and tensile strength of the blends decreased a little while the impact strength and elongation at break were improved greatly compared with those of iPP.     

Thermorheological Properties and Thermal Stability of Polyethylene/Wood Composites

The thermal stability, flame retardancy, thermorheological, and mechanical properties of polyethylene/wood flour (PE/WF) composites were characterized. By time–temperature superposition treatment, addition of WF was found to lead to a complexity in the thermorheological behaviors in low-density PE/wood composites. However, high-density PE/wood counterparts showed no obvious thermorheological complexity. The effects of WF and ammonium polyphosphate contents on the thermorheological behavior and thermal stability were also studied. The current work should be of practical significance for the optimization of wood/plastic composite) formulae, as well as for further investigations on correlations between processing and performance of polymer composites.     

Mechanical Properties and Crystallization Behavior of Polycarbonate/Polypropylene Blends

The mechanical properties, morphology, and crystallization behavior of polycarbonate (PC)/polypropylene (PP) blends, with and without compatibilizer, were studied by tensile and impact tests, scanning electron microscopy (SEM), X-ray diffraction (XRD), and differential scanning calorimetry (DSC). The tensile and impact strengths of PC/PP blends decreased with increasing the PP content due to poor compatibility between the two phases. But the addition of compatibilizer improved the mechanical properties of the PC/PP blends, and the maximum value of the mechanical properties, such as tensile and impact strengths of PC/PP (80/20 wt%) blends, were obtained when the compatibilizer was used at the amount of 4 phr. The SEM indicated that the compatibility and interfacial adhesion between PC and PP phases were enhanced. DSC results that showed the crystallization and melting peak temperatures of PP increased with the increase of the PP content, which indicated that the amorphous PC affected the crystallization behavior. However, both the PC and compatibilizer had little effect on the crystallinity of PP in PC/PP blends based on both the DSC and XRD patterns.     

Epitaxial Crystallization of Linear Polyethylene in Blends with Isotactic Polypropylene

The structure and morphology of extrusion-oriented ribbons of polypropylene/polyethylene blends is described. The blends with 20%, 30%, and 40% of oriented isotactic polypropylene fibrils show homo- and heteroepitaxial structures. Partial mutual solubility of the blend components influenced the melting and crystallization behavior.     

Preparation of Ultrahigh Molecular Weight Polyethylene/WS2 Composites for Bulletproof Materials and Study on Their Bulletproof Mechanism

Ultrahigh molecular weight polyethylene (UHMWPE)/WS₂ nanoparticle fibers were prepared by adding inorganic fullerene-like (IF) WS₂ nanoparticles treated by a coupling agent to the precursor solution of UHMWPE. The influence of WS₂ nanoparticles on the microstructure and properties of UHMWPE fibers were characterized by the scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), and mechanical property measurements. The bulletproof performance of the UHMWPE/WS₂ composite was tested by a bullet-shock test, and the bulletproof mechanism of the UHMWPE/WS₂ composite was preliminarily studied. The results showed that WS₂ nanoparticles could be uniformly dispersed in the UHMWPE fiber. After incorporating of WS₂ nanoparticles, the UHMWPE fibers became stiffer and tougher than the pristine ones. In particular, the modulus of the fibers increased from 1203 to 1326 cN/dtex. The introduction of IF-WS₂ nanoparticles led to significantly improved bulletproof performance of UHMWPE fibers.     

Mechanical Properties and Rheological Behavior of Dynamically Vulcanized Trans-Polyisoprene/Polypropylene Blends

The degree of dynamic vulcanization, mechanical properties, rheological behavior, and the ageing-resistant performance of thermoplastic vulcanizates (TPVs) based on Trans 1,4-polyisoprene/polypropylene (TPI/PP) blends with the blend ratios of 70/30, 60/40, and 50/50 were investigated. The results showed that TPI fully dynamically vulcanized in the Haake mixer chamber when mixed with PP, and the specimen with the blend ratio 70/30, for the same sulfur content in all samples, had the lowest cross-linking degree of the TPI phase. The shear viscosity of TPI/PP-TPVs dropped as the shear rate increased and the specimen with the blend ratio 70/30 had a relatively greater shear viscosity in the region of shear rates less than 1000 s^?1. With the antiageing agent Vulkanox 4020 NA (Bayer) added, all the TPI/PP-TPVs showed good ageing characteristics, and the specimen with the blend ratio 70/30 possessed the best mechanical properties.     

Physical and Thermal Properties of High-Density Polyethylene Film Modified with Polypropylene and Linear Low-Density Polyethylene

Abstract

In view of the toughness and processing difficulty of high-density polyethylene (HDPE) film, the HDPE was modified by polypropylene (PP) and linear low density polyethylene (LLDPE), and the melt index, haze, dart impact strength, elongation at break were characterized. In addition the infrared spectra (IR), scanning electron microscopy (SEM), infrared image analysis, and differential scanning calorimetry (DSC) data were obtained. The results showed that the toughening effect of the 10%PP/30%LLDPE/60%HDPE composition was the best; the haze was reduced 6% and its dart impact strength and elongation at break were increased by 27.3% and 47%, respectively, relative to the pure HDPE. The blend of 10%PP/30%LLDPE/60%HDPE had compatibility. The melting point of the 10%PP/30%LLDPE/60%HDPE blend film increased by 5?°C compared with the pure HDPE film, with the results indicating the application fields of HDPE film could be widened.     

Influence of the Polymer/Inorganic Filler Interface on the Mechanical,Thermal, and Flame Retardant Properties of Polypropylene/Magnesium Hydroxide Composites

The relationship between the interface structure and the macroscopic properties of composites composed of isotactic polypropylene (iPP) and magnesium hydroxide (MH) was investigated with a focus on mechanical properties, thermal stability, and flame retardancy. Surface treatment of MH was carried out using dodecanoic acid (DA) and dodecylphosphate (DP), both of which interacted with MH to form submonolayer coverages. Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) revealed that both organic reagents adhere to the MH surface via ionic interactions. Even low amounts of organic reagents on the MH surface were sufficient to improve the mechanical, thermal, and flame retardant properties of the composites. The incorporation of 1.8 wt% of DP in (70/30) iPP/MH-DP composite decreased the peak heat release rate (PkHRR) to 39% compared with that of neat iPP. Since the effects of DA with the same dodecyl chains were not significant, it is concluded that the phosphate groups in DP provide flame retardancy.     

Assessment of Compatibility in Polypropylene/Poly(lactic acid)/Ethylene Vinyl Alcohol Ternary Blends: Relating Experiments and Molecular Dynamics Simulation Results

Two systems of polypropylene (PP), poly(lactic acid) (PLA) and ethylene vinyl alcohol copolymer (EVOH) ternary blends having different compositions were extruded in a co-rotating twin screw extruder. The first system was PP/PLA (75/25) with various EVOH contents, the second one was PP/EVOH (75/25) having various PLA contents. The effects of composition on the morphology and the tensile and impact properties of the blends were investigated. There were increases in the tensile modulus and tensile strength with an increase in the EVOH and PLA contents in the first and second systems, respectively. A molecular dynamics (MD) simulation was used to investigate the compatibility between the components. Prediction of the miscibility of the blends was carried out by determining the interaction parameters (χ), mixing energies (ΔH_mix), phase diagrams and Gibbs free energies. The MD simulation showed a UCST behavior for the components. Moreover, the simulation results showed a compatibilizer effect for the EVOH component. The experimental values of the dynamic mechanical thermal analysis (DMTA) and mechanical properties were correlated to the MD results. There was a good correlation between the MD and DMTA results. The modulus values using the parallel and Davis models were near to the experimental ones. A good fitting to the mixture law with addition of EVOH confirmed a good compatibilzing effect of it between the PP and PLA components.     

Co-crystallization of Blends of High-density Polyethylene with Linear Low-density Polyethylene: An Investigation with Successive Self-nucleation and Annealing (SSA) Technique

Two kinds of polyethylenes, high-density polyethylene (HDPE) with few chain branches and short-chain branched linear low-density polyethylene (LLDPE) with a relatively larger average molecular weight, were melt blended together in various mass ratios based on consideration of their practical applications. After identifying the good compatibility of the blends, their crystallization behaviors were studied by the successive self-nucleation and annealing (SSA) technique. The SSA analysis showed that not merely the number of melting fractions in the SSA curves changed with the blend composition, but also the content of the first two melting fractions at high temperature of SSA curves showed a positive deviation and a negative deviation with the blend composition, respectively. These phenomena, as well as the interesting appearance of a stepped increase of the lamellar thickness of each fraction with the highest temperature in each sample, indicated that co-crystallization occurred between HDPE and LLDPE. The results from wide-angle X-ray diffraction (WAXD) supported the conjecture obtained by the SSA analysis.     

Steady Shear Rheological Behavior,Mechanical Properties,and Morphology of the Polypropylene/Carbon Nanotube Nanocomposites

Nanocomposites based on polypropylene (PP) and multiwall carbon nanotubes (MWNT) have been prepared through melt blending. Scanning electron microscopy (SEM) observations indicate that nanotubes were dispersed almost homogeneously throughout the matrix; however, some aggregates were also observed at high nanotubes loading. Rheological studies showed that at low shear rates, there is an increase in steady shear viscosity and shear stress of samples with increasing of nanotubes concentration. However, at high shear rates nanocomposites behave like pure PP. The activation energy of flow showed an increasing trend and has a maximum at 1wt% MWNT content. It was found that incorporation of nanotubes causes a remarkable decrease in surface and volume resistivity values of the polymeric matrix. The presence of CNTs improved the tensile and flexural properties of the polymeric matrix.     

Self-Lubricating Ultrahigh Molecular Weight Polyethylene Thin Films with Excellent Wear Resistance at Light Friction Loads on Glass and Silicon

Thin films of ultrahigh molecular weight polyethylene (UHMWPE) were prepared on glass and silicon using a dip-coating technique, followed by removal of the decahydronaphthalene solvent at 140?°C for 20?hours and cooling in the oven in air. The wetting ability of the films was investigated by a contact angle method. The tribological behavior of the films was investigated using a ball-on-disk configuration in reciprocating mode. The reciprocating frequency of 4?Hz and single sliding distance of 5?mm used corresponded to a sliding speed of 40?mm/s. The counterface was a GCr15 steel ball with diameter of 3?mm and the normal frictional loads were 10–300?g. The worn surfaces on the films and wear scars on the steel ball were observed and analyzed by scanning electron microscopy (SEM). It was found that the surface morphologies of the films on glass and silicon were different, which is ascribed to the difference in thermal conductivity of the glass and silicon. Evaporation of the solution caused micro-orifices in the films on glass. The water contacting angle of about 87° on the films on the two substrates was similar to that of bulk UHMWPE. Their friction coefficient of about 0.1–0.2 indicated the films were self-lubricating. The wear life of the films decreased quickly with the increase of friction load. At light friction loads, the films showed excellent wear resistance. Extrusion was believed to be the main wear mechanism of the films.     

Mechanical and Thermal Properties of Polypropylene/Silica Aerogel Composites

Polypropylene (PP) composites including various amounts of silica aerogel (SA) microparticles were prepared by melt mixing in an internal mixer. The morphology and microstructure of the prepared composites were investigated by scanning electron microscopy (SEM). Mechanical properties of the samples, including elastic modulus, tensile stress, elongation and stress at break, were measured by tensile tests. In addition, the other mechanical features, including Izod impact strength, hardness and wear resistance, were evaluated and then related to the structure of the PP/SA composites. Furthermore, the thermal characteristics of the composites, such as heat deflection temperature and thermal stability, were studied by thermal gravimetric analysis (TGA). The SEM photographs indicated the satisfactory SA particles dispersion for the compositions of 1% and 3% but agglomeration of the aerogels at higher SA contents. Since the composites became stiffer, the impact and tensile strength decreased. The addition of the SA to the PP matrix yielded harder samples with lower weight loss and coefficients of friction in wear tests. The TGA evaluations confirmed that the presence of SA promoted and upgraded the thermal stability and heat deflection temperature of PP. The thermal results proved the superior potential of PP as an insulator when the SA particles were added.     

Crystallization Behavior and Mechanical Properties of Microinjection Molded High Density Polyethylene Parts

Ultra-thin high density polyethylene (HDPE) parts with two different molecular weights were prepared by microinjection molding (MIM). The dependence of crystalline morphology and orientation, as well as the resulting mechanical properties of the samples, on molecular weight is described. The toughness of the high-molecular-weight (HMW) sample was over 2 times that of the low-molecular-weight (LMW) one, in parallel with a significant increase of tensile strength. Microstructure characterizations, including differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD) and small-angle X-ray scattering (SAXS), were performed to investigate the variations of the microstructure. It is suggested that the increased crystallinity and higher degree of both molecular and lamellar orientation were beneficial to the enhancement of strength of the HMW sample. SAXS results showed that a highly oriented crystalline structure, i.e. shish-kebabs, were formed in parts of both of the two HDPE. Furthermore, a larger number of shish and kebab structure or lamellae was formed in the HMW sample due to the fact that the crystallinity was increased and the lamellar thickness and lateral crystallite size was reduced. Therefore, a stronger physical cross-linking network was formed in the HMW sample because of the increased connection points, which was in favor of the notable improvement of toughness. We suggest this issue is of great significance for achieving materials with high performance by tailoring the microstructure.     

Microstructure and Mechanical Properties of Isotactic Polypropylene Films Fabricated via Melt-Extrusion and Uniaxial-Stretching

In this work, isotactic polypropylene (iPP) melt was slowly extruded through a slit die of a single-screw extruder. Once the iPP melt left the die, it was uniaxially stretched at different stretching rates (SRs). Via this process its microstructure can be manipulated, it was subsequently investigated by wide-angle X-ray diffraction (WAXD), small-angle X-ray scattering (SAXS), differential scanning calorimetry (DSC), polarized optical microscopy (POM), and Fourier transform infrared spectroscopy (FTIR). Furthermore, the mechanical properties (including tensile strength, modulus, toughness, and strain-hardening) were investigated. The results showed that the tensile strength and modulus of the melt-stretched iPP films gradually increased with increasing SRs. In addition, the toughness and elongation at break showed maximum values for iPP films melt-stretched at 30 cm/min. Moreover, compared with other melt-stretched films, the iPP films melt-stretched at 90 cm/min exhibited an obvious strain-hardening behavior at lower strain.     

Phase Structure,Thermal, and Mechanical Properties of Polypropylene/Hollow Glass Microsphere Composites Modified with Maleated Poly(ethylene-octene)

Maleated poly(ethylene-octene) (POE-g-MAH), as a compatilizer and toughener, was incorporated in polypropylene/hollow glass microspheres (PP/HGM) binary composites, and the phase structure and thermal and mechanical properties of these composites were investigated. Scanning electron microscopy analysis indicated that the phase structure of ternary composites could be controlled by POE-g-MAH and the surface treatment of HGM. Fourier transform infrared spectroscopy revealed that there was an amidation reaction between the treated HGM and POE-g-MAH during melt compounding. Differential scanning calorimetry suggested that the crystallization and melting behaviors of ternary composites were influenced by phase structure. Evaluation of mechanical properties showed that the amide linkage between the treated HGM and POE-g-MAH was favorable for improving the properties of ternary composites.     

Surface Modification of Ultrahigh-molecular-weight Polyethylene Fibers with Coupling Agent during Extraction Process

Ultrahigh molecular weight polyethylene (UHMWPE) fibers were treated with a coupling agent following the extraction of gel fibers, resulting in modified fibers after subsequent ultra-drawing. The structure and morphology of the modified UHMWPE fibers were characterized and their surface wetting, interfacial adhesion, and mechanical properties were investigated. It was found that the coupling agent was absorbed into the UHMWPE fiber and trapped on the fiber surface. Compared with unmodified UHMWPE fibers, the modified fibers had smaller contact angle, higher crystallinity, and smaller crystal size. The interfacial adhesion and mechanical properties of UHMWPE fibers were significantly improved with increasing coupling agent concentration and gradually reached a plateau value. After treatment with 1.5 wt% solution of a silane coupling agent (γ -aminopropyl triethoxysilane, SCA-KH-550), the interfacial shear strength of the UHMWPE-fiber/epoxy composites was increased by 108% and the tensile strength and modulus of modified UHMWPE fibers were increased by 11% and 37% respectively.     

Effect of Silanes on Mechanical and Thermal Properties of Silicone Rubber/EPDM Blends

The effect of four types of silane coupling agents on the mechanical and thermal properties of silicone rubber and ethylene–propylene–diene monomer (M-class) rubber (EPDM) blends is studied, namely, isobutyltriethoxysilane (BUS), acryloxypropyltriethoxysilane (ACS), aminopropyltriethoxysilane (AMS), and vinyltriethoxysilane (VIS). ACS and VIS increase the crosslink density of the blends, which results in higher tensile strength, modulus, and thermal stability, but lower elongation at break compared with the other silanes. However, the blend containing BUS shows highest tanδ in the temperature range of 45°C to 200°C. Thermogravimetric analysis shows two steps of degradation for all the samples, but little difference with the varied silanes.     

Thermal Properties of Fe-octacarboxyl Acid Phthalocyanine/Polyurethane Blends

The thermal stability of PU has been a critical factor to influence its applications as engineering materials. In this paper, the thermal properties of Fe-octacarboxyl acid phthalocyanine (Fe-OCAP)/polyurethane (PU) blends were investigated. The glass transition temperatures (T_g) of Fe-OCAP/PU blends were analyzed by differential scanning calorimetry (DSC). The results showed that with increasing Fe-OCAP content up to 10% T_g of the samples decreased. Thermal stability of the samples was studied by thermogravimetric analysis (TGA). The decrease of the degradation rate of the samples with increasing Fe-OCAP content indicated an improvement of thermal stability for the modified samples. The activation energy of thermal degradation was calculated by the Freeman and Carroll method. The results showed that the activation energy increased with increasing Fe-OCAP content, which also indicated the improved thermal stability obtained in the modified samples. The thermal properties of the samples were influenced by the incorporation of Fe-OCAP.     

Investigation of the Morphological and Mechanical Properties of Polyethylene Terephthalate (PET)/Ethylene Propylene Diene Rubber (EPDM) Blends in the Presence of Multi-Walled Carbon Nanotubes

In this study the blends of polyethylene terephthalate (PET)/ethylene propylene diene rubber (EPDM) in the presence of multi-walled carbon nanotubes (MWCNT) (1 and 3?wt %) were prepared by melt compounding in an internal mixer. Mechanical and morphological properties of the nanocomposites were investigated. The thermal behaviors of the PET/EPDM nanocomposites were also investigated, by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The results of the mechanical tests showed that the tensile strength, elastic modulus and the hardness of the blends were increased with increasing CNT, while the impact strength and elongation at break decreased. The DSC and TGA results showed an increase of melting temperature (T_m) and degradation temperature of the nanocomposites with the addition of the carbon nanotubes, because the carbon nanotubes serve both as nucleating agents to increase T_m and prevent the composite from degradation to increase the thermal stability. The microstructure of the composites was evaluated through field emission scanning electron microscopy (FESEM) and the results showed a good distribution of the MWCNT within the polymer blend.