Sliding wear behaviour of oriented ultrahigh molecular weight polyethylene

The impact of processing‐induced chain orientation on the sliding wear behaviour of ultrahigh molecular weight polyethylene (UHMWPE) was investigated. The orientation of the molecular network of UHMWPE was done by means of uniaxial tension up to different residual strains. We found that high residual strain levels (higher than 0.45) enabled the sliding dissipated energy of UHMWPE to be decreased in dry conditions. In particular, oriented UHMWPE with a residual strain of 0.85 exhibited, at 500 000 sliding cycles in dry conditions, a decrease in volumetric wear loss by a factor of 3.3 and 19.4 compared with the reference UHMWPE tested in directions parallel and perpendicular to the chain direction, respectively. It is argued that oriented UHMWPE exhibits less adhesion during interfacial wear than the reference material, and hence orientation of UHMWPE bulk may be an alternative treatment to crosslinking for dry sliding conditions. In the case of sliding testing conducted in Ringer's solution, the benefit of the initial chain orientation was quite weak due to a lubrication effect of the solution that markedly limited the effect of chain orientation on the sliding behaviour.     

Tribological behavior of Ti3SiC2 and Ti3SiC2/Pb composites sliding against Ni-based alloys at elevated temperatures

The Ti₃SiC₂ and Ti₃SiC₂/Pb composites were tested under dry sliding conditions against Ni-based alloys (Inconel 718) at elevated temperatures up to 800 °C using a pin-on-disk tribometer. Detailed tribo-chemical changes of Pb on sliding surface were discussed. It was found that the tribological behavior were insensitive to the temperature from 25 °C (RT) to 600 °C (friction coefficient ≈0.61–0.72, wear rate ≈10⁻³ mm³ N m⁻¹). An amount of Pb in the composites played a key role in lubricating with the temperature below 800 °C. The friction coefficient (≈0.22) and wear rate (≈10⁻⁷ mm³ N m⁻¹) at elevated temperatures were both decreased by the added PbO. The wear mechanisms of Ti₃SiC₂/Pb-Inconel 718 tribo-pair at elevated temperatures were believed to be the combined effect of abrasive wear and tribo-oxidation wear. During the sliding, two oxidization reactions proceed, 2Pb+O₂=2PbO (below 600 °C) and 6PbO+O₂=2Pb₃O₄ (800 °C). The friction coefficient and wear rate of the composites were reduced due to the self-lubricating effect of the tribo-oxidation products.     

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.     

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。     

Effects of (Ta0.2W0.2Nb0.2Mo0.2V0.2)C high-entropy carbide content on the microstructure and properties of Ti(C0.7N0.3)-based cermet

Using pre-synthesized high-entropy (Ta_0.2W_0.2Nb_0.2Mo_0.2V_0.2)C carbide as the reinforcing phase, Ti(C_0.7N_0.3)-based cermets were prepared by pressureless sintering at 1600 °C. The results revealed that due to the solid solution reaction between the mono-carbide and (Ta_0.2W_0.2Nb_0.2Mo_0.2V_0.2)C, only one set of face-centered-cubic diffraction peaks in XRD was detected in the as-sintered cermets, alongside the typical core-rim structure. Compared to the Ti(C_0.7N_0.3)-based cermets without high-entropy reinforcing phase, the Vickers hardness was increased from 17.06 ± 0.09 GPa to 18.42 ± 0.33 GPa and the fracture toughness was increased from 9.21 ± 0.31 MPa m^1/2 to 12.56 ± 0.23 MPa m^1/2 by adding 10 wt% (Ta_0.2W_0.2Nb_0.2Mo_0.2V_0.2)C. The wear resistance of the cermet was enhanced significantly with increasing (Ta_0.2W_0.2Nb_0.2Mo_0.2V_0.2)C content. This work provided a potential that the high-entropy carbide can be applied as an effective reinforcing phase in the preparation of high-performance Ti(C_0.7N_0.3)-based cermets.     

Mechanical properties study of micro‐ and nano‐hydroxyapatite reinforced ultrahigh molecular weight polyethylene composites

This is a comparative study between ultrahigh molecular weight polyethylene (UHMWPE) reinforced with micro‐ and nano‐hydroxyapatite (HA) under different filler content. The micro‐ and nano‐HA/UHMWPE composites were prepared by hot‐pressing method, and then compression strength, ball indentation hardness, creep resistance, friction, and wear properties were investigated. To explore mechanisms of these properties, differential scanning calorimetry, infrared spectrum, wettability, and scanning electron microscopy with energy dispersive spectrometry analysis were carried out on the samples. The results demonstrated that UHMWPE reinforced with micro‐ and nano‐HA would improve the ball indentation hardness, compression strength, creep resistance, wettability, and wear behavior. The mechanical properties for both micro‐ and nano‐HA/UHMWPE composites were comparable with pure UHMWPE. The mechanical properties of nano‐HA/UHMWPE composites are better compared with micro‐HA/UHMWPE composites and pure UHMWPE. The optimum filler quantity of micro‐ and nano‐HA/UHMWPE composites is found to be at 15 wt % and 10 wt %, separately. The micro‐ and nano‐HA/UHMWPE composites exhibit a low friction coefficient and good wear resistance at this content. The worn surface of HA/UHMWPE composites shows the wear mechanisms changed from furrow and scratch to surface rupture and delamination when the weight percent of micro‐ and nano‐HA exceed 15 wt % and 10 wt %. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 42869.     

Mechanism of size effects of a filler on the wear behavior of ultrahigh molecular weight polyethylene

Although the size effects of a filler are closely related to the complex multi-level structures of their polymer composites; unfortunately, such relationships remain poorly understood. In this study, we investigated the effects of various sizes (40-600 nm) of silicon carbide (SiC) fillers on the wear behavior of ultrahigh molecular weight polyethylene (UHMWPE) in the presence of the silane coupling agent KH-560. All of these SiC fillers improved the wear resistance of UHMWPE significantly, with a medium size (150 nm) being optimal. To examine the reasons for this behavior, we analyzed the multi-level structures of the samples in terms of their matrix structures (crystalline; amorphous; interphase), matrix-filler interactions (physical adsorption; chemical crosslinking; hybrid network) and the external effects of SiC fillers (bearing loads; transferring frictional heat). The high rigidity and thermal conductivity of SiC fillers and, more importantly, the intrinsic characteristics of the matrix structures (larger crystal grains; higher interphase; stronger amorphous entangled networks) were the key parameters affecting the enhancement in the wear-resistance of the UHMWPE. Herein, we also provide interpretations of the corresponding physical effects. Our results should improve our understanding of the structure-property relationships and, thus, should guide the formula design of UHMWPE composites.     

Effects of a coupling agent on the mechanical and thermal properties of ultrahigh molecular weight polyethylene/nano silicon carbide composites

Ultra‐high‐molecular‐weight polyethylene (UHMWPE)/nano silicon carbide (nano‐SiC) composites were prepared by compression molding. The effects of a coupling agent and the content of the filler on the filler dispersion and the mechanical and thermal properties of the composites were investigated. The results show that the mechanical properties of the composites first increased and then decreased with increasing SiC content. The macromolecular coupling agent exhibited a much better reinforcing effect than the small‐molecule coupling agent. The tensile strength of the composites with 3‐aminopropyltriethoxysilane (KH550), γ‐methacryloxypropyltrimethoxysilane (KH570), and silicone powders reached its maximum value when the silicon carbide (SiC) content was 3%. We found that a web of the UHMWPE/SiC/coupling agent was formed and played a significant role in improving the heat resistance of the composites. In addition, appropriate amounts of SiC could increase the crystallinity of UHMWPE via a process of heterogeneous nucleation. The comprehensive performance of the KH550/silicone/SiC/UHMWPE composites was the best. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Effects of carbon black on tribology of blends of poly(vinylidene fluoride) with irradiated and non-irradiated ultrahigh molecular weight polyethylene

Friction and wear resistance are two vital tribological properties of polymer-based materials but optimization of both is rarely attempted. We have investigated blends of 70 wt% poly(vinylidene fluoride) (PVDF)+30% ultra high molecular weight polyethylene, the latter either un-irradiated or else γ-irradiated. Each sample contained varying amounts of carbon black (CB) and also had a varied degree of crosslinking and irradiation dose. We have determined static and dynamic friction, scratch resistance, and sliding wear in multiple scratching tests. Effects of the irradiation dose and CB concentration have been quantified. The electric conductivity threshold is reflected in a drop of static friction; formation of a continuous phase of the lubricant affects tribology as well as electrical properties—both for irradiated and for un-irradiated samples. The scratch resistance as represented by the residual (healing) depth is affected by crosslinking, by the stage at which irradiation is applied (before or after blending) and by CB addition. Crosslinking by moderate amounts of irradiation provides shallower residual depths while higher doses cause adverse results. Similarly, the CB lubricant can either improve or worsen the scratch resistance. A combination of both approaches produces either better or else worse results than crosslinking alone. Lower friction seems accompanied by higher scratch resistance. A combination of a specific irradiation dose and an optimized CB concentration lowers the sliding wear significantly. Strain hardening in sliding wear determination takes place for all materials studied, irrespective of the extent or radiation-induced crosslinking and of the presence and concentration of carbon black.     

Positive temperature coefficient and time‐dependent resistivity of carbon nanotubes (CNTs)/ultrahigh molecular weight polyethylene (UHMWPE) composite

The carbon nanotubes/ultrahigh molecular weight polyethlene (CNTs/UHMWPE) conductive composite with a low percolation threshold had been successfully fabricated, and CNTs were only dispersed in the interface of matrix particles. Some factors, including CNTs concentration, processing temperature, and the time of isothermal treatment, which could exert influence on the positive temperature coefficient effect of the composite, were investigated. Similar with negative temperature coefficient effect, the resistivity decreased during isothermal treatment above the melting point of UHMWPE, which could be thought to be a relaxation process originated from movement of molecular chains. This relaxation, also a process of CNTs aggregating to reorganize the conductive network, was testified as a function of time, temperature, filler concentration, and heating rate. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Tribological investigations of carbon nanotube‐reinforced polymer (UHMWPE) nanocomposites using Taguchi methodology

Taguchi design techniques have been applied to investigate the significant influence of various operating and design parameters, such as contact load, rotational sliding speed, and carbon nanotubes (CNTs) concentration on the tribological properties of ultra‐high molecular weight polyethylene nanocomposites. Analysis of variance was conducted to discuss the significance of each of the parameters. Simple regression models were developed for wear rate as well as for the coefficient of friction (COF) of the nanocomposite. Applied normal force was found to be the dominant factor controlling the wear rate and friction coefficient. The significance of CNTs concentration on both COF and wear rate closely follow that of applied load. Rotational sliding speed has the least influence on the tribological properties of the nanocomposite. The developed model for predicting wear rate and the COF was found to give very good predictions against the experimental data. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44018.     

Toughness enhancement of poly(ethylene terephthalate) with functionalized ultrahigh molecular weight polyethylene

Ultrahigh molecular weight polyethylene (UHMWPE) is available commercially in the form of powder, consisting of fine primary particles, 1–5 μm in diameter, agglomerated into secondary “free‐flowing” particles with overall dimensions in the region of 50 to 150 μm. These are normally sufficiently coherent and retain their conglomerated particulate structure when blended with other polymers because of the extremely high viscosity of UHMWPE. In this study the surface of the agglomerated primary particles was acid functionalized by reactions with aqueous solutions of acrylic acid, after being irradiated with γ‐radiation at 15–45 kGy. The acid groups were used to introduce a glycidoxyl functionality through reactions with a difunctional cycloaliphatic epoxy resin and also to a “partial” metal carboxylate functionality through reactions with zinc acetyl acetonate. When blended with polyethylene terephthalate (PET) in either a small‐batch mixer or in a twin‐screw extruder all the treated powders, except those functionalized with acrylic acid, were broken down to their primary size and were uniformly dispersed and strongly bonded to the surrounding matrix. The blends containing the deglomerated particles were found to have much greater ductility and toughness than those produced from both untreated and acid functionalized powder. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 2972–2986, 2001     

Effects of acid oxidation on wetting and adhesion properties of ultra-high modulus and molecular weight polyethylene (UHMWPE) fibers

The effects of acid oxidation on the surface properties of gel-spun ultra-high modulus and molecular weight polyethylene (UHMWPE) fibers were investigated. Three acid-assisted reactions with CrO₃ (I), K₂Cr₂O, (II), and one base-catalyzed reaction with K₂Cr₂O₇ (III) were studied. In reaction II, two levels of sulfuric acid were used for IIa and IIb, with reaction IIa containing the higher concentration. Under the reaction conditions chosen, i.e. 1 min at 23°C, the effects of these oxidations were restricted to the fiber surfaces. All oxidation reactions either significantly reduced or eliminated the axially oriented macrofibril striations and changed the lamellae perpendicular to the fiber axis to irregular hairline surface structures. The oxidative attacks on the fiber surfaces appeared to have occurred in the fibrillar structure and likely at the disorder regions along the fibrils. The epoxy resin wettability and the interfacial adhesion to the epoxy resin were both improved with reactions I and IIa, whereas reaction III did not affect either of these properties. A positive relationship between surface wettability and interfacial adhesion on single fibers was observed on the untreated and acid oxidized gel-spun UHMWPE fibers.     

Preparation and cutting performance of Ti(C7, N3)/TiB2/WC cermet tool material

In this paper, a Ti(C₇, N₃)/TiB₂/WC cermet tool material was prepared by plasma sintering. The components of the tool material and sintering process parameters were optimized through testing mechanical property. The cutting performance of the prepared tool was studied in the cutting experiment of 06Cr19Ni10 austenitic stainless steel. A comparison was made between the prepared tool and the commercial cermet tool SNMN120708. It is shown that when the volume fractions of TiB₂ and WC were 20% and 15%, respectively, at the sintering temperature of 1550 °C and with the holding time of 30 min, the prepared tool would possess the flexural strength of 1096.45 Mpa, the hardness of 18.9 Gpa, the fracture toughness of 9.85 Mpa·m^1/2 and the optimal cutting speed of 150 m/min. At the cutting speeds of 100 m/min and 150 m/min, the cutting distance of the developed tool was larger than that of SNMN120708. When the cutting speeds were 200 m/min and 250 m/min, the cutting distance of SNMN120708 tool was relatively large. The main wear mechanism of Ti(C₇, N₃)/TiB₂/WC and SNMN120708 tool was adhesive wear, with no trace of abrasive wear.     

Toughening of dimethacrylate resins by addition of ultra high molecular weight polyethylene (UHMWPE) particles

The effects of the addition of UHMWPE particles, of nominal 〈80 μm〉 size, on the fracture toughness, flexural modulus and strength of composites made with dimethacrylate resins (60/40 wt/wt BisGMA-TEGMA) were investigated as a function of volume fraction of UHMWPE (0-60 vol%) and particle surface treatment. Interfacial shear strengths (τ) were measured via microbond shear strength tests using Spectra900™ (UHMWPE) fibers and BisGMA-TEGMA beads. τ increased by a factor of 4 compared with untreated UHMWPE, and surface treated particles improved the mechanical properties of the composite. Fracture toughness (K_IC) and flexural modulus (E) increased with increased volume fraction of UHMWPE, with maximum K_IC/E increases (at 60 vol%) of 238%/25% compared with the neat resin. SEM images showed debonding as well as yielding and fibrillation of the UHMWPE particles, suggesting that these were significant toughening mechanisms.     

Morphology and mechanical properties of injection‐molded ultrahigh molecular weight polyethylene/polypropylene blends and comparison with compression molding

The mechanical properties and morphology of UHMWPE/PP(80/20) blend molded by injection and compression‐molding were investigated comparatively. The results showed that the injection‐molded part had obviously higher Young's modulus and yield strength, and much lower elongation at break and impact strength, than compression‐molded one. A skin‐core structure was formed during injection molding in which UHMWPE particles elongated highly in the skin and the orientation was much weakened in the core. In the compression‐molded part, the phase morphology was isotropic from the skin to the core section. The difference in consolidation degree between two molded parts that the compression molded part consolidated better than the injection one was also clearly shown. In addition, compositional analysis revealed that there was more PP in the skin than core for the injection‐molded part, whereas opposite case occurred to the compression‐molded one. All these factors together accounted for the different behavior in mechanical properties for two molded parts. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Comparison of sintering behavior and reinforcing mechanisms between 3Y-TZP/Al2O3(w) and 12Ce-TZP/Al2O3(w) composites: Combined effects of lanthanide stabilizer and Al2O3 whisker length

The densification behavior, microstructural development, toughening and strengthening mechanisms of Al₂O₃ whisker-reinforced 3Y-TZP and 12Ce-TZP composites were systematically and comparatively investigated with varying whisker lengths. Compared with 3Y-TZP/A_w composites, the presence of a Ce-Al-Si-O amorphous phase, caused by the addition of Al₂O₃ whiskers, promoted the densification and grain growth of 12Ce-TZP/A_w composites. Crack deflection and bridging are proposed as the primary toughening mechanisms for 3Y-TZP/A_w composites, while the t-m martensitic transformation would dominate the toughening and strengthening processes of 12Ce-TZP/A_w composites. Changes in Al₂O₃ whisker length would vary the distributions of internal stress and amorphous phase within the ceria-stabilized ZrO₂ matrix, and hence affect the toughening and strengthening results. It indicates that effective toughening and strengthening of the Al₂O₃ whisker-reinforced TZP composites can be achieved by taking advantage of collaborative engineering control on the reinforcement morphology and the interface chemistry/structure.     

Dissipative particle dynamics study on the phase morphologies of the ultrahigh molecular weight polyethylene/polypropylene/poly(ethylene glycol) blends

The dissipative particle dynamics (DPD) simulation method has been used to study mesophase formation of the binary UHMWPE/PP and ternary UHMWPE/PP/PEG blends. The effects of shear rates and volume fractions of each of the blend components on end-to-end distances of UHMWPE, diffusivities and mesoscale morphologies of the blends have been investigated in detail. As compositions of the UHMWPE/PP and UHMWPE/PP/PEG blends vary, the mesoscale simulations have predicted the ordered structures with defined morphologies of lamellas, perforated lamellas, hexagonal spheres, and body-centered-cubic spheres. Micelle-like melted structures between totally disordered and the ordered phases have also been found in the UHMWPE/PP (10/90) blends. Immiscibility property of UHMWPE, PP and PEG induces the phase separation and exhibits different mesoscpic morphologies at different shear rates and volume fractions. Taking the shear rates dependence of mesophase into account, the change in morphology of the UHMWPE/PP/PEG blends with shear rate is also well studied in this work. As a function of PP concentration, the end-to-end distances of UHMWPE are found to decrease with the increase of PP concentration. This effect is more prominent for a high amount of PP.     

高耐磨耐腐蚀改性超高分子量聚乙烯特种管材的研制

深入研究采用一种分子量在100～500万的新型塑料管道加工材料--超高分子量聚乙烯树脂(UHMWPE)为主要原材料添加一定比例的内润滑剂、外润滑剂、成核剂、流动性加工助剂等辅助材料,通过各种原辅材料共混改性后,运用近熔点挤出原理和特殊工艺控制,通过管材挤出生产线挤出成型为高耐磨耐腐蚀的特种塑料管材,使得该管材有着众多的聚合物材料所无法比拟的优异的物理何化学性能。