Molecular orientation evolution during low‐density polyethylene blown film extrusion using real‐time Raman spectroscopy

Real‐time polarized Raman spectroscopy was used in this study to measure the molecular orientation evolution during blown film extrusion of low‐density polyethylene (LDPE). Spectra were obtained at different locations along the blown film line, starting from the molten state near the die and extending up to the solidified state near the nip rolls. The trans C C symmetrical stretching vibration of polyethylene (PE) at 1132 cm⁻¹ was analyzed for films possessing uniaxial symmetry. For the given peak, the principal axis of the Raman tensor is coincident with the c‐axis of the orthorhombic crystal, and was used to solve a set of intensity ratio equations to obtain second (〈P₂(cosθ)〉) and fourth (〈P₄(cosθ)〉) moments of the orientation distribution function. The orientation parameters (P₂, P₄) were found to increase along the axial distance in the film line even past the frost‐line height (FLH). The P₂ values also showed an increasing trend with crystalline evolution during extrusion, consistent with past observations that molecular orientation takes place even after the blown film diameter is locked into place. It was also found that the integral ratio (I₁₁₃₂/I₁₀₆₄) obtained from a single, ZZ‐back‐scattered mode can provide a reasonable estimate of molecular orientation. These results indicate the potential of real‐time Raman spectroscopy as a rapid microstructure monitoring tool for better process control during blown film extrusion. Copyright © 2008 John Wiley & Sons, Ltd.     

Raman polarization analysis of highly crystalline polyethylene fiber

The complex orientation dependence in space of Raman active vibrations in the orthorhombic structure of polyethylene (PE) is discussed in terms of Raman tensor elements as intrinsic physical parameters of the lattice. Building upon the symmetry assignment of these vibrational modes, we systematically studied, from both theoretical and experimental viewpoints, the changes of polarized intensity for the A_g and the B_2g + B_3g vibrational modes with respect to PE molecular orientation. After explicitly expanding the Raman selection rules associated with the A_g and the B_2g + B_3g modes, introducing them into general expressions of the orientation distribution function, and validating them by means of a least‐square fitting procedure on experimental data, we compare here two mesostructural models for a highly crystallized and self‐aligned PE fiber structure. Stereological arguments are shown concerning the arrangement of orthorhombic fibrils in such a sample that unfold the correct values of five independent Raman tensor elements for orthorhombic PE. Copyright © 2010 John Wiley & Sons, Ltd.     

Study on the Structure and Properties of UHMWPE/Epoxy Resin Composite Fiber

The preparation, crystallization behavior, and fiber structure and properties of ultrahigh molecular weight polyethylene (UHMWPE) epoxy resin composite fiber were studied by means of differential scanning calorimeter (DSC), X‐ray diffraction (XRD), Scanning electron microscopy (SEM), thermogravimetric analysis (TGA), and tensile testing. The morphology showed a different behavior from pure polyethylene (PE) fiber. The fiber mechanical properties, creep behavior, and thermal properties of UHMWPE fiber can be improved by adding epoxy resin. It's believed that the epoxy can serve as a physical cross‐linking agent to limit the motion or migration of PE molecules and consequently improve the fiber creep property. However, when the content of epoxy resin is higher than 5 wt%, all of the behavior and properties deteriorate.     

The effects of contact area and applied load on the morphology of in vitro worn ultra‐high molecular weight knee prostheses: a micro‐Raman and gravimetric study

Ultra‐high molecular weight polyethylene knee prostheses of two different sizes (i.e. characterised by different contact areas) were run on a knee wear simulator in two tests differing for the applied load. Gravimetric and micro‐Raman spectroscopic analyses were performed to investigate at macroscopic and molecular levels the effects of contact area and applied load on the morphology of the knee components. The larger prostheses showed a higher mass loss in both tests, while Raman spectroscopy showed a more significant polymer degradation in the smaller prostheses, suggesting that a lower contact area is responsible for a higher wear at the molecular wear, but for a lower gravimetric wear. Raman measurements showed that in the second test (using a higher applied load), the wear mechanism changed with respect to the first test: the less severe conditions used in the latter resulted in an increase in the orthorhombic content, while the more severe conditions used in the former determined an increase and rearrangement of the amorphous phase. The results here reported allow to gain more insights into the effects of contact area, applied load and contact stress on wear. Preliminary micro‐Raman analyses on in vivo worn knee prostheses confirmed the results obtained in vitro: the retrievals of smaller size were found more degraded at molecular level than those of larger size. These findings showed that the conditions used in the in vitro tests well simulate the knee kinematics of the knee joint and thus the in vivo wear. Copyright © 2014 John Wiley & Sons, Ltd.     

Tribological characterisation of Zr-based bulk metallic glass in simulated physiological media

Due to their excellent wear resistant properties and high strength, as well as a low Young's modulus, Zr-based bulk metallic glasses (BMGs) are potentially suitable biomaterials for low-friction arthroplasty. The wear characteristics of the Zr_60.14Cu_22.31Fe_4.85Al_9.7Ag₃ bulk amorphous alloy against ultra-high-molecular-weight polyethylene (UHMWPE) compared to a CoCrMo/UHMWPE combination were investigated in two different wear screening test devices, reciprocating and unidirectional. Hank's solution and sterile calf bovine serum were selected as the lubricant fluid media. It was found that different fluid media had insignificant effect on polyethylene wear against BMG counterfaces. The wear behaviour obtained on both test devices demonstrated that Zr-based BMG achieved UHMWPE counterface wear rates superior to conventional cast CoCrMo alloy, where the wear rate of UHMWPE is decreased by over 20 times. The tribological performance of these joints is superior to that of conventional metal-on-polymer designs. Contact angle measurements suggested that the advantage of BMG over a CoCrMo alloy counterface is attributed to its highly hydrophilic surfaces.     

Mechanical,Thermal, and Surface Properties of Ultrahigh Molecular Weight Polyethylene/Polypropylene Blends

Various compositions of ultrahigh molecular weight polyethylene/polypropylene (UHMWPE/PP) blends were prepared in decalin, with the rheological, mechanical, thermal, and surface properties of the blends being determined using the solution cast film. Viscosity and mechanical properties of the blends decreased below the additivity value with increasing PP content implying that PP molecules disturb the entanglement of UHMWPE. Contact angle of the blend films with a water drop increased with increasing content of PP. The atomic force microscope (AFM) images showed that the surface of cast UHMWPE was very smooth whereas that of cast PP was very uneven. For blends, the surface became rough and uneven with increasing content of PP. The melting temperature of PP (T _mP) decreased in the blends with increasing UHMWPE content while that of UHMWPE (T _mU) remained almost constant in blends.     

New and Simple Staining Method for Visualizing UHMWPE Lamellar Structure in TEM

Ultra-high-molecular-weight polyethylene (UHMWPE) is used in arthroplasty as a key component of total joint replacements. In order to increase its wear resistance, the polymer is often cross-linked in a two-step procedure comprising irradiation and thermal treatment. Both modification steps impact UHMWPE lamellar structure. In this study we introduce a new staining method that makes it possible to visualize the UHMWPE lamellae by transmission electron microscopy (TEM). The method consists of one-step staining with oleum (H ₂ SO ₄ solution of SO ₃ ) for 4 days and ultramicrotomy; this is significantly simpler than previously described techniques and yields micrographs of the same quality. The lamellar thicknesses from TEM correlated well with those from small- and wide-angle X-ray scattering and differential scanning calorimetry. It has also been demonstrated that the exact values of lamellar thicknesses obtained from TEM micrographs strongly depend on the place selected for image analysis.     

Preparation of Ultrahigh Molecular Weight Polyethylene/WS2 Composites for Bulletproof Materials and Study on Their Bulletproof Mechanism

Ultrahigh molecular weight polyethylene (UHMWPE)/WS₂ nanoparticle fibers were prepared by adding inorganic fullerene-like (IF) WS₂ nanoparticles treated by a coupling agent to the precursor solution of UHMWPE. The influence of WS₂ nanoparticles on the microstructure and properties of UHMWPE fibers were characterized by the scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), and mechanical property measurements. The bulletproof performance of the UHMWPE/WS₂ composite was tested by a bullet-shock test, and the bulletproof mechanism of the UHMWPE/WS₂ composite was preliminarily studied. The results showed that WS₂ nanoparticles could be uniformly dispersed in the UHMWPE fiber. After incorporating of WS₂ nanoparticles, the UHMWPE fibers became stiffer and tougher than the pristine ones. In particular, the modulus of the fibers increased from 1203 to 1326 cN/dtex. The introduction of IF-WS₂ nanoparticles led to significantly improved bulletproof performance of UHMWPE fibers.     

Crystallization in Microdomains of a Block Copolymer Comprising Semicrystalline Block Observed by Simultaneous Measurement of SAXS and WAXS with H v‐SALS or DSC

Abstract

Semicrystalline block copolymers provide us with a fascinating model for studying the kinetics of crystallization. We performed the simultaneous measurement of small‐ (SAXS) and wide‐angle (WAXS) x‐ray scattering (SWAXS) with differential scanning calorimetry (DSC), or SWAXS with small‐angle light scattering (H _v‐SALS). The specimen used was polyethylene‐b‐poly(ethylene propylene) (PE‐b‐PEP) with the molecular weight of 44,200. The PE block has the melting point (T _m) at 108°C. We observed the time evolution of crystallization in the lamellar microdomains of PE‐b‐PEP after a temperature drop from 180°C (?T _m) to a variety of temperatures slightly below T _m. The exothermic signal was observed by DSC right after the temperature drop, while the four‐leaf‐clover pattern of H _v‐SALS and the SAXS peaks due to the lamellar microdomains were observed several minutes after the temperature equilibration. The WAXS peaks of (110) and (200) reflection were almost simultaneously detected with the H _v‐SALS and the SAXS peaks at crystallization temperature of 100°C. With the crystallization temperature closer to T _m, the WAXS crystalline signals showed up with longer time lag after the H _v‐SALS and the SAXS peaks began to appear. Interestingly, these phenomena are interpreted as that long‐range order of density fluctuation up to the order of micrometers was generated prior to the formation of crystals with partially ordered phase rather than the instantaneous crystalline nucleation.     

Tribological characteristics of UHMWPE composite and relationship with its compressive behavior

The triboogical characteristics and the mechanics compress behaviors of pure and composite ultra high molecular weight polyethylene (UHMWPE) were investigated using tribological apparatus and universal materials testing apparatus respectively. Results show that there are direct relationships between the sliding friction, wear characteristics, and compression behaviors of UHMWPE composite. The composite of UHMWPE with added copper particles had great improvement in tribological characteristics and mechanics behaviors. Based on the experimental results, a microstructure model of UHMWPE-copper composite is preliminarily proposed.

     

Ab Initio Simulation of Ta2O5: A High Symmetry Ground State Phase with Application to Interface Calculation

It is reported that the recently predicted triclinic γ‐phase ground state Ta₂O₅ by Yang and Kawazoe can be assigned a much more symmetric I4₁/amd space group, and is isomorphic to P‐Nb₂O₅. Interestingly, the well‐known high temperature α‐phase Ta₂O₅ also has the I4₁/amd symmetry, but is unstable at zero temperature according to our phonon dispersion calculation. A thorough energy comparison of the β_AL, δ, λ, Β, L_SR, β_R, Pm, Cmmm, γ, and α phases of Ta₂O₅ is carried out using density functional theory under the generalized gradient approximation (GGA). The GGA‐1/2 method is applied in calculating the electronic structure of various phases, where the tetragonal γ‐phase demonstrates a 4.24 eV indirect band gap, close to experimental value. The high symmetry tetragonal phase together with computationally efficient GGA‐1/2 method greatly facilitates the ab initio simulation of Ta₂O₅‐based devices. As an example, the Ohmic contact nature between metal Ta and Ta₂O₅ by calculating an interface model of b.c.c. Ta and tetragonal γ‐Ta₂O₅, using GGA‐1/2 has been explicitly shown.     

氧等离子体处理对纳米二氧化硅溶胶涂覆高强、高模聚乙烯纤维拉伸性能的影响

基于艾琳方程,提出用于定量分析纤维表面和纳米涂覆层间的纳米界面结构的理论模型.实验结果表明,纤维高分子链段受力塑性变形时,纳米界面结构内纳米微粒阻碍其形貌变化产生热激活体积,该热激活体积是纳米界面结构性能的重要表征;氧等离子体处理对纳米二氧化硅溶胶涂覆高强、高模聚乙烯纤维有增韧作用.由不同处理样品的扫描电子显微镜图片和傅里叶变换红外光谱曲线对比分析可知,经氧等离子体处理纳米二氧化硅溶胶涂覆高强、高模聚乙烯纤维的纳米涂覆层纳米颗粒分布均匀,纳米颗粒还填补纤维表面微观缺陷,活性官能团被引入到纤维表面. 关键词： 激活体积 氧等离子体 高强、高模聚乙烯纤维 纳米界面结构     

Morphology Development in Multi‐Component Polymer Blends: I Composition Effect on Phase Morphology in PP/PET Polymer Blends

The relationship of the phase morphology of polypropylene/polyethylene‐terephthalate (PP/PET) blends and their corresponding compatibilized blends with composition was investigated using digital image analysis. A diameter, d _g , was defined and calculated to discuss the phase morphology of this polymer blend system. A figure‐estimation method was introduced to determine the width of the distribution of d _g . Based on the method, it is proven that the distribution of d _g obeys a log‐normal distribution and consequently, the distribution width, σ was calculated. Further, a fractal dimension, D _f , was introduced to describe the distribution of main sizes of the particles of the dispersed phase. The results showed that, while d _g increased with the concentration of the dispersed phase, σ and D _f show different dependence relations on composition;σ increases monotonously but D _f shows a maximum at a PET content of 30%, indicating that, even though the whole size distribution is much broader, the distribution of the main body of size becomes more uniform when the content of PET is less than 30%.     

X‐ray spectroscopy for chemistry in the 2‐4 keV energy regime at the XMaS beamline: ionic liquids,Rh and Pd catalysts in gas and liquid environments,and Cl contamination in γ‐Al2O3

The 2–4 keV energy range provides a rich window into many facets of materials science and chemistry. Within this window, P, S, Cl, K and Ca K‐edges may be found along with the L‐edges of industrially important elements from Y through to Sn. Yet, compared with those that cater for energies above ca. 4–5 keV, there are relatively few resources available for X‐ray spectroscopy below these energies. In addition, in situ or operando studies become to varying degrees more challenging than at higher X‐ray energies due to restrictions imposed by the lower energies of the X‐rays upon the design and construction of appropriate sample environments. The XMaS beamline at the ESRF has recently made efforts to extend its operational energy range to include this softer end of the X‐ray spectrum. In this report the resulting performance of this resource for X‐ray spectroscopy is detailed with specific attention drawn to: understanding electrostatic and charge transfer effects at the S K‐edge in ionic liquids; quantification of dilution limits at the Cl K‐ and Rh L₃‐edges and structural equilibria in solution; in vacuum deposition and reduction of [Rh^I(CO)₂Cl]₂ to γ‐Al₂O₃; contamination of γ‐Al₂O₃ by Cl and its potential role in determining the chemical character of supported Rh catalysts; and the development of chlorinated Pd catalysts in `green' solvent systems. Sample environments thus far developed are also presented, characterized and their overall performance evaluated.     

Tribological Properties of Polycarbonate Blended with High‐density Polyethylene and High‐density Polyethylene Grafted with Maleic Anhydride

High‐density polyethylene (HDPE) and maleic anhydride grafted HDPE (HDPE‐g‐MA) were selected as lubricant and compatibilizer, respectively, for improving the tribological and mechanical properties of polycarbonate (PC). The morphology of worn surfaces and debris was observed by means of scanning electron microscopy (SEM). The mated steel ring surface was analyzed by using SEM combined with energy dispersive spectroscopy (EDS). Both HDPE and HDPE‐g‐MA reduced the friction and wear of pure PC. HDPE‐g‐MA, which had a better compatibility with PC than HDPE, resulted in better improvement of the mechanical and tribological properties of the PC matrix. A 10 vol. % HDPE‐g‐MA reduced the wear of pure PC by 4 orders of magnitude, and the friction coefficient was reduced from 0.86 to 0.22. Such improvements in the tribological behavior resulted from the good self lubrication of HDPE and HDPE‐g‐MA. The PC/HDPE‐g‐MA (S_90‐0‐10) polyblend also showed higher notched impact strength than pure PC. It may be a useful material for application in tribological fields.     

Formation of adhesive phase onto high strength and modulus PE fiber by PE solution treatment for making PE fiber-reinforced PE composite

The method for the formation of adhesive phase onto polyethylene (PE) fiber surface by passage of the PE fiber through hot PE solutions has been investigated for making composite materials reinforced by the PE fibers. When the PE fiber is treated by the low density PE (LDPE) solution in o-xylene in the range of 120 to 135^°C, the tensile strength of the PE fiber is maintained at that of the original PE fiber. Adhesive strength between the PE fiber surface and LDPE phase formed on the PE fiber through the hot PE solution is found to be so high that the PE fiber itself is torn off. The application of the present method to PE fiber-reinforced PE composites will be expected.     

Dynamic Rheological Behavior of HDPE/UHMWPE Blends

The rheological behaviors of high-density polyethylene (HDPE)/ultra-high molecular weight polyethylene (UHMWPE) blends prepared by melt blending and solution blending were studied. The results showed that the rheological parameters (G′, G ^″, and η*) of both types of blends increased gradually with increasing fraction of UHMWPE, while the tanδ decreased correspondingly. Comparing blends with the same UHMWPE content, all G′, G ^″, and η* values of solution blends were higher, and the tanδ of the solution blends were remarkably lower than those of the melt blends. Combined with the scanning electron microscopy (SEM) observations, it was proved that, because of its very high melt viscosity, the UHMWPE chain is difficult to diffuse and be distributed well in the HDPE matrix by melt blending, resulting in a two-phase-like morphology. On the other hand, the blends prepared by the solution blending showed a homogeneous distribution of UHMWPE in the HDPE matrix. In addition, the state of aggregation of the UHMWPE in the HDPE matrix can be distinguished well by time–temperature superposition (TTS) curves; i.e., the two-phase-like morphology in the melt blends can be detected by the failure of TTS in the high-frequency range, which cannot be reflected by Cole–Cole plots and Han curves.     

Ion Implantation on Ultra High Molecular Weight Polyethylene (Uhmwpe) for Medical Prosthesis

In order to improve the wear resistance of ultra high molecular weight polyethylene (UHMWPE), a surface modification is induced by ion implantation of different ions at 300 keV energy with doses ranging between 10¹⁴ -10¹⁷ ions/cm². Wear measurements, in terms of weight loss, are performed with a “pin on disc” friction machine; these tests measure the wear properly of the UHMWPE against a metallic probe before and after the ion implantation treatment. Results demonstrate that in the implanted samples the wear resistance increases by about 76% with respect to the non-irradiated samples. The irradiated polymeric layer was characterized with the mass quadrupole spectrometry, Raman spectroscopy, infrared absorption analysis, scanning electron microscopy, atomic force microscopy and calorimetric analysis. The results suggest that wear decrease effect can be attributed to the ion bombardment inducing a high carbon surface concentration and cross-linking effects in the irradiated polymeric layer. The irradiated UHMWPE surfaces find special applications in the field of the mobile prosthesis such as hip joints.     

Tribological characteristics of UHMWPE composite and relationship with its compressive behavior

The triboogical characteristics and the mechanics compress behaviors of pure and composite ultra high molecular weight polyethylene (UHMWPE) were investigated using tribological apparatus and universal materials testing apparatus respectively.Results show that there are direct relationships between the sliding friction, wear characteristics, and compression behaviors of UHMWPE composite. The composite of UHMWPE with added copper particles had great improvement in tribological characteristics and mechanics behaviors. Based on the experimental results, a microstructure model of UHMWPE-copper composite is preliminarily proposed.     

Hydrogenated diamond-like carbon film deposited on UHMWPE by RF-PECVD

In this work, investigations were conducted to analyze the properties of diamond-like carbon (DLC) film deposited on ultra-high molecular weight polyethylene (UHMWPE) by radio frequency plasma enhanced chemical vapor deposition (RF-PECVD) at a low temperature of 50 °C. Composition and structure of the films were characterized by scanning electron microscopy (SEM) and Raman spectroscopy. Hardness and wettability of the film were tested. Tribological characterizations were carried out on a universal micro-tribometer, and reciprocating friction against ZrO₂ ball was adopted with 25% bovine serum as lubrication. Results show that DLC film was successfully deposited on UHMWPE surface by RF-PECVD and the sp³ content was about 20% in the film. The film increased the macrohardness of the substrate by about 42% and the wettability was improved too. Tribology test showed a higher friction coefficient but a much smaller wear volume after the deposition due to the surface roughening and strengthening.