Ultra-high Molecular Weight Polyethylene Films Research Articles

The effect of reserved shish content on the structural evolution of high-entanglement ultrahigh molecular weight polyethylene films during the hot stretching process

To explore novel approaches facilitating the structural evolution of high-entanglement ultrahigh molecular weight polyethylene (UHMWPE) films, this study precisely controlled the temperature during compression molding to successfully prepare high-entanglement UHMWPE films with different shish contents. Using in-situ small-angle X-ray scattering (SAXS)/ultra-small-angle X-ray scattering (USAXS)/wide-angle X-ray diffraction (WAXD) alongside ex-situ scanning electron microscopy (SEM) and differential scanning calorimetry (DSC), we investigated the influence of shish contents on the structural evolution of high-entanglement UHMWPE films during hot stretching. The results indicate that increasing shish content in high-entanglement UHMWPE films reduces the accumulation of inclined lamellar crystals caused by high entanglement, promoting the transformation of inclined lamellar crystals into shish-kebab crystals and facilitating the formation of more shish-kebab crystals. In high-entanglement UHMWPE films with high shish content, eventually, all inclined lamellar crystals even transform into shish-kebab crystals.

Structural Evolution of High-Entanglement Ultrahigh Molecular Weight Polyethylene Films with Reserved Shish Crystals during the Hot Stretching Process

Structural Evolution of High-Entanglement Ultrahigh Molecular Weight Polyethylene Films with Reserved Shish Crystals during the Hot Stretching Process

Anti-Ballistic Performance of PPTA/UHMWPE Laminates.

Poly(p-phenylene terephthalamide) (PPTA) and ultra-high-molecular-weight polyethylene (UHMWPE) are high-performance polymer materials largely used for body armor applications. Although composite structures from a combination of PPTA and UHMWPE have been created and described in the literature, the manufacture of layered composites from PPTA fabrics and UHMWPE films with UHMWPE film as an adhesive layer has not been reported. Such a new design can provide the obvious advantage of simple manufacturing technology. In this study, for the first time, we prepared PPTA fabrics/UHMWPE films laminate panels using plasma treatment and hot-pressing and examined their ballistic performance. Ballistic testing results indicated that samples with moderate interlayer adhesion between PPTA and UHMWPE layers exhibited enhanced performance. A further increase in interlayer adhesion showed a reverse effect. This finding implies that optimization of interface adhesion is essential to achieve maximum impact energy absorption through the delamination process. In addition, it was found that the stacking sequence of the PPTA and UHMWPE layers affected ballistic performance. Samples with PPTA as the outermost layer performed better than those with UHMWPE as the outermost layer. Furthermore, microscopy of the tested laminate samples showed that PPTA fibers exhibited shear cutting failure on the entrance side and tensile failure on the exit side of the panel. UHMWPE films exhibited brittle failure and thermal damage at high compression strain rate on the entrance side and tensile fracture on the exit side. For the first time, findings from this study reported in-field bullet testing results of PPTA/UHMWPE composite panels, which can provide important insights for designing, fabricating, and failure analysis of such composite structures for body armors.

The effect of temperature on the structural evolution of ultra-high molecular weight polyethylene films with pre-reserved shish crystals during the stretching process

The influence of temperature on the structural evolution and macroscopic properties of ultrahigh-molecular weight polyethylene (UHMWPE) films with pre-reserved shish crystals during stretching was investigated by in-situ small-angle X-ray scattering (SAXS)/wide-angle X-ray diffraction (WAXD) measurements as well as ex-situ differential scanning calorimetry (DSC) and scanning electron microscopy (SEM) measurements. The UHMWPE films with pre-reserved shish crystals were obtained by compression molding at 135 °C and further stretched at different temperatures of 100, 110, 120 and 130 °C. At all stretching temperatures, the pre-reserved shish can promote the structural evolution of UHMWPE films to form shish-kebab or shish crystals. At 100, 110, and 120 °C, the two-point pattern can be observed for 2D-WAXD, the lamellar crystals fragment to form shish-kebab crystals by epitaxial crystallization on pre-reserved shish crystals. At 130 °C, the two-point pattern signal becomes weak at 2D-WAXD, the lamellar crystals are mainly melted and then recrystallized on the pre-reserved shish crystals to form large-period kebab crystals. Moreover, the temperature of 130 °C favors the growth of kebab crystals with larger lateral size, resulting in a difficult transformation to shish crystals. In addition, at 110 and 120 °C, the crystallinity and orientation of UHMWPE films increase significantly after stretching, resulting in improved mechanical properties.

Dielectric polymer composites with ultra-high thermal conductivity and low dielectric loss

Polymer based dielectric materials with simultaneously high thermal conductivity and low dielectric loss are highly desirable in various applications like energy storage, thermal management and electronic packaging. Polymer dielectrics generally benefit from good electrical insulation, high breakdown strength, high toughness and low density but suffer from very low thermal conductivity (0.1–0.5 W m −1 K −1). Herein we propose a new strategy to overcome this compromise; solid-state drawing of ultra-high molecular weight polyethylene (UHMWPE) films doped with a small amount of nanodiamonds (NDs). The resulting orientation of UHMWPE macromolecules and the nanofiller significantly improves the thermal conductivity along the stretching direction, while the dodecane surface functionalization of the NDs endows a robust interface between the matrix and filler, which minimizes the thermal resistance and dielectric loss. Our composites film (2 wt% NDs) shows an ultra-high thermal conductivity of 60 W m −1 K −1 in the drawing direction and very low dielectric loss, both at low and high electric field. More generally, herein we demonstrates that the interfaces introduced by the nanofillers do not necessarily cause an increase in dielectric loss at high electric field and a decrease in thermal conductivity, providing a new direction for the design of novel polymer based dielectric and functional materials.

Corrosion resistance improvement of the Ti6Al4V/UHMWPE systems by the assembly of ODPA molecules by dip coating technique

Living with degenerative diseases, such as arthritis and osteoporosis, is challenging if orthopedic devices manifest adverse effects caused by corrosion processes. Ti6Al4V alloy is used to manufacture orthopedic implants due to its excellent mechanical and osseointegration properties. Nonetheless, it has poor resistance to wear and corrosion by biological fluids and mechanical activity. This degradation process generates the need to improve the corrosion resistance of metallic biomaterials used as biomedical implants. Dip-coating technique is a wet coating method used to lessen wear damage on the metal surface and can produce coatings using a wide variety of molecules at a low cost. In this work, Ti6Al4V alloys were coated with ultra-high molecular weight polyethylene (UHMWPE) and Octadecylphosphonic Acid (ODPA) films forming a UHMWPE/ODPA bilayer coating by dip-coating method to improve protection efficiency against corrosion in phosphate-buffered isotonic saline solutions and proposed it as alternative coatings to delay the failure of medical implants. The optimization of individual coated systems were obtained with an immersion time of 40 s (Ti6Al4V/UHMWPE) and 30 h (Ti6Al4V/ODPA) with corrosion current densities of 1.51 × 10−9 A cm−2 and 6.8 × 10−8 A cm−2, respectively. The formation of bilayer coatings reduces the average roughness from 19.34 nm (Ti6Al4V/UHMWPE) to 12.67 nm (Ti6Al4V/UHMWPE/ODPA). ODPA deposition on UHMWPE films changes the corrosion rate by interfering with the anodic and cathodic reactions, reducing the corrosion rate to 7.46 × 10−4 μm y−1 and an estimated corrosion protection efficiency of about 99.99 %. The results show a superior performance as a protective barrier over the individual films (1.19 μm y−1 with 97.2 %, and 0.026 μm y−1 with 99.9 %, ODPA, and UHMWPE, respectively), improving the corrosion resistance of the Ti6Al4V alloys.

Influence of Prereserved Shish Crystals on the Structural Evolution of Ultrahigh-Molecular Weight Polyethylene Films during the Hot Stretching Process

Influence of Prereserved Shish Crystals on the Structural Evolution of Ultrahigh-Molecular Weight Polyethylene Films during the Hot Stretching Process

Origin of high thermal conductivity in disentangled ultra-high molecular weight polyethylene films: ballistic phonons within enlarged crystals

The thermal transport properties of oriented polymers are of fundamental and practical interest. High thermal conductivities ( ≳ 50 Wm−1K−1) have recently been reported in disentangled ultra-high molecular weight polyethylene (UHMWPE) films, considerably exceeding prior reported values for oriented films. However, conflicting explanations have been proposed for the microscopic origin of the high thermal conductivity. Here, we report a characterization of the thermal conductivity and mean free path accumulation function of disentangled UHMWPE films (draw ratio ~200) using cryogenic steady-state thermal conductivity measurements and transient grating spectroscopy. We observe a marked dependence of the thermal conductivity on grating period over temperatures from 30–300 K. Considering this observation, cryogenic bulk thermal conductivity measurements, and analysis using an anisotropic Debye model, we conclude that longitudinal atomic vibrations with mean free paths around 400 nanometers are the primary heat carriers, and that the high thermal conductivity for draw ratio ≳ 150 arises from the enlargement of extended crystals with drawing. The mean free paths appear to remain limited by the extended crystal dimensions, suggesting that the upper limit of thermal conductivity of disentangled UHMWPE films has not yet been realized.

Fabrication of light‐weight ultrahigh molecular weight polyethylene films with hybrid porous structure and the thermal insulation properties

AbstractAccording to the infrared stealth mechanism, controlling the surface temperature of objects can effectively hide the infrared radiation and resist the infrared detection. In this paper, a high infrared transparent polymer ultrahigh molecular weight polyethylene (UHMWPE) is selected as the matrix of a thermal insulation material. UHMWPE porous films with high porosity and hybrid pore structure are obtained through the thermal induced phase separation combining with particle leaching method. The film structures with micropores and macropores are adjusted through the variation of the mass ratio of UHMWPE/liquid paraffin, the dosage and the particle size of NaCl. The thermal conductivity of the UHMWPE film is as low as 0.034 W/(m K), while the density is only 54.4 mg/cm3. The classical Maxwell‐Eucken model is used to discuss the relationship between the pore structure and the thermal conductivity of the films. It is determined that the hybrid porous structure can reduce heat conduction and gas–solid coupling effect simultaneously, thus the thermal conductivity is significantly reduced. Moreover, the porous films exhibited remarkable flexibility and hydrophobicity. Based on these properties, the porous films are highly promising in the field of thermal insulation protection and infrared stealth.

Preparation of a Novel UHMWPE Lithium Battery Separator by Electrospraying Method

In this paper, an ultra high molecular weight polyethylene (UHMWPE) lithium ion battery composite separator was successfully prepared via the electrospraying technique. First, the optimal electrospraying parameters of Polyvinylidene fluoride (PVDF), mass fraction of PVDF 3wt% and electrospraying voltage 21kV, were successfully determined by adjusting the effect of voltage and concentration of PVDF solution. Then the composite separator was prepared by electrospraying PVDF particles on the UHMWPE film. Finally the porosity rate, thermal stability and charge and discharge properties of the separator were analyzed. The analytical results show that the porosity rate of the composite separator is increased from 46.5% to 73.1%, and the heat shrinkage of the separator in the longitudinal is reduced from 2.6% to 1.3%. The first specific discharge capacity of the composite separator increases by 5.8%, and the separator has a good cycle stability after 50 cycles.

Enhanced in-plane thermal conductivity of ultrahigh molecular weight polyethylene films via a new design of a two-step biaxial stretching mode

Enhanced in-plane thermal conductivity of ultrahigh molecular weight polyethylene films via a new design of a two-step biaxial stretching mode

Improving Interlayer Adhesion of Poly(p-phenylene terephthalamide) (PPTA)/Ultra-high-molecular-weight Polyethylene (UHMWPE) Laminates Prepared by Plasma Treatment and Hot Pressing Technique.

Poly(p-phenylene terephthalamide) (PPTA) is a high-performance polymer that has been utilized in a range of applications. Although PPTA fibers are widely used in various composite materials, laminar structures consisting of PPTA and ultra-high-molecular-weight polyethylene (UHMWPE), are less reported. The difficulty in making such composite structures is in part due to the weakness of the interface formed between these two polymers. In this study, a layered structure was produced from PPTA fabrics and UHMWPE films via hot pressing. To improve the interlayer adhesion, oxygen plasma was used to treat the PPTA and the UHMWPE surfaces prior to lamination. It has been found that while plasma treatment on the UHMWPE surface brought about a moderate increase in interlayer adhesion (up to 14%), significant enhancement was achieved on the samples fabricated with plasma treated PPTA (up to 91%). It has been assumed that both surface roughening and the introduction of functional groups contributed to this improvement.

Gamma Rays Induced Modification in Ultrahigh Molecular Weight Polyethylene (UHMWPE)

Modifications taking place in ultrahigh molecular weight polyethylene (UHMWPE) films due to gamma ray radiation-induced and investigated in correlation with the applied doses. Films were irradiated in a vacuum at room temperature by a 1.25 MeV Co60 a source with doses ranging from 0 to 300 kGg. The optical, chemical, structural, and surface morphological properties of the irradiated and unirradiated UHMWPE films were investigated by UV-Visible, FTIR, XRD, and SEM, respectively. The band gap E g decreases with increasing radiation dose and coloration effects have been seen at higher doses. FTIR spectra show an oscillatory behavior in the transmittance intensities without affecting in their peak positions. Number of small absorption peaks can be seen clearly which may be due to the cross-linking of the polymeric chain. No significant change in crystalline peak has been found in the X-ray diffraction pattern indicating the structural stability of the polymer. The morphology of the smooth topography of the polymer samples to change rougher one polymeric sample shows the formation of microvoids on the surface of the polymeric materials with the increase of the doses from 0 to 300 kGy.

NIR-vis-UV Light-Responsive High Stress-Generating Polymer Actuators with a Reduced Creep Rate.

Untethered, light-responsive, high-stress-generating actuators based on widely-used commercial polymers are appealing for applications in soft robotics. However, the construction of actuators that are stable and reversibly responsive to low-intensity ultraviolet, visible, and infrared lights remains challenging. Here, transparent, stress-generating actuators are reported based on ultradrawn, ultrahigh molecular weight polyethylene films. The composite films have different draw ratios (30, 70, and 100) and contain a small amount of graphene in combination with ultraviolet and near-infrared-absorbing dyes. The composite actuators respond rapidly (t0.9 <0.8 s) to different wavelengths of light (i.e., 780, 455, and 365nm). A maximum photoinduced stress of 35MPa is achieved at a draw ratio of 70 under near-infrared light irradiation. The photoinduced stress increases linearly with the light intensity, indicating the transfer of light into thermally induced mechanical contraction. Moreover, the addition of additives lead to a reduction in the plastic creep rate of the drawn films compared to their nonmodified counterparts.

Electrochemical Performance of UHMWPE Biocompatible Coatings on Ti6Al4V Alloy in Simulated Body Solutions: Influence of Immersion Time

Ti6Al4V alloys are widely employed in the production of orthopedic implants due to their adequate mechanical properties, corrosion resistance, and biocompatibility. Nevertheless, these alloys present a high friction coefficient and low wear resistance limiting their half-life time. Then, once implanted, the interaction between the metal and the surrounding tissue can promote the corrosion process which in turn can ultimately trigger its rejection. In this work, ultra-high molecular weight polyethylene (UHMWPE) films were coated onto Ti6Al4V alloy substrates using the dip coating method to evaluate the influence of immersion time on the electrochemical performance in Simulated Body Solutions. The coating thickness was ranged from 11-20 µm changing the immersion time between 20 and 40 s. Structural characterization shows that an increase in the immersion time reduces the crystallinity of UHMWPE coatings and their porosity from 32 to 0.2%. The performance of the films as protective barriers against the corrosion process was enhanced with high immersion times, decreasing the corrosion rate up to 0.05 µm y-1 (40 s).

Shish-Kebab-Structured UHMWPE Coating for Efficient and Cost-Effective Oil-Water Separation.

High-performance low-cost superhydrophobic sponges are desired for selective recycling of leaking oils from open water. Herein, an ingenious method is proposed to fabricate an ultrathin superhydrophobic coating layer on a commercial sponge. The coating layer is composed of a shish-kebab-structured porous ultrahigh molecular weight polyethylene (UHMWPE) film that is fabricated from a UHMWPE/xylene solution by shear flow-induced crystallization. A strong relationship between the shish-kebab crystallite morphology and the superwetting performance is confirmed. The UHMWPE coating layer fabricated at a 900 rpm rotation rate possesses a lamellae size of 95.1 nm and a lamellae distance of 27.4 nm, which lead to a high water contact angle of 157° and a low contact angle hysteresis of 4.5°. The UHMWPE layer prepared in 4 min of treatment is thick enough to prevent the intrusion of water even under vacuum and remain superoleophilic. The developed UHMWPE-coated sponge (UCS) exhibited a high absorption capability of 70-191 g/g toward various oils and solvents, which is comparable with the neat melamine sponge. Its excellent compressibility and durability enabled fast recovery of absorbed oil with a high recovery rate (over 85%) by mechanical squeezing. The UCS could be assembled into small devices to selectively collect oil from open water and a water/oil mixture using a pump, which manifests its promising practical applicability. Apart from these extraordinary properties, the approach developed has the lowest material cost and the shortest processing time hitherto.

A New Approach Based on Glued Multi-Ultra High Molecular Weight Polyethylene Forms to Fabricate Bone Replacement Products.

Three types of glue based on thiol-ene reaction, polyvinyl alcohol (PVA)/cellulose, and phenol formaldehyde were prepared and applied on modified ultra-high molecular weight polyethylene (UHMWPE) samples grafted by cellulose. In comparison with unmodified UHMWPE samples, T-peel tests on the modified and grafted UHMWPE films showed an increase in the peel strength values for the glues based on thiol-ene reaction, PVA/cellulose, and phenol formaldehyde by 40, 29, and 41 times, respectively. The maximum peel strength value of 0.62 Kg/cm was obtained for the glue based on phenol formaldehyde. Mechanical tests for the cylindrical multi-UHMWPE forms samples, made of porous UHMWPE as a trabecular layer and an armored layer (cortical layer) that consists of bulk and UHMWPE films, indicated an improvement in the mechanical properties of these samples for all glue types, as a result of the UHMWPE films existence and the increase in the number of their layers. The maximum compressive yield strength and compressive modulus values for the armored layer (bulk and six layers of the UHMWPE films using the glue based on thiol-ene reaction) were 44.1 MPa (an increase of 17%) and 1130 MPa (an increase of 36%), respectively, in comparison with one armored layer of bulk UHMWPE. A hemocompatibility test carried out on these glues clarified that the modified UHMWPE grafted by cellulose with glues based on PVA/cellulose and thiol-ene reaction were classified as biocompatible materials. These multi-UHMWPE forms composites can be considered a promising development for joint reconstruction.

The Structural and Mechanical Properties of the UHMWPE Films Mixed with the PE-Wax.

Since obtaining a highly oriented structure based on a large-scale commercial ultra-high molecular weight polyethylene (UHMWPE) is considered very difficult due to its high molecular weight and melting index, modifying the structure of these cheap commercial UHMWPE brands into a supra-molecular structure with fiber-forming properties by adding a small amount of polyethylene wax (PE-wax) will provide the possibility to obtain highly oriented UHMWPE products with enhanced mechanical and tribological properties. In this work, highly oriented UHMWPE/PE-wax films were prepared. The PE-wax affected the UHMWPE as an intermolecular lubricant. The obtained lamellar structure of the UHMWPE/PE-wax composites had a better processability. The UHMWPE and UHMWPE/PE-wax structures for the xerogels and the films were studied by using differential scanning calorimetry and scanning electron microscopy. The PE-wax presence enhanced the mechanical properties of the UHMWPE/PE-wax films to a high degree. The highest average value of the tensile strength was 1320 MPa (an increase of 78%) obtained by adding a PE-wax content of 1.0 wt.%, and the highest average value of the Young’s modulus was 56.8 GPa (an increase of 71%) obtained by adding a PE-wax content of 2.0 wt.%. The addition of the PE-wax increased the work of fracture values of the UHMWPE/PE-wax films up to 233%. The formation of the cavities was observed in the virgin UHMWPE films more than in the UHMWPE/PE-wax films, and the whitening of the oriented films was related to the crystallization process more than to the cavitation phenomenon. The coefficient of friction of the oriented UHMWPE/PE-wax films improved by 33% in comparison with the isotropic UHMWPE, and by 7% in comparison with the oriented virgin UHMWPE films.

Fast, Light-Responsive, Metal-Like Polymer Actuators Generating High Stresses at Low Strain

Summary Producing lightweight polymeric actuators able to generate high stresses typical of hard metals and/or ceramics remains challenging. The photo-mechanical responses of ultra-drawn ultra-high molecular weight polyethylene (UHMWPE) actuators containing azobenzene photo-switches with symmetrically attached polyethylene (PE) side chains are reported. Long PE side chains promote dispersion within the apolar UHMWPE matrix, and the ultra-drawn films are highly aligned. The ultra-drawn azobenzene-doped UHMWPE films have high Young's moduli (∼100 GPa) and are viscoelastic at room temperature at strains below 1%. The photo-mechanical response of the films is fast ( 6 × 104 Pa (kg m−3)−1) to UV or visible light at a low strain (∼0.06%). The actuator responds to rotating linearly polarized light, causing a photo-induced stress wave response. Such rapid, high-stress, low-strain, photo-mechanical responses are unique in soft polymer systems with physical values approaching hard metals/ceramics.

Studying the surface of UHMWPE films modified with graphene nanoplatelets using a Raman mapping method

This article discusses the nature of the distribution of intact polyaniline-functionalized graphene nanoplatelets (GNPs) in the surface layer of nanomodified films of ultra-high molecular weight polyethylene (UHMWPE) using a Raman mapping method. On the Raman maps, D, G, and 2D peaks can be observed for the 0.1 wt.% GNPs content in the UHMWPE. In the surface layer of the films containing 1.0 wt.% GNPs, these signals are not detected, thereby indicating the displacement of the nanomodifier into the polymer bulk. In contrast, the polyaniline-functionalized GNPs tend to migrate to the surface of the UHMWPE nanocomposite film and evenly distribute in the surface layer as the concentration increases from 0.1 to 2.0 wt.%.