超高相对分子质量聚乙烯对双峰HDPE树脂性能的影响

为了提高双峰高密度聚乙烯（HDPE）的力学性能,采用超高相对分子质量聚乙烯（UHM—WPE）与双峰HDPE以不同比例共混,对共混物的相对分子质量及其分布、热性能、流变性能和力学性能进行了测试。UHMWPE的加入使高相对分子质量部分显著增加,流变性能下降,添加量小于10％（质量分数）时,共混物粘度在高剪切速率下变化不大;UHMWPE可提高共混物的熔融温度和初始结晶温度,结晶度先增加然后迅速降低;随着UHMWPE含量的增加,混合物的拉伸强度也随之增加,呈线性关系;结晶度与冲击强度成反比。     

Binary and ternary particulated composites: UHMWPE/CACO3/HDPE

A study of the influence of employing ultrahigh molecular weight polyethylene (UHMWPE) on the toughness of CaCO₃/high‐density polyethylene (HDPE) composites was carried out. Binary and ternary HDPE‐based composites with calcium carbonate in the range of 0–40% and UHMWPE in the range of 0–50% were produced by twin‐screw extrusion followed by compression molding. From tensile and impact tests, it was found that increasing calcium carbonate content increased tensile modulus, but decreased tensile strength, strain at break, and impact resistance. The addition of UHMWPE helped to increase the strain at break and impact resistance of composites moderately without decreasing modulus or strength. The degree of toughening was found to increase with increasing UHMWPE content, but to decrease as the filler volume fraction was increased. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 1503–1513, 2000     

Processing–Nanostructure–Property Relationships of All‐Polyethylene Composites Reinforced by Flow‐Induced Oriented Crystallization of UHMWPE

All‐polyethylene composites exhibiting substantially improved toughness/stiffness balance are readily produced during conventional injection molding of high density polyethylene (HDPE) in the presence of bimodal polyethylene reactor blends (RB40) containing 40 wt% ultrahigh molar mass polyethylene (UHMWPE) dispersed in HDPE wax. Scanning electron microscopy (SEM) and differential scanning calorimetry (DSC) analyses shows that flow‐induced crystallization affords extended‐chain UHMWPE nanofibers forming shish which nucleates HDPE crystallization producing shish‐kebab structures as reinforcing phases. This is unparalleled by melt compounding micron‐sized UHMWPE. Injection molding of HDPE with 30 wt% RB40 at 165 °C affords thermoplastic all‐PE composites (12 wt% UHMWPE), improved Young's modulus of 3400 MPa, tensile strength of 140 MPa, and impact resistance of 22.0 kJ/m². According to fracture surface analysis, the formation of skin‐intermediate‐core structures accounts for significantly improved impact resistance. At constant RB40 content both morphology and mechanical properties strongly depend upon processing temperature. Upon increasing processing temperature from 165 °C to 250 °C the average shish‐kebab diameter increases from the nanometer to micron range, paralleled by massive loss of self‐reinforcement above 200 °C. The absence of shish‐kebab structure at 250 °C is attributed to relaxation of polymer chains and stretch‐coil transition impairing shish formation.     

High density polyethylene/ultra high molecular weight polyethylene blend. II. Effect of hydroxyapatite on processing,thermal, and mechanical properties

Hydroxyapatite (HA) is part of bone mineral composition. Several attempts have been made to incorporate HA into high density polyethylene (HDPE) to produce bone replacement biomaterials since neat HDPE is not suitable as bone replacement. The blending of HDPE with ultra high molecular weight polyethylene (UHMWPE) up to 50% by weight was performed with the aim of improving the toughness of composites. Reinforcement of blend with HA of up to 50% by weight was carried out. Methods of characterizing the composites included density, differential scanning calorimetry, thermal gravimetric analysis, ash content, and morphological examination using scanning electron microscope. For the mechanical properties of the composites, tensile, flexural, and impact tests were carried out. Incorporation of HA into HDPE has resulted in the brittleness of the composites. Blending of HDPE with UHMWPE in the presence of HA was found to improve the mechanical properties and promote a ductile failure of the resulting composites. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 3931–3942, 2006     

Properties of bamboo flour/high-density polyethylene composites reinforced with ultrahigh molecular weight polyethylene

In order to improve the properties of bamboo-plastic composites (BPCs), bamboo flour/high-density polyethylene (HDPE) composites were reinforced with ultrahigh molecular weight polyethylene (UHMWPE). The effects of UHMWPE on properties of composites were studied. The crystallinity of composites decreased slightly. Compared with non-UHMWPE added bamboo powder/HDPE composite, the composite with 6 wt % UHMWPE, showed decrease in water absorption to 0.41%, whereas its tensile strength and flexural strength increased to 34.51 and 25.88 MPa, respectively, a corresponding increase of 34.59 and 12.87%. The temperatures corresponding to initial degradation temperature (T_initial) and maximum degradation temperature (T_max) of the composite increased from 282.7 and 467.4 °C to 288.5 and 474.7 °C respectively. Scanning electron microscopic images showed that UHMWPE was well dispersed and fully extended as long fibers in the composite, forming a “three-dimensional physically cross-linked network structure,” which contributed to the improved properties of the composites. © 2020 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48971.     

Mechanical and tribological behaviors of polyamide 66/ultra high molecular weight polyethylene blends

The blends of polyamide (PA) and ultra high molecular weight polyethylene (UHMWPE) were prepared by a Brabender DSE25 co‐twin screw extruder, and maleic anhydride (MAH) grafted high‐density polyethylene (HDPE) was used as a compatibilizer. A chemical reaction between MAH group of MAH‐g‐HDPE and terminal amino group of PA was testified by FT‐IR analysis. Mechanical and tribological tests showed that the tensile and bending strength of PA decrease with the increase of UHMWPE. Besides, the mechanical strengths of PA/UHMWPE blends were improved by adding appropriate MAH‐g‐HDPE. The chemical reaction between MAH‐g‐HDPE and PA ameliorated the homogeneous dispersing ability of UHMWPE in the blend. The friction coefficient and volume wear rate of the PA/UHMWPE blends decreased apparently with the increase of UHMWPE, as was probably that UHMWPE has straight chain structure and good flexibility; therefore, a transferring film could be easily formed on the steel surface with the increase of UHMWPE. In friction process, the wear resistance of the blends was relative to the mechanical property of the blends when the amount of the transferring layer reached to a certain value. POLYM. ENG. SCI., 47:738–744, 2007. © 2007 Society of Plastics Engineers.     

Short‐time fabrication of well‐mixed high‐density polyethylene/ultrahigh‐molecular‐weight polyethylene blends under elongational flow: morphology,mechanical properties and mechanism

As linear polyethylenes, ultrahigh‐molecular‐weight polyethylene (UHMWPE) and high‐density polyethylene (HDPE) have the same molecular structure, but the large difference in viscosity between them makes it difficult to obtain well‐mixed blends. An innovative eccentric rotor extruder (ERE) generating an elongational flow was used to prepare HDPE/UHMWPE blends within short processing times. Compared with the obvious two‐phase morphology of a sample from a twin‐screw extruder observed with a scanning electron microscope, few small UHMWPE particles were observed in the HDPE matrix for a sample from the ERE, indicating the good mixing on a molecular level of HDPE/UHMWPE blends achieved by the ERE during short processing times. The morphological changes of blends prepared using the ERE evidenced the good integration of HDPE and UHMWPE even though the UHMWPE content is up to 50 wt% in the blends. Moreover, all blends retained most of the intrinsic molecular weight. The good mixing was further confirmed from the thermal, crystallization and rheological behaviors determined using differential scanning calorimetry and dynamic rheological measurements. Importantly, the 50/50 blend presented improved mechanical properties, especially super‐impact strength of 151.9 kJ m^?2 with incomplete‐break fracture state. The strengthening and great toughening effects of UHMWPE on the blends were attributed to the addition of unwrapped UHMWPE long molecular chains. The effective disentanglement mechanism of UHMWPE chains under elongational flow was explained schematically by a non‐parallel three‐plate model. © 2019 Society of Chemical Industry     

Influence of phase morphology on the sliding wear of polyethylene blends filled with carbon nanofibers

In this work, phase separation in carbon nanofiber (CNF) composites with a blend of ultrahigh molecular weight polyethylene (UHMWPE)/high‐density polyethylene (HDPE) was revealed, and its effects on tribological properties were investigated. Results from morphological analysis by optical and scanning electron microscopy indicated two distinct microstructures: a dispersed UHMWPE phase and a continuous microstructure containing HDPE and CNFs. The addition of CNFs into the UHMWPE/HDPE blend induced a decreased steady‐state torque indicative of a decreased dissolution and improved processability. Because CNFs predominantly resided into the HDPE phase, neat HDPE, a HDPE/CNF composite, and neat UHMWPE samples were also prepared for comparison. Wear results, determined by a pin‐on‐disk apparatus, showed that both initial run‐in and steady‐state wear rates of the UHMWPE/HDPE/CNF nanocomposites were reduced with an increasing concentration of CNFs. The wear resistance of the UHMWPE/HDPE blend was more strongly influenced than neat HDPE by the addition of CNFs, which may have been affected by a reduced dissolution and improved interfacial interaction between the two phases. Results from this study suggested that HDPE may not be appropriate for processing UHMWPE composites, as CNFs reside in the HDPE phase, and HDPE diminishes the wear resistance of the material. POLYM. ENG. SCI., 2010. © 2009 Society of Plastics Engineers     

Well-mixed blends of HDPE and ultrahigh molecular weight polyethylene with major improvements in impact strength achieved via solid-state shear pulverization

Compared with conventional polyolefins, ultrahigh molecular weight polyethylene (UHMWPE) possesses outstanding impact strength and crack resistance that make it desirable for a wide variety of applications. Unfortunately, UHMWPE has an ultrahigh viscosity that renders common, continuous melt-state processes ineffective for making UHMWPE products. Attempts to overcome this problem by blending UHMWPE with lower molecular weight high-density polyethylene (HDPE) by melt processing have typically led to poorly dispersed blends due to the vast viscosity mismatch between blend components. Here, we present solid-state shear pulverization (SSSP) as a mild, continuous, and simple approach for achieving effective and intimate mixing in UHMWPE/HDPE blends. These SSSP blends are easily processed by post-SSSP melt extrusion; for an SSSP blend with 50 wt% UHMWPE, we observe more than a factor of 1000 increase in viscosity at a shear rate of 0.01 s⁻¹ but less than a factor of 5 increase at 100 s⁻¹, the latter being more typical of melt-processing operations. Using extensional rheology, we confirm the strain hardening behavior of SSSP blends. Shear rheology and crystallization data show that the mixing between UHMWPE and HDPE can be improved with subsequent passes of SSSP and single-screw extrusion. Finally, we show that blending via SSSP leads to dramatic improvements in impact strength: as compared to literature results, injection-molded sample bars made from SSSP blends with 30–50 wt% UHMWPE exhibit very high values of notched Izod impact strength, 660–770 J/m (the impact strength of neat HDPE was 170 J/m).     

Isothermal crystallization kinetics and melting behavior of modified high‐density polyethylene/barium sulfate nanocomposites

The melting/crystallization behavior and isothermal crystallization kinetics of high‐density polyethylene (HDPE)/barium sulfate (BaSO₄) nanocomposites were studied with differential scanning calorimetry (DSC). The isothermal crystallization kinetics of the neat HDPE and nanocomposites was described with the Avrami equation. For neat HDPE and HDPE/BaSO₄ nanocomposites, the values of n ranges from 1.7 to 2.0. Values of the Avrami exponent indicated that crystallization nucleation of the nanocomposites is two‐dimensional diffusion‐controlled crystal growth. The multiple melting behaviors were found on DSC scan after isothermal crystallization process. The multiple endotherms could be attributed to melting of the recrystallized materials or the secondary lamellae caused during different crystallization processes. Adding the BaSO₄ nanoparticles increased the equilibrium melting temperature of HDPE in the nanocomposites. Surface free energy of HDPE chain folding for crystallization of HDPE/BaSO₄ nanocomposites was lower than that of neat HDPE, confirming the heterogeneous nucleation effect of BaSO₄. POLYM. COMPOS., 2011. © 2010 Society of Plastics Engineers     

Effective dissolution of UHMWPE in HDPE improved by high temperature melting and subsequent shear

A simple and effective way was expected to improve the blending of ultra‐high‐molecular‐weight polyethylene (UHMWPE) in high‐density polyethylene (HDPE) matrix. HDPE/UHMWPE blends were subjected to high temperature melting (HTM) at 280°C for up to 10 h, followed by shear at 175°C. These results were examined by scanning electron microscopy, polarized optical microscopy, and melt rheological behavior. UHMWPE particle was swelled partially during HTM, and this swollen region could be peeled from the particle by the subsequent shear, which resulted in more “dissolution” of UHMWPE in HDPE matrix. These results were also validated by the rheological behavior. POLYM. ENG. SCI., 55:270–276, 2015. © 2014 Society of Plastics Engineers     

Thermal properties,rheology and sintering of ultra high molecular weight polyethylene and its composites with polyethylene terephthalate

The addition of polyethylene terephthalate (PET) fibers in ultra high molecular weight polyethylene (UHMWPE) may be a promising approach to achieve improved wear properties in artificial joints. Since UHMWPE/PET composites are processed by compression molding, which involves compaction and sintering of polymeric powders, this article investigates their rheology, thermal properties, and sintering behavior to aid in the identification and selection of optimum processing conditions. Isothermal crystallization kinetics studies have revealed that crystallization of UHMWPE proceeds via heterogeneous nucleation and is governed by two‐dimensional growth. The crystallization rates of the composites were lower than those of the neat material, whereas their ultimate crystallinities were higher. The UHMWPE/PET composites had higher viscosity and elasticity than the neat resin. In the presence of PET fibers the onset of sintering took place at higher temperatures but proceeded at substantially higher rates as compared with pure UHMWPE. A marked discrepancy between the Eshelby‐Frenkel model and experimental sintering data suggests that viscous flow is not the prevailing mechanism for coalescence but rather that enhanced surface area, attributed to the highly developed internal morphology of UHMWPE particles, is the controlling factor. POLYM. ENG. SCI., 45:678–686, 2005. © 2005 Society of Plastics Engineers     

Viscosity and molecular weight distribution of ultrahigh molecular weight polyethylene using a high temperature low shear rate rotational viscometer

To obtain accurate measurements of the limiting viscosity number (LVN) or the intrinsic viscosity [η] of solutions of ultrahigh molecular weight polyethylene (UHMWPE), a low shear floating-rotor viscometer of the Zimm-Crothers type was constructed to measure viscosities at elevated temperatures (135°C) and near zero shear rate. The zero shear rate measurements for UHMWPE whole polymer and UHMWPE fractionated by hydrodynamic crystallization were compared with viscosity measurements at moderate and high shear rates (up to 2000 _s^?1) carried out in a capillary viscometer. The limiting viscosity number of UHMWPE decreases, as expected, with shear rate. The higher shear rate data could not be extrapolated to yield the correct zero-shear rate viscosities. Fractionation of UHMWPE gave 10 fractions ranging in LVN from 9 to 50 dL/g. A tentative integral molecular weight distribution for the whole polymer was calculated on the basis of the Mark-Houwink equation, but because it had been previously established only for lower molecular weight polyethylenes, it may not be accurate. A correlation was found between the LVNs for the fractions in the two types of viscometers.     

凝胶纺丝法制备超高分子量聚乙烯/高分子量聚乙烯纤维延伸性能的研究

用凝胶纺丝法制备了超高分子量聚乙烯(UHMWPE)/高分子量聚乙烯(HDPE)纤维,探讨了添加不同种类高分子量聚乙烯对凝胶初生纤维在后续延伸过程中延伸性能的影响。结果表明在固定制备条件时,当超高分子量聚乙烯(UHMWPE)/高分子量聚乙烯(HDPE)的质量比在最适当质量比时,高分子量聚乙烯的分子量为1.5～2.0×104时,所制备的凝胶初生纤维的可延伸比达最大值。     

Preparation of HDPE/UHMWPE/MMWPE blends by two-step processing way and properties of blown films

Summary Blends of high density polyethylene (HDPE) and ultra high molecular weight polyethylene (UHMWPE) were prepared by two-step processing way. Middle molecular weight polyethylene (MMWPE) as a fluidity modifier and compatilizer was added into UHMWPE in the first step, and then modified UHMWPE and HDPE were blending extruded to prepare the HDPE/UHMWPE/MMWPE blends used for blown films. The mechanical test of the blown films revealed that when the content of MMWPE in modified UHMWPE was 40wt% and the content of UHMWPE in the blends was 20 wt%, the film had the optimal mechanical properties. The tensile strength and tear strength of the film increased by 50% and 21%, respectively, compared with those of pure HDPE film. Rheological curves indicated that the melt torque and the apparent viscosity of the HDPE/UHMWPE/MMWPE blends made by two-step processing way both greatly reduced than other blends. The results from DSC suggested that the blends by two-step processing way may form more stable and perfect co-crystallization. PLM (polarized light microscopy) and SEM micrographs revealed that two-step processing way can improve the surface morphology of the films and make the dispersion of UHMWPE particles in HDPE increase.     

Preparation and characteristics of nano-B4C/PVA particles and ultra high molecular weight polyethylene composites

In-situ mechanical process for preparation of the polyvinyl alcohol (PVA) coated nano-B₄C powder was investigated by using a high-energy ball mill. The produced PVA coat on the surface of nano-B₄C particles was observed by x-ray diffraction (XRD) and confirmed by TEM images. The average particle size of the produced nano-B₄C/PVA particles was in the range of several tens to hundreds of nanometers depending on the milling conditions. The polymer composites were fabricated by hot pressing ultra high molecular weight polyethylene (UHMWPE) powder mixed with nano-B₄C/PAV and micro-B₄C powders, respectively. Nano-B₄C/PVA dispersed UHMWPE shows slightly lower crystallinity and stiffness than micro-B₄C dispersed UHMWPE based on differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA) evaluations.     

Bridged double percolation in conductive polymer composites: an electrical conductivity, morphology and mechanical property study

Conductive polymer composites are ubiquitous in technological applications and constitute an ongoing topic of tremendous commercial interest. Strategies developed to improve the level of electrical conductivity achieved at a given filler concentration have relied on double-percolated networks induced by immiscible polymer blends, as well as mixtures of fillers in a single polymer matrix, to enhance interparticle connectivity. In this work, we combine these two strategies by examining quaternary composites consisting of high-density polyethylene (HDPE), ultrahigh molecular weight polyethylene (UHMWPE), graphite (G) and carbon fiber (CF). On the basis of our previous findings, we examine the electrical conductivity, morphology, thermal signature and mechanical properties of HDPE/UHMWPE/G systems that show evidence of double percolation. Upon addition of CF, tremendous increases in conductivity are realized. The mechanism by which this increase occurs is termed bridged double percolation to reflect the role of CF in spanning non-conductive regions and enhancing the continuity of conductive pathways. At CF concentrations above the percolation threshold concentration, addition of G promotes increases in conductivity and dynamic storage modulus in which the conductivity increases exponentially with increasing modulus.     

Crystallization and stress relaxation behaviors of UHMWPE/CNT fibers

Crystallization and stress relaxation behaviors of ultrahigh molecular weight polyethylene (UHMWPE) doped with carbon nanotubes (CNTs) have been investigated by X‐ray diffraction, differential scanning calorimetry (DSC) and single strand strength testing. Compared with UHMWPE, crystallinity of the UHMWPE/CNT composites significantly increases from 71.95 to 82.92% while crystallization activation energy decreases from 679.4 to 535.8 KJ/mol. CNTs as the nucleating agent changes the nucleation type of UHMWPE from homogenous to heterogeneous and accelerates the nucleation and growing of crystalline grains. Above crystallization changes also affect the mechanical properties of the UHMWPE/CNTs composites. Stress relaxation testing indicates that the relaxation stability of UHMWPE/CNT composites increases while the relaxation rate decreases. J. VINYL ADDIT. TECHNOL., 24:229–232, 2018. © 2016 Society of Plastics Engineers     

Toughening high density polyethylene submitted to extreme ambient temperatures

The use of polyethylene is limited due to its low impact strength among other mechanical properties at extreme ambient temperatures, for example at ?46 °C and 66 °C. In this work, different polymer components, such as ultra-high molecular weight polyethylene (UHMWPE) and ethylene-vinyl acetate (EVA), were incorporated in high density polyethylene (HDPE) to test their ability to improve toughness of HDPE at extreme ambient temperatures. The polymer blends were processed by extrusion and injection molding and characterized by rotational rheometry, electron microscopy, thermal analysis, tensile, impact and dynamic mechanical tests. The results showed that low concentrations of EVA and UHMWPE in HDPE increased substantially the impact strength of HDPE at room temperature as well as in extreme ambient temperatures (?46 °C and 66 °C). This result indicates that these HDPE blends can be considered good candidates to replace pure HDPE in applications in which high values of toughness are required at extreme ambient temperatures.     

Crystallization and melting behavior of HDPE in HDPE/teak wood flour composites and their correlation with mechanical properties

The nonisothermal crystallization behavior and melting characteristics of high‐density polyethylene (HDPE) in HDPE/teak wood flour (TWF) composites have been studied by differential scanning calorimetry (DSC) and wide angle X‐ray diffraction (WAXD) methods. Composite formulations of HDPE/TWF were prepared by varying the volume fraction (?_f) of TWF (filler) from 0 to 0.32. Various crystallization parameters evaluated from the DSC exotherms were used to study the nonisothermal crystallization behavior. The melting temperature (T_m) and crystallization temperature (T_p) of the composites were slightly higher than those of the neat HDPE. The enthalpy of melting and crystallization (%) decrease with increase in the filler content. Because the nonpolar polymer HDPE and polar TWF are incompatible, to enhance the phase interaction maleic anhydride grafted HDPE (HDPE‐g‐MAH) was used as a coupling agent. A shift in the crystallization and melting peak temperatures toward the higher temperature side and broadening of the crystallization peak (increased crystallite size distribution) were observed whereas crystallinity of HDPE declines with increase in ?_f in both DSC and WAXD. Linear correlations were obtained between crystallization parameters and tensile and impact strength. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010