Surface modification of ultra‐high‐molecular‐weight polyethylene. I. Characterization and sintering studies

We performed surface modification of ultra‐high‐molecular‐weight polyethylene (UHMWPE) through chromic acid etching with the aim of improving the performance of UHMWPE's composites with poly(ethylene terephthalate) fibers. In part I of this study, we evaluated the effects of chemical modification on the surface properties of UHMWPE with X‐ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), and contact angle measurements. The thermal properties, rheology, and sintering behavior of the modified UHMWPE were compared to those of the base material. XPS and FTIR analysis confirmed the presence of carboxyl and hydroxyl groups on the surface of the modified powders. The substitution of polar groups into the backbone of the polymer decreased its contact angles with water and hexadecane and increased its surface energy, as evidenced by contact angle measurements. The modified UHMWPE was more crystalline than the base resin and less prone to thermal degradation. Although the rheological properties were virtually identical, the modified powders sintered more readily, presumably due to their higher surface energy, which suggested enhanced processability by compression molding. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci, 2006     

Improvement of the tribological behavior of ultra‐high‐molecular‐weight polyethylene by incorporation of poly (phenyl p‐hydroxyzoate)

Ultra‐high‐molecular‐weight polyethylene/poly (phenyl p‐hydroxyzoate) composites (coded as UHMWPE/PPHZ) were prepared by compression molding. The effects of the poly (phenyl p‐hydroxyzoate) on the tribological properties of the UHMWPE/PPHZ composites were investigated, based on the evaluations of the tribological properties of the composites with various compositions and the examinations of the worn steel surfaces and composites structures by means of scanning electron microscopy and transmission electron microscopy. It was found that the incorporation of the PPHZ led to a significant decrease in the wear rate of the composites. The composites with the volume fraction of the PPHZ particulates within 45% ～ 75% showed the best wear resistance. The friction coefficient of the UHMWPE/PPHZ composites decreased with increasing load and sliding velocity, while the wear rates increased with increasing load. This was attributed to the enhanced softening and plastic deformation of the composites at elevated load or sliding velocity. The UHMWPE/PPHZ composites of different compositions had differences in the microstructures and the transfer film characteristics on the counterpart steel surface as well. This accounted for their different friction and wear behaviors. The transfer film of the UHMWPE/PPHZ composites appeared to be thinner and more coherent, which was largely responsible for their better wear resistance of t composite than the UHMWPE matrix. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 2336–2343, 2005     

Mechanical properties of surface‐modified ultra‐high molecular weight polyethylene fiber reinforced natural rubber composites

The mechanical properties of ultra‐high molecular weight polyethylene (UHMWPE) fibers reinforced natural rubber (NR) composites were determined, and the effects of fiber surface treatment and fiber mass fraction on the mechanical properties of the composites were investigated. Chromic acid was used to modify the UHMWPE fibers, and the results showed that the surface roughness and the oxygen‐containing groups on the surface of the fibers could be effectively increased. The NR matrix composites were prepared with as‐received and chromic acid treated UHMWPE fibers added 0–6 wt%. The treated UHMWPE fibers increased the elongation at break, tear strength, and hardness of the NR composites, especially the tensile stress at a given elongation, but reduced the tensile strength. The elongation at break increased markedly with increasing fiber mass fraction, attained maximum values at 3.0 wt%, and then decreased. The tear strength and hardness exhibited continuous increase with increasing the fiber content. Several microfibrillations between the fiber and NR matrix were observed from SEM images of the fractured surfaces of the treated UHMWPE fibers/NR composites, which meant that the interfacial adhesion strength was improved. POLYM. COMPOS., 38:1215–1220, 2017. © 2015 Society of Plastics Engineers     

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     

Injection molding of delamination‐free ultra‐high‐molecular‐weight polyethylene

When ultra‐high‐molecular‐weight polyethylene (UHMWPE) in powder form is injection molded, the so‐called delamination layering occurs near the skin of the parts. This layering defect hampers UHMWPE's superior wear resistance property and part surface quality. The delamination layer was caused by a combination of excessive shear stress near the part surface and high degree of molecular entanglement of UHMWPE. A mold insulation method that delays the rapid cooling of UHMWPE to reduce the shear stress and improve the polymer chain “interdiffusion” across the entangled chain bundles was used to eliminate the delamination layer. When the insulation layer thickness and mold temperature were optimized, the delamination layer was eliminated completely while still maintaining a reasonable cooling/cycle time. The delamination‐free parts were found to regain UHMWPE's superior impact resistance and tensile properties. POLYM. ENG. SCI., 59:2313–2322, 2019. © 2019 Society of Plastics Engineers     

Thermal properties,rheology and sintering of ultra high molecular weight polyethylene and its composites with polyethylene terephthalate

The addition of polyethylene terephthalate (PET) fibers in ultra high molecular weight polyethylene (UHMWPE) may be a promising approach to achieve improved wear properties in artificial joints. Since UHMWPE/PET composites are processed by compression molding, which involves compaction and sintering of polymeric powders, this article investigates their rheology, thermal properties, and sintering behavior to aid in the identification and selection of optimum processing conditions. Isothermal crystallization kinetics studies have revealed that crystallization of UHMWPE proceeds via heterogeneous nucleation and is governed by two‐dimensional growth. The crystallization rates of the composites were lower than those of the neat material, whereas their ultimate crystallinities were higher. The UHMWPE/PET composites had higher viscosity and elasticity than the neat resin. In the presence of PET fibers the onset of sintering took place at higher temperatures but proceeded at substantially higher rates as compared with pure UHMWPE. A marked discrepancy between the Eshelby‐Frenkel model and experimental sintering data suggests that viscous flow is not the prevailing mechanism for coalescence but rather that enhanced surface area, attributed to the highly developed internal morphology of UHMWPE particles, is the controlling factor. POLYM. ENG. SCI., 45:678–686, 2005. © 2005 Society of Plastics Engineers     

Surface modification of ultra‐high molecular weight polyethylene fiber by different kinds of SiO2 nanoparticles

We successfully improved the interfacial adhesion strength between ultra‐high molecular weight polyethylene (UHMWPE) fiber and resin by the surface modification of UHMWPE fiber with two kinds of SiO₂ nanoparticles through gel spinning process. Modified effect of treated SiO₂ nanoparticles by coupling agent was superior to original SiO₂ nanoparticles. Compared with unmodified fibers, pull‐out tests of modified UHMWPE/treated SiO₂ fibers revealed that interfacial adhesion strength increased by the maximum of 10.95%, but corresponding breaking strength decreased by 8.51%. In addition, the interfacial adhesion strength and breaking strength could continue to enhance with increasing the additive amount of treated SiO₂ nanoparticles. The results of Differential Scanning Calorimetry (DSC), X‐ray diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), and Scanning Electron Microscopy (SEM) indicated that the crystallinity of all modified fibers decreased while crystallite dimension increased, and the surface of modified fibers by treated SiO₂ nanoparticles exhibited polar functional group (C=O). The superiority of this modified technology was that it realized the bulk industrial production and maneuverability, low cost, and no pollution. POLYM. COMPOS., 38:1928–1936, 2017. © 2015 Society of Plastics Engineers     

Friction and wear properties of graphene oxide/ultrahigh‐molecular‐weight polyethylene composites under the lubrication of deionized water and normal saline solution

Ultrahigh‐molecular‐weight polyethylene (UHMWPE) and UHMWPE composites reinforced with graphene oxide (GO) were successfully fabricated through a new step of liquid‐phase ultrasonic dispersion, high‐speed ball‐mill mixing, and hot‐pressing molding technology. When the GO/UHMWPE composites were lubricated with deionized water (DW) and normal saline (NS) solution, their friction and wear properties were investigated through sliding against ZrO₂. The worn surface and wear volume losses of these composites were studied with scanning electron microscopy, X‐ray photoelectron spectroscopy, and a Micro‐XAM 3D non‐contact surface profiler. The results show that the microhardness of the GO/UHMWPE composites was improved by 13.80% and the wear rates were decreased by 19.86 and 21.13%, whereas the depths of the scratches were decreased by 22.93 and 23.77% in DW and NS lubricating conditions, respectively. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39640.     

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.     

Surface modification and physical properties of various UHMWPE‐fiber‐reinforced modified epoxy composites

Two surface modification methods—plasma surface treatment and chemical agent treatment—were used to investigate their effects on the surface properties of ultrahigh‐molecular‐weight polyethylene (UHMWPE) fibers. In the analyses, performed using electron spectroscopy for chemical analysis, changes in weight, and scanning electron microscope observations, demonstrated that the two fiber‐surface‐modified composites formed between UHMWPE fiber and epoxy matrix exhibited improved interfacial adhesion and slight improvements in tensile strengths, but notable decreases in elongation, relative to those properties of the composites reinforced with the untreated UHMWPE fibers. In addition, three kinds of epoxy resins—neat DGEBA, polyurethane‐crosslinked DGEBA, and BHHBP‐DGEBA—were used as resin matrices to examine the tensile and elongation properties of their UHMWPE fiber‐reinforced composites. From stress/strain measurements and scanning electron microscope observations, the resin matrix improved the tensile strength apparently, but did not affect the elongation. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 655–665, 2007     

Effect of polyethylene‐graft‐maleic anhydride as a compatibilizer on the mechanical and tribological behaviors of ultrahigh‐molecular‐weight polyethylene/copper composites

Ultrahigh‐molecular‐weight polyethylene/copper (UHMWPE/Cu) composites compatibilized with polyethylene‐graft‐maleic anhydride (PE‐g‐MAH) were prepared by compression molding. The effects of the compatibilizer on the mechanical, thermal, and tribological properties of the UHMWPE/Cu composites were investigated. These properties of the composites were evaluated at various compositions, and worn steel surfaces and composite surfaces were examined with scanning electron microscopy and X‐ray photoelectron spectroscopy. The incorporation of PE‐g‐MAH reduced the melting points of the composites and increased their crystallinity to some extent. Moreover, the inclusion of the PE‐g‐MAH compatibilizer greatly increased the tensile rupture strength and tensile modulus of the composites, and this improved the wear resistance of the composites. These improvements in the mechanical and tribological behavior of the ultrahigh‐molecular‐weight‐polyethylene‐matrix composites with the PE‐g‐MAH compatibilizer could be closely related to the enhanced crosslinking function of the composites in the presence of the compatibilizer. Moreover, the compatibilizer had an effect on the transfer and oxidation behavior of the filler Cu particulates, which could be critical to the application of metallic‐particulate‐filled polymer composites in engineering. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 948–955, 2004     

Control of the interfacial properties of ultrahigh‐molecular‐weight polyethylene/magnesium hybrid composites through use of atmospheric plasma treatment

This work aims to explore the use of lightweight magnesium alloys as an advanced composite material in conjunction with lightweight thermoplastic materials, such as ultrahigh‐molecular‐weight polyethylene (UHMWPE). High throughput, environmentally friendly, atmospheric plasma treatment methods were used to control the interfacial properties and improve the adhesion behavior of metallic/UHMWPE composites. Helium‐oxygen dielectric barrier discharges were used, and the plasma‐activated UHMWPE surfaces were characterized through analytical and mechanical characterization methods. Oxygen content on the treated polymer surfaces increased 18.1–36.0%. A reduction in silicon content combined with characterization through microscopy reveal a preference for the attack of the matrix over the polyethylene fibers. Wetting angles for the treated samples decreased as much as 53.7%. Treated UHMWPE/Mg hybrid samples exhibited lap shear strengths up to 113.7% greater than the control. Both the plasma‐induced surface functionalization with oxygen‐containing polar groups (carboxyl, carbonyl, and hydroxyl groups) and the preferential mild etching of the polymer matrix over the fibers lead to the improvement in adhesion. POLYM. COMPOS., 2012. © 2011 Society of Plastics Engineers     

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.     

Modeling the oxidative degradation of ultra‐high‐molecular‐weight polyethylene

Understanding the sequence of reactions that occur in ultra‐high‐molecular‐weight polyethylene (UHMWPE) following ⁶⁰Co γ irradiation has been the focus of numerous experimental studies. In the study reported here, we have incorporated recent experimental findings into a mathematical model for UHMWPE oxidation. Simulation results for shelf aging and accelerated aging are presented. It is shown that very reasonable simulations of shelf‐aging and accelerated‐aging data can be obtained. It is also shown that simulations of shelf aging in reduced oxygen environments predict that the subsurface peaks of ketones will be shifted to the exterior surface. In vivo aging can be simulated if we assume that the oxygen level in the synovial fluid is about one‐eighth that of atmospheric levels. Some reduced irradiation doses are predicted to significantly reduce the ketone formation for shelf‐aging periods of up to 10 years. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 814–826, 2003     

Preparation and characterization of cerium‐doped titanium dioxide/ultrahigh‐molecular‐weight polyethylene porous composites with excellent photocatalytic activity

Porous ultrahigh‐molecular‐weight polyethylene (UHMWPE)‐based composites filled with surface‐modified Ce‐doped TiO₂ nanoparticles (Ce–TiO₂/UHMWPE) were prepared by template dissolution. The composites were characterized by Fourier transform infrared spectroscopy, ultraviolet (UV)–visible spectroscopy, diffuse reflectance spectra, and scanning electron microscopy); the photocatalytic activity was also evaluated by the decomposition of methyl orange under UV exposure. The results demonstrate that the severe aggregation of Ce–TiO₂ nanoparticles could be reduced by surface modification via a silane coupling agent (KH570). The Ce–TiO₂/UHMWPE porous composites exhibited a uniform pore size. Doping with Ce⁴⁺ effectively extended the spectral response from the UV to the visible region and enhanced the surface hydroxyl groups of the TiO₂ attached to the matrix. With a degradation rate of 85.3%, the 1.5 vol % Ce–TiO₂/UHMWPE sample showed the best photocatalytic activity. The excellent permeability of the porous composites is encouraging for their possible use in wastewater treatment. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Size effect of charcoal particles on the properties of bamboo charcoal/ultra‐high molecular weight polyethylene composites

This study was aimed at examining the size effect of charcoal particles on the properties of bamboo charcoal (BC)/ultra‐high molecular weight polyethylene (UHMWPE) composites. Four types of BC with various particle sizes were mixed with UHMWPE using a twin‐screw extruder. It was found that the melting temperature and crystallinity of the composites were slightly decreased with the addition of BC. The incorporation of BC remarkably improved the tensile properties and creep resistance of UHMWPE, and the particle size of BC strongly affected the properties of BC/UHMWPE composites. The BC with lowest particle size exhibited best reinforcement, where the tensile strength and Young's modulus were increased by 385% and 517% compared with neat UHMWPE. The composites with 70 wt % BC possessed conductivities of 16.8, 14.1, 13.5, and 10.9 S/m. The storage modulus and glass transition temperature of the composites also increased with the addition of BC. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45530.     

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     

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     

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     

Influence of different sterilization procedures on the morphological parameters and mechanical properties of ultra‐high‐molecular‐weight polyethylene

The objectives of this study were to examine the effects of the processing conditions, sterilization, and thermal treatment on the morphological and mechanical properties of ultra‐high‐molecular‐weight polyethylene (UHMWPE) in medical applications by means of thermal analysis, Fourier transform infrared spectroscopy, and nanoindentation. It is well known that manufacturing, irradiation, and thermal treatments significantly alter the microstructure of materials, which results in changes in their mechanical properties. UHMWPE was found to be barely sensitive to processing conditions but strongly influenced by sterilization treatments. Great emphasis was given to the characterization of the so‐called first generation of highly crosslinked UHMWPE because the thermal history of this material differed from that of γ‐irradiated materials. The physical and mechanical properties of UHMWPE were influenced as a result of γ and electron‐beam irradiation and the remelting procedure. Lower crystallinity, different lamellar thickness distributions, and lower hardness and modulus values were estimated. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011