Correlation of Oscillation Cycles and Crystallization in HDPE Blends with Small Amounts of HMWPE Prepared by Dynamic-Packing Injection Molding

The effect of oscillation cycles on crystal morphology was investigated for high-density polyethylene (HDPE) in blends with 4 wt% high molecular weight polyethylene (HMWPE) (labeled B4) in samples prepared through dynamic-packing injection molding (DPIM). With the aid of differential scanning calorimetry (DSC), scanning electron microscopy (SEM), and transmission electron microscopy (TEM), a weblike shish-kebab morphology that markedly increased stiffness and toughness was found at a specific oscillation cycle. The DSC and SEM results showed that crystal morphology was altered with changes in the oscillation cycle. The SEM and TEM results showed that a much better weblike shish-kebab structure, in which most of the lamellae connect different columns compared with conventional shish-kebabs, was formed in the B4 samples when the oscillation cycle was 10s. These results show that a proper oscillation cycle favors the improvement of crystal structures in HDPE blends induced by a small amount of HMWPE.     

Mechanical Properties and Morphology of LDPE/PP Blends

Two types of polypropylene (PP) with different molecular structure, namely, homogeneous PP (PPH) and PP block‐copolymer (PPC), were blended with a long chain, branched, low density polyethylene (LDPE) in a twin screw extruder and then injection moulded into test specimens; the mechanical properties and morphology of the blends are reported. The tensile strength, elastic modulus, flexural strength, and flexural modulus of the blends increased monotonically with increasing PP content, although exhibiting a slightly negative deviation from the rules of mixtures due to the relatively poor compatibility of the components, which caused the blends to separate into individual phases. Comparatively, these mechanical properties of the LDPE/PPH blend were much higher than that of the LDPE/PPC blend, which was attributable mainly to the fact that the mechanical properties of neat PPH are stronger than that of neat PPC. With respect to the impact strength of the blends, a maximum value appeared in LDPE/PPH blends when PPH content was about 20% and also in LDPE/PPC blends when PPC content was about 40%.     

Morphologies and Mechanical Properties of High-Density Polyethylene Induced by the Addition of Small Amounts of Both Low- and High-Molecular-Weight Polyolefin under Shear Stress Applied by Dynamic Packing Injection Molding

This paper focuses on the mechanical properties and crystal morphology of a self-reinforced high-density polyethylene 5000S (HDPE 5000S) by simultaneously blending with 9 wt% high-molecular-weight polyethylene (HMWPE) and 9 wt% low-molecular-weight polyethylene (LMWPE) (A9) under the shear stress field which was engendered by a self-made dynamic packing injection molding (DPIM) machine. The results of mechanical properties, differential scanning calorimetry, and scanning electron microscopy characterization were as follows: (1) The tensile strength of the dynamic samples increased to 112.1 MPa, 4.85 times as much as that of static packing injection molding (SPIM) samples (23.1 MPa), as a result of realizing polyethylene's self-enhancement; (2) Shish-kebab structure was found in the dynamic samples; (3) The crystallinity of the DPIM A9 sample reached 68.6%, on increase by 18.7% compared with that of the SPIM sample. The formation of the shish-kebab structure and enhancement of mechanical properties are explained.     

Dynamic Rheological Behavior of HDPE/UHMWPE Blends

The rheological behaviors of high-density polyethylene (HDPE)/ultra-high molecular weight polyethylene (UHMWPE) blends prepared by melt blending and solution blending were studied. The results showed that the rheological parameters (G′, G ^″, and η*) of both types of blends increased gradually with increasing fraction of UHMWPE, while the tanδ decreased correspondingly. Comparing blends with the same UHMWPE content, all G′, G ^″, and η* values of solution blends were higher, and the tanδ of the solution blends were remarkably lower than those of the melt blends. Combined with the scanning electron microscopy (SEM) observations, it was proved that, because of its very high melt viscosity, the UHMWPE chain is difficult to diffuse and be distributed well in the HDPE matrix by melt blending, resulting in a two-phase-like morphology. On the other hand, the blends prepared by the solution blending showed a homogeneous distribution of UHMWPE in the HDPE matrix. In addition, the state of aggregation of the UHMWPE in the HDPE matrix can be distinguished well by time–temperature superposition (TTS) curves; i.e., the two-phase-like morphology in the melt blends can be detected by the failure of TTS in the high-frequency range, which cannot be reflected by Cole–Cole plots and Han curves.     

Effects of Addition of Ultra-High Molecular Weight Polyethylene on Tie-Molecule and Crystallization Behavior of Unimodal PE-100 Pipe Materials

With the fast-growing global market demand for high-grade plastic pipe materials, high-density polyethylene (HDPE) products, such as PE-100, are playing a more and more important role. On the other hand, lack of basic understanding about these materials hinders the further development of this field. To investigate the effects of addition of an ultra-high molecular weight polyethylene (UHMWPE) on tie-molecules, crystallization kinetics and long-term properties of a unimodal HDPE pipe material (UMPE-100) made from a Cr-based catalyst, the blends of UMPE-100/UHMWPE were prepared through a twin-screw extruder. The probability of tie-molecules was calculated by a statistical approach, which has been proposed by Huang and Brown (Huang, Y.L.; Brown, N.J. Polym. Sci. B. 1991, 29, 129–137). It showed that as UHMWPE was added, the probability of tie-molecules increased due to increased molecular weight. The crystallization kinetics of the blends was investigated by an isothermal crystallization method using differential scanning calorimetry. Addition of small amount of UHMWPE improved the crystallization rate greatly. The natural draw ratio of blends decreased with improvement of tie-molecule probability and crystallization rate, indicating improvement in long-term properties.     

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.     

CORRELATION AMONG MORPHOLOGY,INTERFACE, AND MECHANICAL PROPERTIES: EXPERIMENTAL STUDY

The effect of the disperse phase and the diffuse interface between phases on the tensile and impact strengths of polypropylene (PP)/poly(ethylene terephthalate) (PET) (75/20 by weight) blends compatibilized with maleic anhydride–grafted PP derivatives and on the tensile modulus of poly(vinyl chloride)/polystyrene (PVC/PS) nanoparticle blends compatibilized with polystyrene/poly(vinyl acetate) (PS/PVAc) block copolymers were investigated experimentally. The weight fraction of the diffuse interface between the PP and PET phases in the PP/PET blends was determined by modulated differential scanning calorimetry (MDSC). A correlation between the diffuse interface content and mechanical properties was found. With increasing diffuse interface weight fraction, the impact and tensile strengths of the PP/PET blends increased. There is a brittle-tough type transition in these PP/PET blends. With increasing diffuse interface content in the PVC/PS nanoparticle blends in which the particle size was fixed at about 100 nm, the tensile modulus also clearly increased.     

Morphology-property relationships in polycarbonate-based blends. I. Modulus

The tensile, dynamic mechanical and morphological properties of PC/HDPE, PC/LDPE and PC/PS blends have been investigated with the intent of clarifying the major factors governing the modulus of these essentially incompatible blends. Scanning electron microscopy shows that all of the PC/HDPE, PC/LDPE and PC/PS blends have a domain structure whose morphology is strongly dependent on the concentration of the dispersed phase; when the dispersed phase concentration is less than 15%, the domains are mostly of spherical shape, while above 20% agglomeration takes place to form rodlike structures. Dynamic mechanical data shows there is essentially no adhesion at the PC-HDPE and PC-LDPE boundaries, while there is appreciable adhesion at the PC-PS interface. The existence of an intermixed zone was postulated to explain this interfacial adhesion. Morphological and thermal analysis results also indicate that both the HDPE and LDPE inclusions are loosely sitting in the holes in the PC matrix while the PS inclusions are compactly embedded in the PC matrix. These differences in boundary nature give marked effects on the tensile properties including the modulus. For the modulus, PC/HDPE and PC/LDPE blend systems can be regarded to be mechanically equivalent to a PC matrix alone with holes in it when the dispersed phase concentration is lower than 15%, while in the case of PC/PS blends the PS inclusions contribute substantially to the sample's overall modulus.     

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.     

Mechanical,Thermal, and Surface Properties of Ultrahigh Molecular Weight Polyethylene/Polypropylene Blends

Various compositions of ultrahigh molecular weight polyethylene/polypropylene (UHMWPE/PP) blends were prepared in decalin, with the rheological, mechanical, thermal, and surface properties of the blends being determined using the solution cast film. Viscosity and mechanical properties of the blends decreased below the additivity value with increasing PP content implying that PP molecules disturb the entanglement of UHMWPE. Contact angle of the blend films with a water drop increased with increasing content of PP. The atomic force microscope (AFM) images showed that the surface of cast UHMWPE was very smooth whereas that of cast PP was very uneven. For blends, the surface became rough and uneven with increasing content of PP. The melting temperature of PP (T _mP) decreased in the blends with increasing UHMWPE content while that of UHMWPE (T _mU) remained almost constant in blends.     

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.     

Improvement of the mechanical and rheological properties of HDPE/PET/MWCNT nanocomposites

High density polyethylene (HDPE)/poly (ethylene terephthalate) (PET) (90/10 wt.%) blends and HDPE/PET/multi-walled carbon nanotubes (MWCNTs) nanocomposites were prepared by melt mixing process, and the influence of MWCNTs on the mechanical and rheological properties of the nanocomposites was investigated. MWCNTs were added up to 5 wt.% in the HDPE/PET matrix. Transmission electron microscopy images reveal that the MWCNTs were homogeneously dispersed in the HDPE/PET matrix. Improvement of mechanical properties was observed by the addition of MWCNTs compared with HDPE/PET blends. Prominent increases in the complex viscosity and storage modulus of the nanocomposites were found with increasing MWCNT content.     

Effects of electron-beam irradiation on surface oxidation of polymer composites

The aim of this article was to show the effects of an electron radiation dose and presence of a compatibilizer on the oxidation of composites made of blends of low-density polyethylene (LDPE), high-density polyethylene (HDPE), polypropylene (PP), polystyrene (PS), and poly(ethylene terephthalate) (PET) as well as of blends of LDPE, HDPE, and PP. As the compatibilizers, the styrene-ethylene/butylene-styrene elastomer grafted with maleic anhydride (SEBS-g-MA) and trimethylol propane trimethylacrylate (TMPTA) were used; they were added in the amounts of 5, 10, and 15 wt% and 1, 2, and 3 wt%, respectively. The oxidation of the surface layer (SL) was investigated by the X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR). It was found that the extent of the composite oxidation increased with the increasing dose of the electron radiation. The addition of the compatibilizers enhanced the oxidation of the SL but hindered the oxidation of the bulk of the material.     

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.     

Studies on Rheological Behavior and Structure Development of High‐Density Polyethylene in the Presence of Ultrasonic Oscillations During Extrusion

The effects of ultrasonic oscillations on properties and structure of extruded high‐density polyethylene (HDPE) were studied. The experimental results show that ultrasonic oscillations can improve the surface appearance of the HDPE extrudates; increase the productivity of the HDPE extrudates; and decrease the die pressure, melt viscosity, and flow activation energy of the HDPE. The processing properties of the HDPE improve greatly in the presence of ultrasonic oscillations. Linear viscoelastic properties tests show that dynamic shear viscosity and zero shear viscosity decrease in the presence of ultrasonic oscillations. Ultrasonic oscillations can improve crystal perfection and thermal stability of HDPE. At appropriate ultrasound intensity, ultrasonic oscillations could also increase the mechanical strength of extruded HDPE. The gel permeation chromatography (GPC) results show that at high ultrasound intensity and low rotation speed of extrusion, ultrasonic oscillations causes chain scission of HDPE, which result in a decrease of molecular weight and an increase of melt flow index.     

Activation Energy for the Glass Transition of a Confined Elastomer in HDPE/PP Blends

Blends of two highly crystalline polymers containing an elastomer were prepared to study the glass transition of the confined elastomer. The polymers chosen were high density poly ethylene (HDPE), polypropylene (PP), and two elastomers of a different nature: natural number (NR) and EPDM. The dynamic mechanical analyzer (DMA) technique was used to analyze the storage modulus of blends with elastomer content from 0% to 30% by weight, with the remainder made up of equal amounts of HDPE and PP, and blends with 10% of the elastomer, but varied ratios of polyolefins. We used the differentiation modification of the Arrhenius method in the kinetic analysis assuming an n‐order relaxation mechanism, which allowed detecting the percolation threshold of NR. Results indicate that both temperature and activation energy for glass transition (T _g ) are dependent on the types of polymers in the blend and blend composition. The T _g and E values of the unblended elastomers are higher than those in blends; this behavior is associated with the elastomer confinement and blend morphology.     

Adhesion enhancement in polystyrene/polyethylene blends by corona treatment and triblock copolymer addition

A comparative study of interfacial effects due to styrene-butadiene-based triblock copolymer (SEBS) addition and to corona treatment has been investigated for blends of polyethylene (PE) and polystyrene (PS). Blends of PS/PE covering a wide range of weight composition have been prepared in the molten state. Scanning electron microscopy demonstrated that moderate amounts of SEBS copolymer addition (2-5%) resulted in finer particle dispersion and in better interfacial adhesion between PE and PS phases. Tensile strength and elongation at break were also significantly improved. In the case of corona treatment of both polyethylene and polystyrene, the tensile strength of the blends increased while their elongation at break remained almost unchanged. The same trend was found when small amounts of corona-treated blend (5%) were added to the non-modified PS/PE blends. Rheological measurements revealed that corona treatment resulted in a decrease of dynamic shear viscosity of both PE and PS. From a view-point of morphological and mechanical properties, the triblock copolymer was found to be the more efficient modifier. Nevertheless, much higher tensile strengths, but lower elongations at break were obtained when the blends were modified by corona-treated SEBS copolymer. The results suggest that a combination of the two modification methods may be a promising route to enhance performance properties in the immiscible PS/PE system.     

衰减全反射红外光谱法的高密度聚乙烯自然老化特性研究

采用衰减全反射红外光谱技术(ATR-FTIR)研究物资储备中广泛使用的滚塑包装箱专用高密度聚乙烯(HDPE),在特定湿热海洋环境的海南万宁实验站1年期内自然老化特性。定性分析老化前后化学结构变化,从断链、支化以及氧化角度区分不同阶段的老化特性,根据特征峰峰强和峰面积变化,定量分析羰基指数和相对结晶度的变化规律,探索老化前后羰基指数、相对结晶度变化与力学性能变化的相关性。结果表明：老化行为三个月内以断裂、支化为主,3~6个月氧化逐渐产生,6个月后氧化和支化占主导地位,9个月后氧化程度逐渐饱和,且老化进程与温度和辐照正相关。12个月后,羰基指数增长112倍,结晶度上升约10%,力学性能中材料拉伸/弯曲模量较拉伸/弯曲强度下降更快。老化前后羰基指数与拉伸模量变化相关系数为0.97,基于720~730 cm-1特征谱带计算的相对结晶度变化与拉伸强度变化相关系数为0.96。结果表明采用ATR-FTIR可以在快速无损检测的前提下,从老化前后化学结构的变化推测力学性能的变化。     

The Effect of Benzoyl Peroxide and Divinyl Benzene on the Properties of Cross-Linked Recycled Polyolefin Blends

The effect of peroxide cross-linking on the properties and morphology of recycled polyethylene (PE)/polypropylene (PP) blends was characterized. The addition of benzoyl peroxide (BPO) decreased the melt flow rate (MFR) and increased the impact strength of the recycled polymer blends. Divinyl benzene (DVB) is often used as a cross-linking agent assistant. Compared with BPO modification, the addition of BPO together with DVB improved the cross-linking efficiency and further increased the impact strength of the recycled polymer blends. The effect of BPO content on the MFR and the mechanical properties was also studied with the DVB content fixed. However, chemical cross-linking slightly reduced the thermal stability of the polymer blends. The morphology of the modified and unmodified polymer blends showed that with the addition of BPO, with or without DVB, the compatibility of the PE/PP blends was improved, resulting in enhanced impact strength.     

Comparison of Mechanical Properties and Rheological Behavior of Trans-Polyisoprene/Polypropylene and Ethylene Propylene Diene Rubber/Polypropylene Thermoplastic Vulcanizates

The degree of dynamic vulcanization, mechanical properties, rheological behavior, and the ageing-resistant performance of trans 1,4-polyisoprene (TPI)/polypropylene (PP) and ethylene propylene diene rubber (EPDM)/PP thermoplastic vulcanizates with a blend ratio of 60/40 were investigated comparatively. The results showed that TPI had fully dynamically vulcanized when mixed with PP in the Hakke mixer chamber (175°C, 60 rpm) while EPDM had only partly dynamically vulcanized due to its saturated main chain backbone. With increased sulfur content, the torque at the end of the curing curves of the two thermoplastic vulcanizates (TPVs) increased in the curing characteristics measuring process as the degree of crosslinking increased. Comparing the two blends, TPI/PP-TPVs were possessed of a better mobility, a little lower tensile strength and tear strength, a little higher 100% modulus and hardness, and much lower elongation at break. EPDM/PP-TPVs had better ageing-resistant characteristics due to EPDM's saturated main chain backbone.