Addition Of Ultrahigh Molecular Weight Polyethylene Research Articles

Effects of UHMWPE Filler on the Tribological and Mechanical Properties of Biocompatible Epoxies

The effects of ultra-high-molecular-weight polyethylene (UHMWPE) as a filler on the tribological and mechanical properties of two biocompatible epoxies were studied. SU-8 and Structalit 8801 (a trade name) were the two biocompatible epoxies selected for this investigation. UHMWPE powder (40–48 μm particle size) was added to the selected epoxies to tailor their mechanical and tribological properties. In dry sliding tests, after adding 25 wt% of UHMWPE particles, the coefficient of friction (COF) was reduced by 79 and 67% for SU-8 and Structalit, respectively, and the specific wear rate was reduced by 92 and 58% for SU-8 and Structalit, respectively. Fourier transform infrared (FTIR) analysis conducted on the samples indicated that there was no chemical bonding between UHMWPE fillers and the epoxy matrices. A biocompatibility test conducted on SU-8 cured with the hardener confirmed that the samples were not cytotoxic. In addition, it was noted that the ductility ratio of SU-8 and Structalit increased by 71 and 40%, respectively, with the addition of UHMWPE. These novel composites can find applications as biomaterials for tribologically demanding applications such as hip–knee joint implants, dental implant, etc.

Tailoring the crystalline morphology and mechanical property of olefin block copolymer via blending with a small amount of UHMWPE

In this study, the crystalline morphology and mechanical property of Olefin Block Copolymer (OBC) were tailored by adding a small amount (up to 10 wt%) of ultrahigh molecular weight polyethylene (UHMWPE). To do this, OBC and UHMWPE was solution blended first and then subjected to compression molding or injection molding, respectively. It was found that a small quantity of UHMWPE (0.5 wt%, 1 wt%) can be fully mixed with OBC, while phase separation occurs when UHMWPE content is higher than 2.5 wt%, as suggested by SEM and DSC results. For compression molded samples, an obvious increase of Young's modulus from 12 MPa to 22 MPa while maintaining the good elasticity of OBC was observed as the content of UHMWPE is less than 2.5 wt% (in the phase miscible range). With further increasing of UHMWPE content to 10 wt%, only slightly increased Young's modulus is seen. Thus the miscibility between OBC and UHMWPE plays an important role in determining the mechanical property for compression molded samples. However, a continuous increase of Young's modulus was observed with the increase of UHMWPE content for samples obtained via injection molding, with a slight increase (from 23 MPa to 40 MPa) as the content of UHMWPE is less than 2.5 wt%, while with a large increase (from 40 MPa to 156 MPa) as the content of UHMWPE increases from 2.5 wt% to 10 wt%, accompanied with a greatly decrease of elongation (from 1100% to 50%). Even elastomer-to-plastic transition takes place when the content of UHMWPE is large (5 wt%, 10 wt%). Structural analysis of injection-molded samples shows that shish-kebab-like structures can be successfully induced as addition of UHMWPE along with gradually increased crystal orientation. It was interesting to find that small-addition of UHMWPE favors increased tie-effect due to the miscibility between OBC and UHMWPE, which is helpful to the elasticity retaining as well as strength enhancement, while large-addition of UHMWPE gives rise to phase separation and mixed shish-kebabs (OBC/UHMWPE hybrid shish-kebabs and UHMWPE homo-shish-kebabs), leading to elastomer-to-plastic transition.

Effect of Ultra High Molecular Weight Polyethylene (UHMWPE) as Binder and Sintering Temperature in Kaolin Geopolymer Ceramics on Flexural Strength

This paper present the flexural strength of kaolin geopolymer ceramics with addition of ultra-high molecular weight polyethylene (UHMWPE) as a binder. The effect of varying UHMWPE loading and different sintering temperature on kaolin geopolymer ceramics were evaluated. Kaolin and alkaline activator were mixed with the solid-to-liquid ratio of 1.0. Alkaline activator was formed by mixing the 8 M NaOH solution with sodium silicate at a ratio of 0.24. Addition of UHMWPE to the kaolin geopolymer ceramics are fabricated with UHMWPE loadings of 2, 4, 6 and 8 (wt. %) by using powder metallurgy method. The samples were heated at different temperature started from 900 °C until 1200 °C and the strength were tested. It was found that the flexural strength for the kaolin geopolymer ceramics with addition of UHMWPE were higher and generally increased with the increasing of UHMWPE loading. Similar trend was observed for the effect of sintering temperature. The result revealed that the optimum flexural strength was obtained at UHMWPE loading of 8 wt. % and the samples heated at 1200 °C achieved the highest flexural strength (49.15 MPa).

Stratiform β crystals in ultrahigh molecular weight polyethylene and β-nucleating agent-nucleated isotactic polypropylene at micro-injection molding condition

The crystalline and oriented morphologies of isotactic polypropylene (iPP), ultrahigh molecular weight polyethylene (UHMWPE) and β-nucleating agent (β-NA) blends molded by micro-injection were investigated via polarized light microscopy, scanning electron microscopy, differential scanning calorimetry and wide-angle X-ray diffraction. The results showed that the addition of β-NA raised the onset crystallization temperature and the relative crystallinity of the β crystals of the micro-injection molding (MIM) specimens because of its strong heterogeneous nucleating effect in the iPP matrix. The introduction of UHMWPE, because of its “maintaining-orientation” effect, increased the thickness of the shish–kebab structure in the skin layer and induced the formation of perfect β cylindrulites that are epiphytic and symmetrical on the surface of long fibrous crystals. Furthermore, stratiform β crystals induced by the combined effects of strong shear flow field and addition of UHMWPE and β-NA were observed and investigated. Such a unique structure provides an effective way to tune the mechanics of MIM parts.

Role of Ultrahigh Molecular Weight Polyethylene during Rotation Extrusion of Polyethylene Pipe

A small amount of ultrahigh molecular weight polyethylene (UHMWPE) was added to a PE matrix that was then processed into a pipe by a self-designed rotation extrusion system. The results showed that during the rotation extrusion of the PE pipe, the polymer melts helically moved forward in an off-axis direction to induce molecular orientation and shish-kebab alignment deviate from the axial direction. However, because of sufficient relaxation of oriented molecules at high temperature, numerous spherulites arose in the pure PE pipe. With the addition of UHMWPE, the flow character of the PE matrix was tailored so the molecular relaxation was suppressed and the flow effect on formation of shish-kebab was amplified, bringing about denser shish-kebabs off the axial direction in the PE pipe. As a result, a PE pipe with excellent resistance to slow crack growth was prepared.

Improved performance balance of polyethylene by simultaneously forming oriented crystals and blending ultrahigh-molecular-weight polyethylene

Polyethylene as a versatile polymer is being increasingly used for parts whose surfaces are in contact with moving metallic components or solid particles. This needs polyethylene to be greatly improved in mechanical properties as well as wear resistance. To this end, in the current work, various contents of ultrahigh-molecular-weight polyethylene (UHMWPE) were added into high-density polyethylene (HDPE) for enhancement of wear resistance, while the oriented crystals, i.e., shish-kebabs, were induced by shear flow for mechanical reinforcement. With 30 wt% UHMWPE was added, highly improved performance balance was achieved. The tensile strength rose from 26.4 MPa for normal HDPE samples to 68.5 MPa for the modified HDPE blends. The same trend was observed for impact toughness, where the impact strength increased from 6.3 to 34.1 kJ m−2. Moreover, addition of UHMWPE could reduce the wear rate from 22.1 to 7.6 mg MC−1. A very interesting phenomenon was observed, in which the overall properties of the modified HDPE blends were constantly enhanced with the increase of UHMWPE content though UHMWPE itself does not have much better mechanical properties than the oriented HDPE. This was ascribed to the amplified shear effect as a result of UHMWPE addition. The exceptionally high melt viscosity of UHMWPE assumes a gel state even at high temperature, making it just deform and hardly flow under the shear field, which amplifies the flow velocity difference between UHMWPE phase and HDPE melt. The amplified shear effect resulted in more pronounced molecular orientation and thus formation of a higher content of shish-kebab microstructure. Our work indicated that the melt processing-structure control strategy can desirably manipulate polyethylene products with desired properties.

The toxic and environmental evaluation of pyrolytic liquids by Allium cepa test

In this study, liquid products obtained from the pyrolysis of hazelnut shell (HS), with and without ultra-high molecular weight polyethylene (UHMWPE), were subjected to the Allium cepa test system. Pyrolysis in conjunction with the A. cepa test is a promising technology not only from the perspective of energy savings and a source of precious material, but in terms of the removal of hazardous material from the environment in safe manner. Dosages of pyrolytic liquids dissolved in water were determined according to lethal dose (LD50), with three different solution concentrations. The preparates were dyed with acetocarmine. The mitotic index decreased and chromosomal aberration, especially stickiness and c-mitosis, increased with dosage and time. The addition of UHMWPE to HS in the pyrolysis process resulted in less harmful chemical agents, as observed by the relatively higher mitotic index and lower levels of chromosomal aberration.

Crystallization behavior and foaming properties of polypropylene containing ultra‐high molecular weight polyethylene under supercritical carbondioxide

AbstractIn this study, a systematic investigation on the nonisothermal crystallization kinetics of conversional polypropylene (PP) containing various amounts of ultra‐high molecular weight polyethylene (UHMWPE) was reported, and the effects of UHMWPE on crystallization behavior of these PP materials and their foaming properties were also presented. The kinetic studies revealed that the incorporation of UHMWPE into PP led to an increase in the crystallization temperature and temperature range during the crystallization process as well as the relative crystallinity. This behavior was attributed to a comprehensive effect of the nucleation and entanglement of the UHMWPE chains. The kinetic models based on Ozawa's and Mo's methods were used to analyze the nonisothermal crystallization behaviors. It was found that the latter succeeded in describing the nonisothermal crystallization behavior of the PP containing UHMWPE, while the former was not appropriate. The activation energy for the nonisothermal crystallization determined by Kissinger's method also indicated that the crystallization ability of PP was improved with the addition of UHMWPE. Owing to the modification of the crystallization kinetics of the PP materials by introduction of UHMWPE, the foaming properties (i.e., cell uniformity and expandability etc.) were improved significantly. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

Friction and sliding wear of UHMWPE modified cotton fibre reinforced polyester composites

Ultrahigh molecular weight polyethylene (UHMWPE) modified polyester-cotton composites were developed and studied for friction and sliding wear behaviour at different applied loads and UHMWPE concentrations. Sliding wear tests were conducted by using pin-on-disc apparatus. Composites in the form of the pin were tested against EN-24 steel disc. The specific wear rate of polyester reduced on reinforcement of cotton and on addition of UHMWPE. The coefficient of friction of polyester resin increased on cotton reinforcement and reduced significantly on addition of UHMWPE in cotton polyester composite. The composites exhibited reductions in specific wear rate against the normal load in the specimens those containing 7.41 or higher volume percent of UHMWPE. The significant reduction in wear rate of UHMWPE modified polyester-cotton composite has been discussed with the help of SEM observations of worn surfaces and coefficient of friction. The addition of 14.19 vol.% UHMWPE in polyester resin brought down the value of μ to nearly half to that of polyester resin and 1/3rd of cotton polyester composite.

Sliding wear of PP/UHMWPE blends: effect of blend composition

In the present investigation, a wear resistant polymer, ultra high molecular weight polyethylene (UHMWPE) was melt blended with isotactic polypropylene (PP) in different proportions. Sliding wear tests were conducted by using Cameron Plint pin-on-disc apparatus. Polymer samples in the form of the pin were tested against EN-24 steel disc at different pressures and sliding speeds. The wear volume of PP reduces significantly on the addition of UHMWPE. At 0.28 m/s sliding speed, wear rate of PP was 15×10 −12 m 3/m which reduces to 0.28×10 −12 m 3/m on addition of 15 wt.% of UHMWPE. At 1.09 m/s sliding speed, PP deforms, while 15 wt.% of UHMWPE sample does not show significant deformation. Wear loss of 15 wt.% UHMWPE filled PP blend significantly low as compared to PP. Reduction in wear loss of UHMWPE filled PP blend has been attributed to the reduction in temperature of contact surface. Worn surface of the test sample showed two distinct morphological regions.

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

Elongational flow and birefringence of low density polyethylene and its blends with ultrahigh molecular weight polyethylenet

Via elongational flow opto-rheometry (EFOR), simultaneous measurements of tensile stress σ(t) and birefringence Δn(t) were conducted on a low density polyethylene (LDPE) melt and its blends with an ultra-high molecular weight polyethylene (UHMWPE) at 140°C under transient elongational flow with constant tensile strain rate ʵ0. The transient elongational viscosity nE(t)σ0 of LDPE melt first gradually increases with time t following the linear viscoelasticity rule in that ηE(t) is 3 times the shear viscosity development. 3η(t), at low shear rate γ up to a certain critical strain, beyond which ηE(t) tended to increase rapidly with t. The behaviour was often referred to as strain-induced hardening. For LDPE melt both σ(t) and Δn(t) versus tensile strain ɛ(t) (=ɛ0 t)curves were dependent on ɛ0 in such a manner that the stress optical coefficient C(t) ≡ Δ(t)/σ(t)) was independent either of ɛ0, ɛ(t), ɛ(t) or σ(t). Addition of UHMWPE up to 10 wt% to LDPE melt increased the levels of both σ(t) and Δn(t), but the tendency of strain-induced hardening was reduced. The C(t) was again independent either of ɛ0, ɛ(t) or σ(t) and also essentially independent of molecular weight (MW) and its distribution (MWD) or the blend ratio. For both LDPE and the blends the C(t) value roughly agreed with that (= 2.2 × 10−9 Pa−1) reported for shear flow experiments, thus confirming the val dity of the so far established stress optical rule.