Influence of Carbon Nanotubes on the Crystallization and Directional Tensile Behavior of High-Density Polyethylene Prepared by Dynamic-Packing Injection Molding

The influence of multi-walled carbon nanotubes (MWCNTs) on the crystallization and directional tensile properties of high-density polyethylene (HDPE) was studied for samples prepared by dynamic-packing injection molding (DPIM). Oscillatory shear was imposed on the gradually cooled melt during the packing solidification stage of DPIM. For the oriented composites containing 1.8 wt% MWCNTs, the tensile fracture behavior showed typical brittle features along the flow direction (FD) and perpendicular direction (PD), which were almost the same as those that occurred in oriented pure HDPE. The elongation at break along both directions decreased due to the incorporation of MWNCTs in the oriented composites compared with the oriented pure HDPE. However, the tensile strength of the oriented HDPE/MWCNT composites was greatly improved along the FD due to the presence of carbon nanotubes; meanwhile, it was not weakened along the PD. In scanning electron microscopy observations, it was found that there were some oriented hybrid shish-kebab structures in a nanometre scale in the oriented HDPE/MWCNT composites, but not in its isotropic composites. This suggests that MWCNTs were involved in the shear-induced crystallization of HDPE. Differential scanning calorimetry measurements confirmed that the crystallinity of oriented HDPE composites with 1.8 wt% MWCNTs was higher than those of isotropic HDPE and isotropic composites, but was not obviously higher than that of oriented pure HDPE. These findings demonstrate that MWCNTs indeed affected the formation of crystalline structures, but did not greatly influence the crystallinity of HDPE under shear flow. The transition of crystalline morphology might be the reason for change in tensile behavior for the oriented HDPE/MWCNT composites compared with the oriented pure HDPE.     

Studies on HDPE functionalized by ultraviolet irradiation and interfacial interaction of HDPE/STC blend

Compared with ultraviolet irradiation in air, high density polyethylene (HDPE) could be very quickly functionalized by ultraviolet irradiation in ozone atmosphere, introducing oxygen-containing groups such as C=O and C-O onto the molecular chains of HDPE. After ultraviolet irradiation in ozone atmosphere, the molecular weight of HDPE decreased, its distribution became wider, the melt index (MI) increased, and the water contact angle decreased. After irradiating for a short time in ozone atmosphere, the interfacial interaction between the irradiated HDPE and sericite-tridymite-cristobalite (STC) particles is improved. The yield and notched impact strength of the HDPE/STC (60/40) blend with 10 min-irradiated HDPE are increased from 25.5 MPa and 61 J/m for the nonirradiated HDPE/STC (60/40) blend to 30.2 MPa and 360 J/m for the irradiated blend, respectively.     

Investigation on Changes in the Miscibility,Morphology, Rheology and Mechanical Behavior of Melt Processed Cellulose Acetate through Adding Polyethylene Glycol as a Plasticizer

Polyethylene glycol (PEG 200) was used as an eco-friendly plasticizer for preparing thermoplastic cellulose acetate (CA) by a twin-screw extruder. The plasticization efficiency of PEG 200 was compared with that of triethyl citrate (TEC). The interaction between polyethylene glycol and CA was investigated by Fourier transform infrared spectroscopy (FT-IR) and differential scanning calorimetry (DSC). Both FT-IR and DSC proved that PEG 200 could form stable and strong hydrogen bonds with CA molecules. Scanning electron microscopy (SEM) revealed that the CA granules were completely disrupted during the extrusion and a continuous and homogeneous phase was observed. The PEG 200-plasticized cellulose acetate (PCA) showed greater viscosity reduction than TEC-plasticized cellulose acetate (TCA) at the same additive levels. Furthermore, the Izod-notched impact strength and elongation at break of PCA were higher than those of TCA. The tensile strength, Izod-notched impact strength and elongation at break of PCA containing 25 wt% PEG 200 reached 31.6 MPa, 20.9 KJ/m² and 80.5%, respectively, as compared to 39.2 MPa, 10.9 KJ/m² and 32.3% for 25 wt% TEC plasticized CA.     

Thermoplastic Elastomers Based on Ethylene-vinyl Acetate Copolymer and Waste Nitrile Butadiene Rubber Powder Blends Compatibilized by Chlorinated Polyethylene

Thermoplastic elastomers (TPEs) based on ethylene-vinyl acetate (EVA)/waste nitrile butadiene rubber powder (WNBRP) blends compatibilized by chlorinated polyethylene (CPE) were prepared by melt-compounding. The tensile strength and the elongation at break of the EVA/CPE/WNBRP blends were increased significantly compared with those of the EVA/WNBRP blends. The fracture surfaces of the EVA/CPE/WNBRP blends were smooth; moreover, the WNBRP in the etched EVA/CPE/WNBRP blends were inserted in the EVA matrix tightly. DMA results revealed that when the CPE dosage was 5 phr in the EVA/CPE/WNBRP blend, the Payne effect was weakened significantly.     

Effects of Blend Ratio on Rheology,Morphology, Mechanical and Oil-Resistant Properties in Chlorinated Polyethylene Rubber and Copolyamide Blends

The elastomeric chlorinated polyethylene (CPE) blended with a low melting point copolyamide (PA6/PA66/PA1010, PA) was prepared by a melt mixing technique. The mixing characteristics of the blends were analyzed from the rheographs. The influence of copolyamide (PA) content on the morphology, mechanical properties, crystallization and oil-resistance, and the addition of compatibilizers on the mechanical properties were also systematically investigated. Morphological examinations clearly revealed a two-phase system in which CPE/PA blends exhibit a cocontinuous morphology for 50/50 composition, and the continuous phase of PA turns into a disperse phase for 70/30, 80/20, and 90/10. There is a distinct interface between the two phases. The mechanical properties, crystallization, and oil-resistance have a strong dependence on the amount of PA. The blends with higher proportions of PA have superior mechanical properties; they are explained on the basis of the morphology of the blend and the cystallinity of PA. In addition, compatibilizers, including chlorinated polyethylene-graft-copolyamide (CPE-G-PA), chlorinated polyethylene-graft-maleic anhydride (CPE-G-MAH), ethylene-n-butyl acrylate-monoxide (EnBACO), and ethylene-n-butyl acrylate-monoxide-graft-maleic anhydride (EnBACO-g-MAH) were added into the blends. Tensile strength and elongation at break go through a maximum value at a compatibilizer resin content (on the basis of the total mass of the blend) of 20 wt% while the PA content is 30 wt%.     

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.     

Preparation and Mechanical and Tribological Properties of High-Density Polyethylene/Hydroxyapatite Nanocomposites

High-density polyethylene (HDPE) nanocomposites reinforced with hydroxyapatite nanorods (nHA) were fabricated by means of extrusion and injection molding. The thermal, mechanical, and dry sliding wear properties of HDPE-based nanocomposites filled with nHA loadings up to 20 wt% were investigated. The results of mechanical property characterization showed that nHA additions improved the hardness, elastic modulus, and yield strength of HDPE at the expense of its tensile ductility and impact strength. Thermogravimetric analysis and heat deflection temperature measurements revealed that nHA fillers are very effective to enhance the thermal stability of HDPE. The wear behavior of HDPE/nHA nanocomposites was studied using a pin-on-disk tribometer. nHA fillers of a large aspect ratio improved the wear resistance of HDPE substantially because of their load-bearing effect and the formation of a continuous transfer film on the steel counterface.     

Morphology and mechanical properties of PP/HMWPE blends

Mechanical properties and morphology of blends of polypropylene (PP) with high molecular weight polyethylene (HMWPE) prepared by coprecipitation from xylene solution are investigated. Compared to blends of PP with commercial high-density polyethylene (HDPE), the mechanical properties of the blends of PP/HMWPE are much superior to those of PP/HDPE blends. Not only is the tensile strength stronger, but also the elongation at break is much higher than that of the PP/HDPE blends of the same composition. These differences increase with increasing HMWPE and HDPE content. Scanning electron microscopy of the fracture surface resulting from the tensile tests shows that the compatibility in PP/ HMWPE blends is much better than that in PP/HDPE blends. This is most likely attributable to the enhanced chain entanglement of HMWPE with the PP in the amorphous phase due to the lower crystallinity, owing to the high molecular weight of the HMWPE, and a much more flexible chain. The thermal behavior and spherulite morphology of both blends are also investigated.     

The Enhanced Melt Intercalation of Polyethylene Using Exothermal Montmorillonite

Exothermal montmorillonite (EMMT) was prepared and used in the preparation of HDPE composites in which the EMMT was intercalated. Compared with the ODA modified montmorillonite (OMMT), EMMT exhibited better intercalation behavior during melt compounding, resulting in similar tensile modulus and better tensile strength and elongation at break of the corresponding composites. The crystallization of the polymeric matrix and the dispersion of MMT were systemically investigated; their relationship with the mechanical properties of the composites are discussed as well.     

Mechanical and Thermal Performance of High-Density Polyethylene/Alumina Nanocomposites

High-density polyethylene (HDPE) nanocomposites reinforced with pristine and vinyltrimethoxysilane (VTMS)-treated alumina nanoparticles of 2, 4, and 6 wt% were melt-compounded in a twin-screw extruder followed by injection molding. Their structure, thermal and mechanical behaviors were studied. Fourier transform infrared (FTIR) spectra showed that VTMS was successfully covalently grafted to the alumina nanoparticles. The X-ray diffraction (XRD) patterns indicated that the alumina nanoparticle additions broadened the characteristic peak width of HDPE, indicating that they reduced the crystallite size of HDPE. The heat deflection temperature and thermogravimetric analyses demonstrated that the dimensional and thermal stability of HDPE were enhanced markedly by adding pristine and silane-treated alumina nanoparticles. The alumina nanoparticle additions were also beneficial in enhancing Young's modulus and yield strength of HDPE. The reinforcing effect was particularly apparent in the silane-treated nanocomposites due to improved filler–matrix interactions.     

Influence of High-Density Polyethylene and Nano-Calcium Carbonate of Various Content Ratios on the Crystallization of Polypropylene

The influence of high-density polyethylene (HDPE) and nano-CaCO₃ of various content ratios on the crystallization of polypropylene (PP) was investigated by differential scanning calorimetry, dynamic rheology, wide angle X-ray diffraction (WAXD), and Izod impact strength measurements. The results showed that HDPE and PP were phase separated in their blends and the additive CaCO₃ filler mainly dispersed in the PP phase, acting as a nucleation agent to promote the crystallization of PP. For the samples HDPE/ nano-CaCO₃ 30/0 and 25/5, the β crystals content was much higher than the other samples. The reason is that the viscosity difference between HDPE and PP led to a velocity difference, which could induce shear stress at the interfaces of HDPE and PP during injection molding. The intensive shear stress at their phase interfaces is advantageous for orientation of the chains, inducing the formation of β crystals. However, with the increment of CaCO₃ content, there were dual effects of CaCO₃ on the crystallization of PP: at low CaCO₃ content, it would hamper the orientation of PP chains, thus leading to a decrease of β crystals; at high CaCO₃ content, it would induce β crystals by itself.     

Study on Properties and Structure of Near Melt Point Extruded High‐Density Polyethylene

The effect of extrusion temperature on the mechanical properties of high‐density polyethylene (HDPE) was examined using solid‐state extrusion (SSE) and melt‐state extrusion (MSE) techniques. Differential scanning calorimetry (DSC) and scanning electron microscopy (SEM) investigations were employed to provide evidence for explaining the relationship between mechanical properties and morphology of extrusion moldings. Extruded from a convergence‐divergence die, compared with samples obtained by MSE, the yield strength of samples obtained by SSE was enhanced in both longitudinal and transverse directions with a ductile failure. The yield strength decreased sharply with increasing extrusion temperature. The maximum longitudinal yield strength of samples extruded at 112°C was 181 MPa with an 87% elongation at break; the corresponding values were 28 MPa and 800% for samples extruded at 140°C (MSE); in the transverse direction the yield strength was 27 MPa with a 101% elongation at break for samples extruded at 140°C, while the maximum yield strength was 51 MPa with a 45% of elongation at break for samples extruded at 116°C. Compared with sheets extruded at 140°C, DSC data shows a 5.3°C increase in melting point, a 9.5°C decrease in melt point width, and a 7.1% decrease in crystallinity for sheets extruded at 112°C. SEM indicates that spherulites predominate in MSE samples, while a preferred orientation of the lamellae along the extrusion direction were mainly produced by SSE.     

Improvement of Mechanical Properties and Ultraviolet Resistance of Polyethylene Pipe Materials Using High Density Polyethylene Matrix Grafted Carbon Black

In recent years, high grade high density polyethylene (HDPE) pipe materials are being more and more widely used for water and gas supply. Carbon black (CB) is usually used as an anti-UV-light reagent for pipe materials. However, homogeneous dispersion of CB in the HDPE matrix and modification of the interface has always been a great challenge. In this work, HDPE matrix grafted CB (HDPE-g-CB) was successfully prepared through HDPE radicals formation by a thermo-mechanical method and subsequent radical capture by the CB surface. The weight percentage of grafted HDPE approached 10 wt% and the modification sharply reduced the surface free energy of the CB. The SEM (scanning electron micrographs) and TEM (transmission electron microscopy) results showed that HDPE-g-CB was uniformly dispersed in the HDPE pipe materials and the domain size of the dispersed phase was remarkably decreased from that in HDPE/CB. Therefore, compared with the HDPE/CB, the mechanical properties and ultraviolet (UV) resistance of HDPE/HDPE-g-CB were significantly improved, positively influencing the expected life span of pipelines.     

Biaxially Self-Reinforced High-Density Polyethylene Prepared by Vibration-Assisted Injection Molding. I. Processing Conditions and Physical Properties

A pulse pressure was imposed on the melt in the injection molding cavity during the injection and holding pressure stages, called vibration-assisted injection molding (VAIM) technology. With the VAIM technology, biaxially self-reinforced high-density polyethylene (HDPE) samples were prepared and the physical properties affected by the vibration processing conditions were studied. The tensile properties can be improved in both the machine direction (MD) and the transverse direction (TD) by changing the vibration frequency and vibration pressure amplitude, respectively. The elongation at break increased with increasing the vibration frequency for the VAIM sample processed at constant low vibration pressure amplitude; the yield strength increased with increasing the vibration pressure amplitude for the VAIM sample prepared at constant low vibration frequency. The softening point temperature for the VAIM sample increased by 8°C compared with a conventional injection-molded (CIM) sample.     

Preparation,Characterization, and Properties of Pre-irradiated Linear Low-Density Polyethylene Grafted Itaconic Anhydride by Reactive Extrusion

Graft copolymerization of itaconic anhydride (IAH) onto pre-irradiated linear low-density polyethylene (LLDPE) was carried out in a twin-screw extruder. FT-IR was used to characterize the formation of graft copolymer and the percentage of grafted IAH was determined. The effects of monomer concentration and screw speed on degree of grafting were studied. The thermal behavior of LLDPE-g-IAH was investigated using differential scanning calorimetry. The crystallization temperature (T_c) of LLDPE-g-IAH increased compared of that of neat LLDPE. The tensile properties of the graft copolymer were determined. No obvious changes could be found for the tensile strength, elongation at break, and Young's modulus of the graft copolymer compared to that of neat LLDPE. It was found that contact angles of the water on the film surface of LLDPE-g-IAH decreased with increasing content of IAH in LLDPE-g-IAH. Adhesion between the graft copolymer and stainless steel was investigated. Outstanding peel strength was obtained by introducing polar groups onto the LLDPE molecular chains.     

Tribological Properties of Polycarbonate Blended with High‐density Polyethylene and High‐density Polyethylene Grafted with Maleic Anhydride

High‐density polyethylene (HDPE) and maleic anhydride grafted HDPE (HDPE‐g‐MA) were selected as lubricant and compatibilizer, respectively, for improving the tribological and mechanical properties of polycarbonate (PC). The morphology of worn surfaces and debris was observed by means of scanning electron microscopy (SEM). The mated steel ring surface was analyzed by using SEM combined with energy dispersive spectroscopy (EDS). Both HDPE and HDPE‐g‐MA reduced the friction and wear of pure PC. HDPE‐g‐MA, which had a better compatibility with PC than HDPE, resulted in better improvement of the mechanical and tribological properties of the PC matrix. A 10 vol. % HDPE‐g‐MA reduced the wear of pure PC by 4 orders of magnitude, and the friction coefficient was reduced from 0.86 to 0.22. Such improvements in the tribological behavior resulted from the good self lubrication of HDPE and HDPE‐g‐MA. The PC/HDPE‐g‐MA (S_90‐0‐10) polyblend also showed higher notched impact strength than pure PC. It may be a useful material for application in tribological fields.     

Effect of Polyethylene Functionalization on Mechanical Properties and Morphology of PE/SiO2 Composites

In this study composites of high density polyethylene (HDPE) with various SiO₂ content were prepared by melt compounding using maleic anhydride grafted polyethylene (PE-g-MAH) as a compatibilizer. The composites containing 2, 4 and 6% by weight of SiO₂ particles were melt-blended in a co-rotating twin screw extruder. In all composites, polyethylene-graft-maleic anhydride copolymer (PE-g-MAH, with 0.85% maleic anhydride content) was added as a compatibilizer in the amount of 2% by weight. Morphology of inorganic silica filler precipitated from emulsion media was investigated. Mechanical properties and composite microstructure were determined by tensile tests and scanning electron microscopy technique (SEM). Tensile strength, yield stress, Young's modulus and elongation at break of PE/SiO₂ composites were mainly discussed against the properties of PE/PE-g-MAH/SiO₂ composites. The most pronounced increase in mechanical parameters was observed in Young's modulus for composites with polyethylene grafted with maleic anhydride. The increase in the E-modulus of PE/PE-g-MAH/SiO₂composites was associated with the compatibility and improvement of interfacial adhesion between the polyethylene matrix and the nanoparticles, leading to an increased degree of particle dispersion. This finding was verified on the basis of SEM micrographs for composites of PE/PE-g-MAH/4% by weight of SiO₂. The micrographs clearly documented that addition of only 2 wt% of the compatibilizer changed the composite morphology by reducing filler aggregates size as well as their number. Increased adhesion between the PE matrix and SiO₂ particles was interpreted to be a result of interactions taking place between the polar groups of maleic anhydride and silanol groups on the silica surface. These interactions are responsible for reduction of the size of silica aggregates, leading to improved mechanical properties.     

Non-isothermal crystallization kinetics of alkyl-functionalized graphene oxide/high-density polyethylene nanocomposites

Dodecyl amine-functionalized graphene oxide (DA-GO) was obtained via an amidation reaction. The results of X-ray diffraction and Fourier-transform infrared spectroscopy verified that long alkyl chains of DA were successfully grafted on the GO sheets. Transmission electron microscope and scanning electron microscope techniques illustrated that homogeneously dispersed DA-GO/high-density polyethylene (HDPE) nanocomposites were obtained. The effects of DA-GO on the non-isothermal crystallization of HDPE were then investigated by differential scanning calorimetry (DSC) at various cooling rates (2, 5, 10, and 20?°C/min). Significant increase in the onset crystalline temperature (T_o) and the peak crystallization temperature (T_p) of HDPE incorporating DA-GO indicated the strong nucleating ability of DA-GO. The investigation of half-time crystallization time (t_1/2) demonstrated that crystallization rate of HDPE consisting of DA-GO is faster than that of pure HDPE at a given cooling rate. Ozawa, Avrami, and the combined Avrami–Ozawa methods (Mo) were used for analyzing experimental data. The Mo approach was successful in describing the non-isothermal crystallization process of DA-GO/HDPE nanocomposites. The results indicated that low DA-GO content accelerates the crystallization of HDPE, while higher content hinders the crystallization of HDPE.     

The Effect of Poly(Ethylene Succinate) on Mechanical Properties of PLLA/PES Blend Prepared by Melt-Blending

Fully biodegradable poly(L-lactide) and poly(ethylene succinate) (PLLA/PES) blends were prepared via melt-blending using PLLA and PES as reactants in a stainless steel chamber. The prepared PLLA/PES blend, as well as neat PLLA and PES, was characterized by Fourier transform infrared spectra (FTIR) and X-ray diffraction (XRD) to confirm the structure and the crystallization of PLLA in the blend. The mechanical properties of PLLA/PES blends were determined by bending and tensile tests and the effects of PES content on the mechanical properties of PLLA/PES blends were investigated. It was found that blending some amount of PES could significantly improve the elongation at break while still keeping considerably high strength and modulus. With increasing PES content, both strength and modulus gradually decreased; however the elongation at break significantly increased. SEM was used to examine the morphology of fracture surfaces of PLLA/PES blends.     

Composites Based on Polyethylene and Keratin Hydrolysates

Novel composites based on polyethylene ELITE? 5230GC and keratin hydrolysates (amino acid composition, dipeptide, tetrapeptide) have been first developed and studied. It has been shown that the introduction of keratin hydrolysates leads to an increase in the elastic modulus E₀ of the composites compared with the E₀ value of the matrix and a decrease in their tensile strength and elongation at break. It has been found that the water content in keratin hydrolysates is 3–4%. The differential scanning calorimetry curves of keratin hydrolysates exhibit a broad peak during the first heating and no peaks during the second heating of keratin hydrolysates. The temperature corresponding to the minimum of the broad peak observed during the first heating is shifted to low temperatures: from 99.1 to 82.5°C. In this case, the peak area varies from 109.3 J/g for the amino acid composition and 104.0 J/g for dipeptide to 140.8 J/g for tetrapeptide. During the second heating, the peak temperatures for the composites decrease compared with the peak temperature for polyethylene. The enthalpy of the composites also decreases compared with the enthalpy of the matrix.