Carbon nanofibre‐reinforced ultrahigh molecular weight polyethylene for tribological applications

Carbon nanofibre (CNF)‐reinforced ultrahigh molecular weight polyethylene (UHMWPE) nanocomposites containing up to 10 wt % of nanofibres were prepared by a novel solvent‐assisted extrusion process using short chain oligomers to tailor the melt viscosity of the UHMWPE matrix. A detailed investigation of the resulting nanocomposite microstructure and of the static mechanical properties revealed that the carbon nanofibres lead to improved mechanical properties of the UHMWPE related to the wear performance of such systems. Unidirectional sliding tests against a 100Cr6 steel under dry conditions verified the significant potential of dispersed carbon nanofibres to reduce the wear rate of this polymer. In light of the promising results, a further optimization of the processing conditions of such UHMWPE nanocomposites is expected to yield interesting future nanocomposite materials even for demanding applications such as artificial knee implants. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 4173–4181, 2007     

HIPS/γ‐irradiated UHMWPE/carbon black blends: Structuring and enhancement of mechanical properties

CB‐containing HIPS/UHMWPE and HIPS/XL‐UHMWPE are unique systems, in which structuring takes place, affecting the electrical (to be described in a future article), rheological, mechanical, and dynamical‐mechanical properties. The XL‐UHMWPE particles have undergone structural fixation due to the crosslinking, maintaining their porosity and internal intricate structure even after high‐temperature melt processing, as opposed to the UHMWPE particles. Differences in the flow mechanisms of HIPS/UHMWPE and HIPS/XL‐UHMWPE blends have been attributed to polymer viscous flow in the former case vs. particle slippage in the latter. The mechanical properties of HIPS/UHMWPE are enhanced when utilizing XL‐UHMWPE as a dispersed phase, especially the strength, because of changes in the inherent properties of the UHMWPE following irradiation, and in particular, the nature of the HIPS/XL‐UHMWPE interface. The results for the CB‐containing 70HIPS/30XL‐UHMWPE blend are especially surprising and of practical importance, due to the fact that no degradation of the mechanical properties has occurred as a result of the CB incorporation. The dynamical mechanical properties reflect the differences between the UHMWPE and XL‐UHMWPE‐containing blends as well. The presence of either type of UHMWPE, CB content, and blend composition affect the dissipation, but have only a minor influence on the transition temperatures of the components. Of special interest is the increased damping of XL‐UHMWPE–containing compositions. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 1731–1744, 1999     

Mechanical behavior,microstructure and thermooxidation properties of sequentially crosslinked ultrahigh molecular weight polyethylenes

The aim of this study was to explore the impact of the sequential irradiation and annealing process on the microstructure, thermooxidation behavior and mechanical properties of GUR 1050 ultrahigh molecular weight polyethylene (UHMWPE) with respect to the postirradiation annealed material. For this purpose, the effects of a variety of irradiation and annealing conditions on microstructure and mechanical properties were investigated. Differential scanning calorimetry was performed to characterize melting temperature, crystalline content and crystal thickness, whereas transmission electron microscopy provided additional insights into crystal morphology. Thermogravimetric experiments in air served to assess thermooxidation resistance and changes associated to radiation‐induced crosslinking. Fatigue properties were studied from three different approaches, namely short‐term cyclic stress–strain tests, long‐term fatigue experiments and crack propagation behavior. Likewise, three experimental techniques (uniaxial tensile test, impact experiments, and load to fracture of compact tension specimens) allowed evaluation of the fracture resistance. The present findings confirm sequentially crosslinked UHMWPE exhibited improved thermooxidation resistance and thermal stability compared to post‐irradiation annealed UHMWPE. Also, the mechanical behavior, including the fatigue and fracture resistance, of these materials was generally comparable regardless of the annealing strategy. Therefore, the sequential irradiation and annealing process might provide higher oxidation resistance, but not a significant improvement in mechanical properties compared to the single radiation dose and subsequent annealing procedure. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Effect of high‐energy ball milling on the structure and mechanical properties of ultra‐high molecular weight polyethylene

The structure and properties of ultrahigh‐molecular‐weight polyethylene (UHMWPE) powder after severe deformation processing in a planetary ball mill were studied by means of scanning electron microscopy, differential scanning calorimetry, and X‐ray analysis. We found that the severe deformation processing of UHMWPE changed the morphology of the powder and caused amorphization and partial changes in the structure of the crystalline phase. Monolithic samples were obtained from the pretreated polymer with a hot‐pressing method in a wide range of temperatures. The effect of preliminary deformation processing on the mechanical properties of UHMWPE was studied. It was revealed that during monolitization in its melting temperature range, the mechanical properties of the powder increased, whereas the percentage elongation decreased. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 2971–2977, 2013     

Effect of thermal treatment on the tensile and in‐plane shear behavior of carbon fiber‐reinforced poly(phenylene sulfide) composite specimens

The effect of PPS matrix evolution occurring during thermal treatment of carbon fiber‐reinforced PPS plies prior to their consolidation to laminates on the mechanical behavior of the composite material has been investigated. The thermal treatments were performed at temperatures and times, which are relevant for processing PPS composites. All thermal treatments were carried out in an oven in air to facilitate the presence of oxygen, while the subsequent consolidation was performed in an autoclave. The tensile and in‐plane shear behavior of both, thermal‐treated and untreated materials, was investigated. Differential scanning calorimetry and microscopy analyses were made to evaluate the effect of the performed thermal treatments on degree of crystallinity and porosity of the laminates. The mechanical tests carried out have shown an appreciable degradation of the mechanical properties investigated. The observed degradation increases with increasing thermal treatment temperature and time when thermal treatments were carried out on each single composite ply prior to the consolidation. On the other hand, when, prior to the consolidation, the whole set of plies was subjected to thermal treatment, improved mechanical properties were observed. The results were discussed under the viewpoint of PPS matrix evolution during processing of the composite plies in the presence of oxygen. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Two‐stage drawing process to prepare high‐strength and porous ultrahigh‐molecular‐weight polyethylene fibers: Cold drawing and hot drawing

High‐strength and porous ultrahigh‐molecular‐weight polyethylene (UHMWPE) fibers have been prepared through a two‐stage drawing process. Combined with tensile testing, scanning electron microscopy, and small‐angle X‐ray scattering, the mechanical properties, porosity, and microstructural evolution of the UHMWPE fibers were investigated. The first‐stage cold drawing of the gel‐spun fibers and subsequent extraction process produced fibers with oriented lamellae stacks on the surface and plentiful voids inside but with poor mechanical properties. The second‐stage hot drawing of the extracted fibers significantly improved the mechanical properties of the porous fibers because of the formation of lamellar backbone networks on the surface and microfibrillar networks interwoven inside to support the voids. With various processing conditions, the optimized mechanical properties and porosity of the prepared UHMWPE fibers were obtained a tensile strength of 1.31 GPa, a modulus of 10.1 GPa, and a porosity of 35%. In addition, a molecular schematic diagram is proposed to describe structural development under two‐stage drawing, including void formation and lamellar evolution. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42823.     

Injection and injection compression molding of ultra‐high‐molecular weight polyethylene powder

Ultra‐high‐molecular weight polyethylene (UHMWPE) powder was processed using injection molding (IM) with different cavity thicknesses and injection‐compression molding (ICM). The processing parameters of feeding the powders were optimized to ensure proper dosage and avoid jeopardizing the UHMWPE molecular structure. Dynamic mechanical analysis (DMA) and Fourier‐transform infrared spectroscopy tests confirmed that the thermal and oxidative degradations of the material were avoided but crosslinking was induced during melt processing. Tensile tests and impact tests showed that the ICM samples were superior to those of IM. Increased cavity thickness and ICM were helpful for reducing the injection pressure and improving the mechanical properties due to effective packing of the material. Short shot molding showed that the UHMWPE melt did not exhibit the typical progressive and smooth melt front advancements. Due to its highly entangled polymer chains structure, it entered the cavity as an irregular porous‐like structure, as shown by short shots and micro‐computed tomography scans. A delamination skin layer (around 300‐μm thick and independent of cavity thickness) was formed on all IM sample surfaces while it was absent in the ICM samples, suggesting two different flow behaviors between IM and ICM during the packing phase. POLYM. ENG. SCI., 59:E170–E179, 2019. © 2018 Society of Plastics Engineers     

Effect of the ultradrawing behavior of gel films of ultrahigh‐molecular‐weight polyethylene and low‐molecular‐weight polyethylene blends on their physical properties

This study examined the effect of the ultradrawing behavior of gel film specimens of ultrahigh‐molecular‐weight polyethylene (UHMWPE) and UHMWPE/low‐molecular‐weight polyethylene (LMWPE) blends on their physical properties. The concentration of a gel film approximated its critical concentration at a fixed drawing temperature; its achievable draw ratio was higher than that of other blend specimens with various concentrations. Noticeably, when about 5 wt % LMWPE was added to a UHMWPE/LMWPE gel film specimen, the achievable draw ratio of the gel film increased, and this contributed to an apparent promoting effect on its anticreeping properties and thermal stability. Therefore, when UL_B?0.9 was drawn to a draw ratio of 300, the anticreeping behavior was improved to less than 0.026%/day. Moreover, with respect to the thermal stability, when the same specimen was drawn to a draw ratio of 300, the retention capability of its storage modulus could resist a high temperature of 150°C, which was obviously much higher than the temperature of an undrawn gel film specimen (70°C). To study these interesting behaviors further, this study systematically investigated the gel solution viscosities, anticreeping properties, dynamic mechanical properties, thermal properties, molecular orientations, and mechanical properties of undrawn and drawn UHMWPE/LMWPE gel film specimens. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2008     

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

Polydopamine (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     

High‐density polyethylene/ultrahigh‐molecular‐weight polyethylene blend. I. The processing,thermal, and mechanical properties

Various blend ratios of high‐density polyethylene (HDPE) and ultrahigh‐molecular‐weight polyethylene (UHMWPE) were prepared with the objective of determining their suitability as biomaterials. Although the presence of HDPE in the blends enabled melt processing, the presence of UHMWPE helped to improve the toughness of the resulting blends. The processability of the blends was investigated with the Brabender torque, which was used as an indication of the optimum blend conditions. The blends were characterized with differential scanning calorimetry. The mechanical tests performed on the blends included tensile, flexural, and impact tests. A 50:50 (w/w) blend yielded optimum properties in terms of the processability and mechanical properties. The tensile property of the 50:50 blend was intermediate between those of HDPE and UHMWPE, but the strain at break increased 200% in comparison with that of both neat resins. The energy at break of the 50:50 blend revealed an improvement in the toughness. The fracture mechanism was also investigated with scanning electron microscopy. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 413–425, 2005     

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

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

Development of porous UHMWPE morphologies for fixation of gel‐based materials

Novel gel‐based materials including hydrogels and bioderived polymers show great potential in orthopedics but require a means of mechanical fixation to a substrate. The development of controlled porous ultra‐high‐molecular‐weight polyethylene (UHMWPE) morphologies is targeted to expand the future potential for UHMWPE‐based composites with such novel bioderived materials. Porous UHMWPE morphologies were produced by means of a sodium chloride leaching process. Compression‐molded samples were prepared by dry mixing of sized NaCl particles and UHMWPE powder. These were then soaked in water to remove the porogen, leaving a porous UHMWPE structure. The mass of removed porogen and resulting void density were found to match well with Monte Carlo simulations. Distribution of NaCl particles was greatly influenced by the ratio of particle sizes between NaCl and UHMWPE. Limited percolation was achievable at NaCl concentrations below 50 wt %, whereas porogen concentrations above 60 wt % led to interconnected networks. Porous UHMWPE scaffolds were impregnated with gelatin to explore the penetration of a gel‐based phase. It was observed that the gelatin was able to permeate the UHMWPE to a great extent, except for unfilled voids due either to entrapped air or insufficient channel diameters to accommodate gelatin flow. These results confirm that porous morphologies can be created in a controlled manner and tailored for chosen applications. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Rheological,thermal, and morphological properties of low‐density polyethylene/ultra‐high‐molecular‐weight polyethylene and linear low‐density polyethylene/ultra‐high‐molecular‐weight polyethylene blends

The dynamic rheological behavior of low‐density polyethylene (LDPE)/ultra‐high‐molecular‐weight polyethylene (UHMWPE) blends and linear low‐density polyethylene (LLDPE)/UHMWPE blends was measured in a parallel‐plate rheometer at 180, 190, and 200°C. Analysis of the log–additivity rule, Cole–Cole plots, Han curves, and Van Gurp curves of the LDPE/UHMWPE blends indicated that the blends were miscible in the melt. In contrast, the rheological properties of LLDPE/UHMWPE showed that the miscibility of the blends was decided by the composition of LLDPE. The differential scanning calorimetry results and scanning electron microscopy photos of the LLDPE/UHMWPE blends were consistent with the rheological properties, whereas with regard to the thermal and morphological properties of LDPE/UHMWPE blends, the results reveal three endothermic peaks and phase separation, which indicated a liquid–solid phase separation in the LDPE/UHMWPE blends. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Solid‐state compaction and drawing of nascent reactor powders of ultra‐high‐molecular‐weight polyethylene

The continuous production of ultra‐high‐molecular‐weight polyethylene (UHMWPE) filaments was studied by the direct roll forming of nascent reactor powders followed by subsequent multistage orientation drawing below their melting points. The UHMWPE reactor powders used in this study were prepared by the polymerization of ethylene in the presence of soluble magnesium complexes, and they exhibited high yield even at low reaction temperatures. The unique, microporous powder morphology contributed to the successful compaction of the UHMWPE powders into coherent tapes below their melting temperatures. The small‐angle X‐ray scattering study of the compacted tapes revealed that folded‐chain crystals with a relatively long‐range order were formed during the compaction and were transformed into extended‐chain crystals as the draw ratio increased. Our results also reveal that the drawability and tensile and thermal properties of the filaments depended sensitively on both the polymerization and solid‐state processing conditions. The fiber drawn to a total draw ratio of 90 in the study had a tensile strength of 2.5 GPa and a tensile modulus of 130 GPa. Finally, the solid‐state drawn UHMWPE filaments were treated with O₂ plasma, and the enhancement of the interfacial shear strength by the surface treatment is presented. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 718–730, 2005     

Thermal and dynamic mechanical properties of vitamin E infused and blended ultra‐high molecular weight polyethylenes

Vitamin E (or α‐tocopherol) is an alternative via to thermal treatments to achieve oxidative stability of gamma or electron beam irradiated ultra‐high molecular weight polyethylenes (UHMWPE) used in total joint replacements. Our aim was to study the effects of vitamin E on the molecular dynamics and microstructural properties of UHMWPE. We hypothesized that the antioxidant would plasticize UHMWPE. Vitamin E was incorporated into UHMWPE at different concentrations by diffusion and blending and detected by ultraviolet and infrared spectroscopies from 500 ppm and 4000 ppm, respectively. Dynamic mechanical thermal analysis was used to characterize the influence of this antioxidant in the relaxations of the raw material. Differential scanning calorimetry and transmission electron microscopy served to characterize thermal and microstructure properties, respectively. Vitamin E concentrations above 3% by weight significantly reduced the degree of crystallinity and increased the melting transition temperature of raw UHMWPE. The presence of increasing concentrations of α‐tocopherol introduced and/or strengthened the beta relaxation, which was also shifted toward gradually lower temperatures and had rising activation energies up to 188 kJ/mol. In addition, the gamma relaxation remained unaltered on vitamin E addition. Therefore, no plasticizing effects of vitamin E on the molecular dynamics of UHMWPE could be confirmed from mechanical spectroscopy data. However, the α relaxation was modified in intensity and location due to the changes in the degree of crystallinity introduced by the incorporation of vitamin E. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

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.     

Photocrosslinking of halogen‐free flame‐retarded ethylene‐vinyl acetate copolymer by phosphorous‐nitrogen compound NP28

The photoinitiated crosslinking of halogen‐free flame‐retarded ethylene‐vinyl acetate copolymer (EVA) by the phosphorous‐nitrogen compound NP28 in the presence of photoinitiator and crosslinker and characterization of the related properties have been investigated by gel determination, heat extension test, thermogravimetric analysis (TGA), mechanical measurement, and thermal aging test. The photocrosslinking efficiency of EVA/NP28 blend and various factors affecting the crosslinking process, such as photoinitiator, crosslinker, NP28 content, and irradiation temperature, were studied in detail and optimized by comparison of gel content. The results show that the EVA/NP28 blend filled with 28.2 wt % NP28 with a thickness of 1.6 mm is homogeneously photocrosslinked to a gel content of above 80 wt % with 4.8 s UV‐irradiation under optimum conditions. The data from TGA, mechanical measurement, and thermal aging test give evidence that the thermal stability and mechanical properties of photocrosslinked EVA/NP28 blend are much better than those of the unphotocrosslinked one.© 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

The effects of hybrid fillers on thermal,mechanical, physical,and antimicrobial properties of ultrahigh‐molecular‐weight polyethylene‐reinforced composites

The effects of hybrid filler of zinc oxide and chitosan (chitosan–ZnO) on thermal, flexural, antimicrobial, chemical resistance, and hardness properties of ultrahigh‐molecular‐weight polyethylene (UHMWPE) composites with varying concentration of zinc oxide (ZnO) and further hybridized by chitosan (CS) were successfully studied. The composites were prepared using mechanical ball milling and followed by hot compression molding. The addition of ZnO to the UHMWPE matrix had lowered the melting temperature (T _m) of the composite but delayed its degradation temperature. Further investigation of dual filler incorporation was done by the addition of chitosan to the UHMWPE/ZnO composite and resulted in the reduction of UHMWPE crystallization. The flexural strength and modulus had a notably high improvement through ZnO addition up to 25 wt% as compared to neat UHMWPE. However, the addition of chitosan had resulted in lower flexural strength than that of 12 wt% ZnO UHMWPE composite but still higher than that of neat UHMWPE. It was experimentally proven that the incorporation of ZnO and chitosan particles within UHMWPE matrix had further enhanced the antimicrobial properties of neat UHMWPE. Chemical resistance was improved with higher ZnO content with a slight reduction of mass change after the incorporation of chitosan. The hardness value increased with ZnO addition but higher incorporation of chitosan had lowered the hardness value. These findings have significant implications for the commercial application of UHMWPE based products. It appears that these hybrid fillers (chitosan–ZnO)‐reinforced UHMWPE composites exhibit superior overall properties than that of conventional neat UHMWPE. POLYM. COMPOS., 38:1689–1697, 2017. © 2015 Society of Plastics Engineers     

Thermal stability and chemical durability of PVC‐based biomedical devices

Poly(vinyl chloride) (PVC)‐based blood circuits for extracorporeal hemodialysis were investigated for the assessment of their thermal stability as well as their chemical durability towards ionizing radiation sterilization and environmental conditions of storage and transportation. Thermal degradation was monitored by measuring the amount of hydrochloric acid (HCl) evolved as a function of different thermal stresses. HCl was extracted from the internal lumen of the blood circuits, and then quantitatively evaluated under the corresponding form of chloride ions by chromatographic technique (HPLC‐IC). Behavior of PVC heat stabilizers was evaluated as well, determining also the concentration of calcium and zinc released by the investigated materials, by flame atomic absorption spectroscopy (FAAS) technique. Electron beam irradiation revealed an impact on blood tubing higher than that of environmental storage conditions. Nevertheless, real operative cases of sterilization and storage conditions turned out to be quite safe, and all blood circuits displayed good performances in terms of thermal stability. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102:5378–5387, 2006     

Ultradrawing properties of ultrahigh‐ molecular‐weight polyethylene/carbon nanotube fibers prepared at various formation temperatures

The influence of formation temperature on the ultradrawing properties of ultrahigh‐molecular‐weight polyethylene/carbon nanotube (UHMWPE/CNT) fiber specimens is investigated. Gel solutions of UHMWPE/CNT with various CNT contents were gel‐spun at the optimum concentration and temperature but were cooled at varying formation temperatures in order to improve the ultradrawing and tensile properties of the UHMWPE/CNT composite fibers. The achievable draw ratio (D_ra) values of UHMWPE/CNT as‐prepared fibers reach a maximum when they are prepared with the optimum CNT content and formation temperature. The D_ra value of UHMWPE/CNT as‐prepared fibers produced using the optimum CNT content and formation temperature is about 33% higher than that of UHMWPE as‐prepared fibers produced using the optimum concentration and formation temperature. The percentage crystallinity (W_c) and melting temperature (T_m) of UHMWPE/CNT as‐prepared fiber specimens increase significantly as the formation temperature increases. In contrast, W_c increases but T_m decreases significantly as the CNT content increases. Dynamic mechanical analysis of UHMWPE and UHMWPE/CNT fiber specimens exhibits particularly high α‐transition and low β‐transition, wherein the peak temperatures of α‐transition and β‐transition increase dramatically as the formation temperature increases and/or CNT content decreases. In order to understand these interesting drawing, thermal and dynamic mechanical properties of the UHMWPE and UHMWPE/CNT as‐prepared fiber specimens, birefringence, morphological and tensile studies of as‐prepared and drawn fibers were carried out. Possible mechanisms accounting for these interesting properties are proposed. Copyright © 2010 Society of Chemical Industry