Ultra-high Molecular Weight Polyethylene Matrix Research Articles

Polymer Composites with Carbon Fillers Based on Coal Pitch and Petroleum Pitch Cokes: Structure, Electrical, Thermal, and Mechanical Properties.

The effect of particle size and oxidation degree of new carbon microfillers, based on coal pitch (CP) and petroleum pitch (PET) cokes, on the structure as well as thermal, mechanical, and electrical properties of the composites based on ultrahigh molecular weight polyethylene (UHMWPE) was investigated. The composites studied have a segregated structure of filler particle distribution in the UHMWPE matrix. It was found that composite with smaller CP grain fraction has the highest Young's modulus and electrical conductivity compared to the other composites studied, which can be the result of a large contribution of flake-shaped particles. Additionally, conductivity of this composite turned out to be similar to composites with well-known carbon nanofillers, such as graphene, carbon black, and CNTs. Additionally, the relationship between electrical conductivity and Young's modulus values of composites studied was revealed, which indicates that electrical conductivity is very sensitive to the structure of the filler phase in the polymer matrix. In general, it was established that the properties, especially the electrical conductivity, of the composites studied strongly depends on the size, shape, and oxidative treatment of CP and PET filler particles, and that the CP coke of appropriately small particle sizes and flake shape has significant potential as a conductive filler for polymer composites.

Investigating the effect of simultaneous incorporation of Al2O3 and B4C nanofillers in enhancing the wear performance of UHMWPE

AbstractDuring the past years, great effort has been made to improve the tribological performance of ultra‐high molecular weight polyethylene (UHMWPE), considered a key polymeric material in applications requiring elevated mechanical and corrosion resistance and bioinertness. This work aimed to investigate the role of adding ceramic nanofillers of aluminum oxide (Al2O3) and boron carbide (B4C) in the UHMWPE matrix in order to modify the triboperformance of the polymer. The results obtained through dry reciprocating sliding tests up to 6 h (21,600 cycles) revealed that the presence of nanoparticles has led to a 33% higher coefficient of friction on average when compared with the matrix polymer without nanofillers. This behavior results from the increased resistance to plowing caused by the nanofillers, which contributes to the frictional force. Conversely, the simultaneous utilization of both nanofillers, each one at a concentration of 1.5% by mass, significantly enhances the wear resistance of UHMWPE, achieving a reduction in wear of over 35%.

Efficient construction of graphite long-range ordered structure in ultra-high molecular weight polyethylene matrix via continuous solid-state extrusion

In the present work, with a unique eccentric rotor solid extruder, ultra-high molecular weight polyethylene/natural graphite (UHMWPE/NG) oriented composites were fabricated by establishing a three-dimensional (3D) oriented segregated thermal conductive network at 120 °C, the temperature of the softening state of UHMWPE matrix. The as-prepared composites exhibited high thermal conductivity (6.76 W⋅m−1K−1) and low surface resistivity (0.152 Ω cm) at 29.4 vol% NG loading, making them possess the tremendous development potential and prospects for electronic packaging applications. The research provided an efficient and green as well as low-cost method for manufacturing high-performance thermal interface materials (TIMs).

Superhydrophobic ultra-high molecular weight polyethylene nanocomposite foams fabricated by supercritical CO2 foaming for selective oil absorption

Superhydrophobic foams are promising substances for removing leaked oil from water. However, producing superhydrophobic foams with stable high performance using a low-cost, scalable, and environmentally friendly means is a challenge. Herein, superhydrophobic nanocomposite foams comprising of ultra-high molecular weight polyethylene (UHMWPE) and modified silica nanoparticles (NPs) were developed using melt blending and supercritical CO2 foaming. Long carbon chains grafted on silica NPs formed a shell with a thickness of 100 nm, which rendered the NPs hydrophobicity and generated entanglements with UHMWPE matrix. The optimum foam with an average cell size of 41.5 μm achieved a high water contact angle of 158.2 ± 1° and a low sliding angle of 1.7 ± 0.4°, attributing to the micro-nano hierarchical structure constructed by the porous structure and the modified NPs. The foam remained superoleophilic and demonstrated high efficiency in separating both light and heavy oils from water. A relatively high oil absorption capacity of 2.8 to 7.2 g/g was achieved towards various oils and solvents, and separation efficiency of over 99 % could be maintained after ten cycles of reuse. This work provides a facile and scalable method to produce superhydrophobic UHMWPE nanocomposite foams with stable high performance for effective oil absorption from water.

Simulation of Neutron/Self-Emitted Gamma Attenuation and Effects of Silane Surface Treatment on Mechanical and Wear Resistance Properties of Sm2O3/UHMWPE Composites.

This work reports on the simulated neutron and self-emitted gamma attenuation of ultra-high-molecular-weight polyethylene (UHMWPE) composites containing varying Sm2O3 contents in the range 0–50 wt.%, using a simulation code, namely MCNP-PHITS. The neutron energy investigated was 0.025 eV (thermal neutrons), and the gamma energies were 0.334, 0.712, and 0.737 MeV. The results indicated that the abilities to attenuate thermal neutrons and gamma rays were noticeably enhanced with the addition of Sm2O3, as seen by the increases in µm and µ, and the decrease in HVL. By comparing the simulated neutron-shielding results from this work with those from a commercial 5%-borated PE, the recommended Sm2O3 content that attenuated thermal neutrons with equal efficiency to the commercial product was 11–13 wt.%. Furthermore, to practically improve surface compatibility between Sm2O3 and the UHMWPE matrix and, subsequently, the overall wear/mechanical properties of the composites, a silane coupling agent (KBE903) was used to treat the surfaces of Sm2O3 particles prior to the preparation of the Sm2O3/UHMWPE composites. The experimental results showed that the treatment of Sm2O3 particles with 5–10 pph KBE903 led to greater enhancements in the wear resistance and mechanical properties of the 25 wt.% Sm2O3/UHMWPE composites, evidenced by lower specific wear rates and lower coefficients of friction, as well as higher tensile strength, elongation at break, and surface hardness, compared to those without surface treatment and those treated with 20 pph KBE903. In conclusion, the overall results suggested that the addition of Sm2O3 in the UHMWPE composites enhanced abilities to attenuate not only thermal neutrons but also gamma rays emitted after the neutron absorption by Sm, while the silane surface treatment of Sm2O3, using KBE903, considerably improved the processability, wear resistance, and strength of the composites.

Spectroscopic Study of Ultra High Molecular Weight Polyethylene (UHMWPE) and Mg-Ni-doped ZnFe<SUB>2</SUB>O<SUB>3</SUB> Nano Composites

The present study aims at investigating the effect of incorporating nano scale MgxNixZn1-xFe2O3 (where x=0.15) as nano fillers on the physical and chemical stability of ultra high molecular weight polyethylene (UHMWPE). The effect of adding 1% and 2% (by weight) nano fillers on the physicochemical properties of UHMWPE/MgxNixZn1-xFe2O3 nano composites have also been investigated by using FTIR, Raman, and UV-VIS spectroscopy. FTIR data of UHMWPE/MgxNixZn1-xFe2O3 nano composites reveal that the addition of MgxNixZn1-xFe2O3 up to 1% induces significant chemical and physical structural alterations in UHMWPE matrix. However, this behavior is found to reduce on increasing the concentration of nano fillers from 1% to 2%. Raman spectroscopic data shows that crystalline contents of UHMWPE remain unaffected with the addition of nano fillers, however; a significant increase in amorphous contents and decrease in all-trans interphase region is observed. This behavior is attributed to the chain scission reactions due to addition of MgxNixZn1-xFe2O3 followed by compression moulding process at high pressure and elevated temperature. Absorption spectroscopy analysis revealed that the incorporation of MgxNixZn1-xFe2O3 results in decrease of energy band gaps from 2.14 eV to 2.08 eV (for direct transition) and from 1.54 eV to 1.38eV (for indirect transition) due to band gap energy which is induced because of MgxNixZn1-xFe2O3 incorporation as nano fillers within the PE matrix.

Effects of attapulgite on the worn surface and fretting wear resistance property of UHMWPE composites

PurposeThe purpose of this study is to examine the fretting wear property of ultra-high molecular weight polyethylene (UHMWPE)-based composites reinforced by different content of attapulgite.Design/methodology/approachA series of composites were prepared by a hot-pressing method. Fretting tests were carried out using an SRV-IV oscillating reciprocating friction wear tester with a load of 10 N and a frequency of 100 Hz. The morphology of the fracture structure and the worn surface was observed by field-emission scanning electron microscopy, X-ray diffraction and a non-contact three dimensional surface profiler.FindingsWith the addition of attapulgite, the microstructure of the composites become more regular, and their heat resistance improved. Furthermore, the friction coefficient and the specific wear rate of the composites with lower filler content reduced compared with that of neat UHMWPE, and the optimum filler content is 1 per cent.Originality/valueThe study investigated the fretting resistance mechanism of the attapulgite in the UHMWPE matrix. The results could help to provide some experimental evidence for the broader application of silicates on the fretting wear resistance of polymers.Peer reviewThe peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-10-2019-0420/

Enhanced fretting wear performance of UHMWPE composites by grafting Co–Ni layered double hydroxides on attapulgite nanofibers

In this study, attapulgite (ATP) nanofibers were modified by hydrotalcite-like cobalt-nickel via hydrothermal (named ATP-CoNi(H)) and co-precipitation (named ATP-CoNi(C)) method, respectively. The morphology and the composition of the ATP-CoNi hybrids were investigated. Meanwhile, the fretting wear properties of ultra-high molecular weight polyethylene (UHMWPE)-based composites reinforced by ATP and two kinds of ATP-CoNi hybrids at 2 wt% content were investigated. The results show that ATP-CoNi hybrids exhibit better fretting wear properties than pure ATP in the UHMWPE matrix. Thereinto, the ATP-CoNi(C) nanofibers present the best antifriction property that the friction coefficient and wear volume severally decreased by 27% and 47%. It is attributed to the optimal interfacial bonding between the nanofibers and the matrix, which makes the dense structure of the composite.

The influence of several silicates on the fretting behavior of UHMWPE composites

AbstractFive kinds of silicates (attapulgite, kaolin, montnorillonite, synthetic mica, and talc) reinforced ultra‐high molecular weight polyethylene (UHMWPE) composites were prepared. The fretting performance of the composites was investigated using an oscillating reciprocating friction and wear tester in a ball‐on‐plate mode. The thermodynamic property and crystallinity of the composites were evaluated, and the worn morphology was also observed. Result shows that the heat‐resistance and the crystallinity of the composites are generally improved. The friction coefficient and mass loss of the composites reduced than those of the neat UHMWPE. Thereinto, the attapulgite/UHMWPE composite shows the best fretting resistance performance. The heat resistance of composites increases due to the reinforcement of silicates. Meantime, the friction load can be distributed by the filler in the matrix. Moreover, the different fretting resistance performance of the composites is due to the different dispersion degree and the interfacial bonding force between the fillers and the UHMWPE matrix.

Influence of ultrasonic treatment on mechanical and electro-physical characteristics of UHMWPE/MWCNT composites

The influence of ultrasonic treatment on the strength and dielectric properties of composites based on ultra-high molecular weight polyethylene (UHMWPE) and multi-walled carbon nanotubes (MWCNT) is studied. It is revealed that the ultrasonic treatment of composite melt at 130 °C results in the uniform distribution of nanotubes in the UHMWPE matrix, an increase in the degree of composite crystallinity by 10%, an increase in abrasion resistance by 37%, an increase in elongation at rupture by a factor of 2. The change in the physical and mechanical properties of the composite is caused by the change in the polymer matrix structure, taking place as a result of ultrasonic action, and does not depend on the presence of nanotubes in the polymer matrix.

SiO2‐covered graphene oxide nanohybrids for in situ preparation of UHMWPE/GO(SiO2) nanocomposites with superior mechanical and tribological properties

ABSTRACTThe modified Hummer technique was used in the preparation of graphene oxide (GO) nanosheets, and then SiO2 decorated GO [GO(SiO2)] nanosheets were synthesized via the sol–gel method. Then, ultrahigh‐molecular‐weight polyethylene (UHMWPE) nanocomposites loaded with 0.5, 1, 1.5, and 2 wt % of GO(SiO2) were prepared using magnesium ethoxide/GO(SiO2)‐supported Ziegler–Natta catalysts via the in situ polymerization. Morphological study of the prepared polymer powders was assessed using field‐emission scanning electron microscopy, which showed that GO(SiO2) nanohybrids have been uniformly dispersed and distributed into the UHMWPE matrix. Also, the neat UHMWPE and its nanocomposites were evaluated with different analyses, including viscosity‐average molecular weight measurement, differential scanning calorimetry, thermogravimetric analysis, tensile test, scratch hardness, and pin‐on‐disk test. The characterization of the UHMWPE nanocomposites indicated that many characterizations, including the mechanical, thermal, and tribological properties of UHMWPE, were significantly improved by incorporation of these new nanosheets in spite of the molecular weight reduction of the polymeric matrix and the improved flowability and processability of the produced nanocomposite. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47796.

UHMWPE/organoclay nanocomposites fabricated by melt intercalation under continuous elongational flow: Dispersion, thermal behaviors and mechanical properties

The preparation of ultra‐high‐molecular weight polyethylene (UHMWPE)/organoclay nanocomposites by continuous elongational flow technique was investigated in a novel eccentric rotor extruder (ERE). The distribution and dispersion morphologies of organo‐modified montmorillonite (OMMT) layers were revealed and observed by ash determination, wide angle X‐ray diffraction and transmission electron microscopy. The thermal and thermal‐mechanical behaviors were characterized by differential scanning calorimeter, thermal gravimetric analysis and dynamic mechanical thermal analysis. The mechanical performances was measured by tensile and impact test. The morphologies of the nanocomposites evidenced that the OMMT layers can be well intercalated or/and exfoliated by UHMWPE matrix, then the fabrication mechanism of intercalated and exfoliated OMMT structures under continuous elongational flow was discussed. The ideal dispersion of OMMT in UHMWPE matrix obviously improved the crystallinity and the mechanical properties at a certain concentration of OMMT loading, indicating that the lower OMMT addition can lead an effective strengthening and toughening for UHMWPE. POLYM. ENG. SCI., 59:547–554, 2019. © 2018 Society of Plastics Engineers

Simultaneously enhanced mechanical properties and thermal properties of ultrahigh‐molecular‐weight polyethylene with polydopamine‐coated α‐alumina platelets

AbstractPolydopamine (PDA) was employed to modify micrometric Al2O3 platelets to improve the interfacial compatibility between α‐Al2O3 powder and ultrahigh‐molecular‐weight polyethylene (UHMWPE). The structure of PDA‐coated Al2O3 and UHMWPE composites was investigated via Fourier transform infrared spectroscopy, scanning electron microscopy and X‐ray photoelectron spectroscopy. The thermal stability and mechanical performance of the samples were also evaluated. It is clear that UHMWPE/PDA‐Al2O3 composites exhibit better mechanical properties, higher thermal stability and higher thermal conductivity than UHMWPE/Al2O3 composites, owing to the good dispersion of Al2O3 powder in the UHMWPE matrix and the strong interfacial force between the macromolecules and the inorganic filler caused by the presence of PDA. The tensile strength and the tensile elongation at break of UHMWPE/PDA‐Al2O3 composite with 1 wt% PDA‐Al2O3 are 62.508 MPa and 462%, which are 1.96 and 1.98 times higher than those of pure UHMWPE, respectively. The thermal conductivity of UHMWPE/PDA‐Al2O3 composite increases from 0.38 to 0.52 W m−1 K−1 with an increase in the dosage of PDA‐Al2O3 to 20 wt%. The results show that the prepared PDA‐coated Al2O3 powder can simultaneously enhance the mechanical properties and thermal conductivity of UHMWPE. © 2018 Society of Chemical Industry

Self-sensing and mechanical performance of CNT/GNP/UHMWPE biocompatible nanocomposites

Ultra-high molecular weight polyethylene (UHMWPE)-based conductive nanocomposites with reduced percolation and tunable piezoresistive behavior were prepared via solution mixing followed by compression molding using carbon nanotubes (CNT) and graphene nanoplatelets (GNP). The effect of varying wt% of GNP with fixed CNT content (0.1 wt%) on the mechanical, electrical, thermal and piezoresistive properties of UHMWPE nanocomposites was evaluated. The combination of CNT and GNP enhanced the dispersion in UHMWPE matrix and lowered the probability of CNT aggregation as GNP acted as a spacer to separate the entanglement of CNT with each other. This has allowed the formation of an effective conductive path between GNP and CNT in UHMWPE matrix. The thermal conductivity, degree of crystallinity and degradation temperature of the nanocomposites increased with increasing GNP content. The elastic modulus and yield strength of the nanocomposites were improved by 37% and 33%, respectively, for 0.1/0.3 wt% of CNT/GNP compared to neat UHMWPE. The electrical conductivity was measured using four-probe method, and the lowest electrical percolation threshold was achieved at 0.1/0.1 wt% of CNT/GNP forming a nearly two-dimensional conductive network (critical value, t = 1.20). Such improvements in mechanical and electrical properties are attributed to the synergistic effect of the two-dimensional GNP and one-dimensional CNT which limits aggregation of CNTs enabling a more efficient conductive network at low wt% of fillers. These hybrid nanocomposites exhibited strong piezoresistive response with sensitivity factor of 6.2, 15.93 and 557.44 in the linear elastic, inelastic I and inelastic II regimes, respectively, for 0.1/0.5 wt% of CNT/GNP. This study demonstrates the fabrication method and the self-sensing performance of CNT/GNP/UHMWPE nanocomposites with improved properties useful for orthopedic implants.

In-situ preparation and characterization of ultra-high molecular weight polyethylene/diamond nanocomposites using Bi-supported Ziegler-Natta catalyst: Effect of nanodiamond silanization

In this study, reinforcement of ultra-high molecular weight polyethylene (UHMWPE) was investigated using the sol-gel surface modified diamond nanoparticles (NDs). Nanocomposite samples were synthesized via in-situ polymerization using bi-supported Ziegler-Natta catalyst. Fourier transform infrared spectroscopy, thermogravimetric analysis and contact angle measurements proved the proper silanization (∼1.9%) of NDs. Characterization of the catalysts revealed decrease in the activity of catalysts in presence of NDs which were responsible for the lower average molecular weight of the samples. Field emission scanning electron microscopy revealed an improved dispersion of the modified NDs in UHMWPE matrix by silanization. The incorporation of 2 wt.% unmodified and modified NDs enhanced the storage modulus (≤106% and ≤124%) and tensile strength (≤33% and ≤86%), respectively. Also, improvement in shore D and scratch hardness strength can be achieved in presence of NDs. Furthermore, tribological properties of the samples were investigated and discussed accordingly.

In situ fabrication of cellulose nanocrystal‐silica hybrids and its application in UHMWPE: Rheological, thermal, and wear resistance properties

Novel cellulose nanocrystal (CNC)‐silica (SiO2) nanohybrids with a better thermal stability were successfully fabricated by sol–gel method. In this unique hybrid architecture, it was found that silica particles were uniformly adsorbed/anchored by the CNC via covalent bonding and hydrogen bonding. Subsequently, the nanocomposites containing nanofillers (CNC‐SiO2 nanohybrids or CNC), ultrahigh molecular weight polyethylene (UHMWPE), polyethylene glycol (PEG), were prepared by the twin screw extrusion and their properties and structure were systematically investigated. With the incorporation of CNC‐SiO2 nanohybrids (or CNC) into the UHMWPE matrix, the tensile strength, flexural strength, flexural modulus, vicat softening temperature, and crystallinity of the ensuing nanocomposites were significantly increased. Meanwhile, the nanofiller could enhance the wear resistance of UHMWPE. Notably, compared to CNC, the unique beaded structure of CNC‐SiO2 nanohybrids could endow the UHMWPE with an overall superior performance. POLYM. COMPOS., 39:E1701–E1713, 2018. © 2017 Society of Plastics Engineers

Electrical properties of graphene nanoplatelets/ultra-high molecular weight polyethylene composites

Graphene nanoplatelets (GNPs)/ultra-high molecular weight polyethylene (UHMWPE) composites with a segregated structure had been fabricated using ethanol-assisted dispersion and hot compression at 180 °C. A percolation threshold of 3.5 wt% was achieved because of the formation conductive network. The positive temperature coefficient (PTC) and the negative temperature coefficient (NTC) effects of GNPs/UHMWPE composites had been investigated. The PTC behavior enhanced with increasing GNPs content but this was not always the case. The maximum PTC effect was observed in GNPs/UHMWPE composites (GNPs, 3.8 wt%) with the relatively low room temperature resistivity and the relatively high peak resistivity. The structure for GNPs/UHMWPE composites was examined by the SEM. The fact revealed that the slight interaction between GNPs and UHMWPE matrix may be changed by thermal cycles, and this can explain why thermal cycles could increase PTC and NTC intensity.

The Mechanical Properties and Modeling of Creep Behavior of UHMWPE/Nano-HA Composites

Composites with different levels of hydroxyapatite (HA) content and ultra-high molecular weight polyethylene (UHMWPE) were prepared in this work. Mechanical properties of the composites were examined here, and to evaluate the effect of HA particles on the time-dependent behavior of the pure matrix, the creep and recovery performance of composites at various stress levels were also researched. As expected, the addition of HA influenced the time-dependent response of the UHMWPE and the effect had a strong dependence on the HA content. The creep and recovery strain of the composites significantly decreased with increasing HA content, and tensile properties were also impaired, which was due to the concentration of HA fillers. The mechanism and effect of HA dispersed into the UHMWPE matrix were examined by scanning electron microscopy. Additionally, since variations in the adjusted parameters revealed the impact of HA on the creep behavior of the UHMWPE matrix, Findley’s model was employed. The results indicated that the analytical model was accurate for the prediction of creep of the pure matrix and its composites.

Ultrahigh molecular weight polyethylene composites with segregated nickel conductive network for highly efficient electromagnetic interference shielding

Conductive ultrahigh-molecular-weight polyethylene (UHMWPE) composite with segregated nickel (Ni) structure which exhibited highly efficient electromagnetic interference (EMI) shielding performance was fabricated in this work. By synthesizing nickel coated UHMWPE particles via electroless deposition and then hot compressing, the prearranged thin Ni layer could only selectively locate at the boundary between UHMWPE regions due to the specific high melting viscosity of UHMWPE, and thus constructed a well connected segregate Ni conductive network in UHMWPE matrix. Owing to the advantage of segregated network structure, the UHMWPE/Ni composite shows a low percolation threshold and high conductivity, and exhibits an EMI shielding effectiveness (SE) of average 55dB with Ni content of only 2.58vol% in X-band. This result indicates the segregated UHMWPE/Ni composite can serve as an ultra-efficient material for EMI shielding applications.

UHMWPE Hybrid Nanocomposites for Improved Tribological Performance Under Dry and Water-Lubricated Sliding Conditions

To tap the full potential of polymers to be used as tribo-materials under water lubrication, it is very important to improve their resistance to water uptake on the one hand and improve their strength and load bearing capacity on the other so that their performance under these conditions is not deteriorated. Hence, a unique approach of fabricating a hybrid polymer nanocomposite reinforced with nanoclay for improving the resistance to water uptake and carbon nanotubes (CNTs) to improve the mechanical/tribological properties is undertaken. Ultrahigh molecular weight polyethylene (UHMWPE) hybrid nanocomposites were fabricated via ball milling followed by hot pressing method. Functionalized multi-wall CNTs and C15A organoclay were used as nanofillers in UHMWPE matrix. Hybrid nanocomposites were developed with CNT loadings of 0.5, 1.5 and 3.0 wt% while keeping C15A organoclay content fixed at an optimized value of 1.5 wt%. Initially, the hybrid nanocomposites were optimized under dry sliding conditions whereby a loading of 1.5 wt% of CNTs and 1.5 wt% C15A organoclay resulted in the maximum reduction in the specific wear rate by about 64% as compared to pristine UHMWPE. Later, tribological performance of the optimized hybrid nanocomposite was compared with pristine UHMWPE and its UHMWPE nanocomposites under water-lubricated conditions sliding against a 440C stainless steel ball for 150,000 cycles. The specific wear rate showed a reduction by ~46% for the 1.5 wt% CNTs hybrid nanocomposites as compared to pristine UHMWPE under water lubrication. The improved resistance to wear was attributed to the uniform dispersion of both the nanofillers, namely CNTs and C15A organoclay which effectively increased the load bearing capacity of UHMWPE. Moreover, the excellent barrier properties of the platelet-like structure of C15A clay which presented a torturous path for the diffusion of the water molecule in UHMWPE reduced the softening of the surface layer leading to better resistance to wear under water lubrication.