Ultrahigh Molecular Mass Polyethylene Research Articles

Effect of Molecular Mass on Structure and Properties of Ultra High Molecular Mass Polyethylene

Effect of Molecular Mass on Structure and Properties of Ultra High Molecular Mass Polyethylene

Effect of Molecular Mass on Structure and Properties of Ultra High Molecular Mass Polyethylene

Effect of Molecular Mass on Structure and Properties of Ultra High Molecular Mass Polyethylene

INFLUENCE OF NETWORK ON THE INTERFACIAL DIFFUSION OF MULTILAYER POLYETHYLENE BLENDS

Ultrahigh molecular mass polyethylene(UHMWPE) and statistical copolymer of ethylene and 1-hexene(PEH) were used to prepare UHMWPE/PEH blends with relatively low UHMWPE concentrations.UHMWPE forms network structure in the blends with UHMWPE concentrations above a critical value of c=1 wt%.The influence of the formed UHMWPE network on the interfacial diffusion behaviors of multilayer UHMWPE/PEH blends was investigated by applying small oscillatory shear rheology.The interfacial diffusion coefficients of multilayer UHMWPE/PEH blends were obtained from the rheological data.It is found that the diffusion coefficients are time-dependent and two diffusion regions are distinct before the diffusion reaches the plateaus according to the changes of diffusion exponent n in the relation of D-t n,which implies an approximate Fickian diffusion behavior in region Ⅰ(c 1.0 wt%) and an obvious deviation from the Fickian diffusion behavior in region Ⅱ(c1.0 wt%).With the formation of UHMWPE network in the UHMWPE/PEH blends,deviation from the Fickian behavior for diffusion of multilayer UHMWPE/PEH blends becomes significant.The above results help facilitate the industrial processing of multilayer polyolefins,which is related to the interfacial diffusion.

Thermal characterization of UHMWPE stabilized with natural antioxidants

This work presents a study of the thermal degradation of ultra-high molecular mass polyethylene (UHMWPE) stabilized with natural (-tocopherol and carvacrol) and synthetic antioxidants. Thermogravimetric analysis in dynamic mode was used to determine the apparent activation energies of different samples. The stabilization of UHMWPE with low concentrations (around 0.3%) of -tocopherol is enough to obtain an efficient thermal performance of the polymer. Carvacrol is also a good stabilizer for UHMWPE, but at higher concentration than in the case of -tocopherol. The comparison of apparent activation energy between samples with natural and synthetic antioxidants in similar concentration shows that -tocopherol is a better stabilizer in terms of their thermal performance.

In situ prepared composite of ultrahigh molecular mass PE and PANI

Crystallinity parameters and changes in the crystalline morphology with temperature of an electrically conductive composite containing ultrahigh molecular mass polyethylene (UHMMPE) and polyaniline (PANI) doped with dodecylbenzenesulfonic acid (DBSA) are studied for the first time by using differential scanning calorimetry and wide-angle X-ray diffraction. It is found that during the melting of UHMMPE crystals PANI partially penetrates in the amorphous phase of the matrix polymer. Since the composite is found to be thermally stable up to ca. 270°C, it can be suggested that it would be processable without loosing conductivity at temperatures much higher than the melting temperature of UHMMPE.

Polyethylene powder microcolumn for protein separation prior to HPLC plasma analysis. Application to the determination of copper and zinc

AbstractThree different types of polyethylene powder (PE) were investigated with regard to their ability to adsorb proteins, with the goal of accomplishing plasma deproteinization for further HPLC analysis. Best results were obtained with ultrahigh molecular mass polyethylene The proteins retained by the PE powder were washed out of the column with methanol followed by water. A chromatographic system with the PE column as pre‐column was set up for the determination of copper and zinc in plasma. The plasma sample was injected into the chromatograph, and, on passage through the pre‐column, the proteins were adsorbed onto the PE. While a protein‐free eluate was being sent to the analytical column, by switching the pump channels the pre‐column was being flushed with methanol and water to elute the adsorbed proteins. After washing, the pre‐column was conditioned with the eluent to receive the next sample. Copper and zinc determination was performed by HPLC with photometric detection after post‐column derivatization with 4‐(2‐pyridylazo)resorcinol (PAR). The results, compared with those from flame atomic absorption spectrometry, showed that zinc can be determined by direct injection of the sample, but copper only after dilution. As the copper recovery from undiluted samples was about 65%, it was probably retained together with the proteins. However, on previous dilution of the sample with the eluent (acidic solution of lactic acid) the copper recovery reached 100%. The proposed method is suitable for the HPLC determination of copper and zinc in plasma samples without further sample treatment, in about 30 min.

Ultrahigh Molecular mass Polyethylene/ Carbon Nanotube CompositesCrystallization and melting properties

Abstract Ultrahigh molecular mass polyethylene (UHMMPE) is filled with carbon nano-tubes (CNTs) by solution in the presence of maleic anhydride grafted styrene-(ethylene-co-butylene)-styrene copolymer (MA-SEBS) as a compatibilizer. The UHMMPE/CNT composites crystallized from melt were prepared at a cooling rate of 20C min-1. The melting and crystallization behaviors of UHMMPE/ CNT composites were investigated by differential scanning calorimetry. The results showed that onset melting temperature (T m) and degree of crystallinity (X c) of UHMMPE/CNT composites crystallized from solution are higher than those from melt due to the larger crystalline lamellar thickness. The onset crystallization temperature (T c) of UHMMPE/CNT composites tends to shift to higher temperature region with increasing CNT content in the composites. Tm and Tc of UHMMPE phase in UHMMPE/CNT composites decrease with the addition of MA-SEBS. Moreover, the crystallization rate of UHMMPE phase in UHMMPE/CNT composite is increased due to...

Temperature-modulated differential scanning calorimetric measurements on pre-melting behavior of nascent ultrahigh molecular mass polyethylene

Temperature-modulated differential scanning calorimetric (TMDSC) measurements on nascent ultrahigh molecular mass polyethylene (UHMMPE) in scanning as well as quasi-isothermal mode are presented. From these measurements different processes, which contribute to the modulated heat flow in the pre-melting region, both exothermic and endothermic in character, can be separated. One of them only occur on the first heating of the nascent material. Analysis of quasi-isothermal measurements, performed between 90 and 130 °C, show that there are two slow (exponential) relaxation processes with time constants of 2–5 and 10–100 min, respectively. One, exothermic in character, seems to be connected with irreversible structural changes (crystal thickening and ordering). The low activation energy (ca 40 kJ mol −1) points to a chain diffusion process rather than melting and crystallization. The other process (activation energy 60 kJ mol −1) seems to be endothermic. In the melting region, a slow (>100 min) 3rd relaxation process with high activation energy (300 kJ mol −1) can be separated.

Temperature-modulated differential scanning calorimetric measurements on nascent ultra-high molecular mass polyethylene

Temperature-modulated differential scanning calorimetric (TMDSC) measurements on nascent ultra-high molecular mass polyethylene (UHMMPE) in scanning as well as quasi-isothermal mode are presented. From these measurements, a special irreversible relaxation process in the pre-melting region can be separated, which only occur on the first heating of the nascent material. The frequency dependence of this process yield a characteristic time constant of 6.5 s (or 24 mHz) which fits with the α 2-process known from mechanical measurements. Quasi-isothermal measurements show that there are two slow (exponential) relaxation processes with time constants of 2–5 and several hundred minutes, respectively. The latter is only found in the first run of nascent UHMMPE and seems to be connected with irreversible structural changes (crystal thickening and ordering). The low activation energy (ca. 50 kJ mol −1) points to a chain diffusion process rather than melting and crystallization.

Melt Behaviour of Poly(p-xylylene) (PPX) Coated Gel-spun UHMW-PE Fibers As Revealed by Temperature Modulated DSC

The method of temperature modulated DSC has been applied to obtain additional information about the effect of constraints on the melting behaviour of gel-spun ultra high molecular mass polyethylene (UHMW-PE) fibers coated with a high temperature stable poly(p-xylylene) (PPX) polymer. The underlying signal, corresponding to the normal DSC signal, reveals two endothermic peaks for the coated PE fibers. A shift in the underlying and magnitude signal from 142 to 145°C at 0.1 K min–1 , a relative small magnitude signal, together with a vanishing step-like change in the phase signal with increasing PPX coating layer thickness characterize the constraints in terms of a hindrance of the melting of the unconstrained orthorhombic crystal fraction. The time constant of the melting process can be estimated as larger than the reciprocal angular frequency 1/ω=5 s of the modulation.

Variable-temperature study of a gel-spun ultra-high molecular-mass polyethylene fiber by solid state NMR

Solid-state13C nuclear magnetic resonance (13C NMR) methods have been applied to study a gel-spun ultra-high molecular-mass polyethylene fiber. The mass fractions of the crystalline (orthorhombic and monoclinic), intermediate, and amorphous phases have been determined at temperatures between 296 and 413 K. The mobility of the polymer chains in the crystalline and the intermediate phases have been measured within the same temperature range, 296–413 K. Discussions on the chain conformation and the rate of motion are carried out based on the13C chemical shift and spin-lattice relaxation time, respectively.

Structure-property analysis for gel-spun, ultrahigh molecular mass polyethylene fibers

Abstract The structures of four gel-spun, ultrahigh molecular mass polyethylene fibers have been studied with the techniques of full-pattern x-ray diffraction, small-angle x-ray scattering, powder x-ray diffraction, solid-state 13C nuclear magnetic resonance, differential scanning calorimetry, and optical microscopy. A high molecular mass polyethylene fiber is also studied for comparison. At room temperature these fibers show mainly the common orthorhombic crystals and a small amount of monoclinic crystals in addition to an intermediate, oriented phase and the amorphous phase. The structure parameters of the orthorhombic phase change slightly with fiber processing history. The chains of the intermediate phase have largely a trans-conformation and are oriented preferentially parallel to the fiber axis, but are disordered laterally. The mobility (correlation time) of the carbon atoms of the intermediate phase is higher than that of the crystalline phase by 2 orders of magnitude, but lower than that of the a...

The structure and rheology of molten ultra-high-molecular-mass polyethylene

We report optical scattering and birefringence observations on molten ultra-high-molecular-mass polyethylene (UHMMPE) and correlate these observations with a structure in the melt relating to the original reactor powder. In the quiescent state, pressure annealing can cause the observed light scattering to disappear; however, subsequent flow of the material causes the scattering to develop again. A simple microrheological model is proposed to explain some of the structure, pressure annealing and flow effects that have been observed.

A general model for the diffusion and swelling of polymers and its application to ultra-high molecular mass polyethylene

A numerical scheme is described that can predict the diffusion and swelling of solvents into a one-dimensional polymer slab. The work extends previous models of non-fickian diffusion and incorporates both generalized fickian diffusion and a concentration dependent viscoelastic response of the polymer. Depending on the relative magnitude of different parameters, both broad and sharp concentration profiles are predicted, together with linear or t ½ mass uptake kinetics. The model is found to successfully predict the experimentally determined mass uptake kinetics of ultra-high molecular mass polyethylene exposed to an organic solvent at low and high temperatures. Significant solvent loadings are observed with linear kinetics at low temperature and t ½ kinetics at higher temperatures.

Continuous and discontinuous fatigue crack growth of irradiated ultrahigh molecular mass polyethylene in saline solution at 37�C

To provide data for prosthesis design, the fatigue crack growth resistance of irradiated ultrahigh molecular mass polyethylene (UHMMPE) in saline solution at 37°C was determined from tests performed on compact tension specimens, comparable in size to the components in knee prostheses. The specimens were cyclically loaded by using a sinusoidal wave form at 1 Hz with a minimum-to-maximum load ratio of 0.1. Scanning electron microscopic fractography was used to examine the fracture surfaces. At higher stress levels, the Paris's Law was used to analyse the data, and a striation pattern with each striation corresponding to multi-cycles was observed. At lower stress levels, discontinuous fatigue crack growth was found, a phenomenon which dominated the fatigue life of the material and had not been reported previously in this material. A craze zone ahead of the crack tip was observed, which formed the discontinuous crack growth band with a length relevant to the Dugdale plastic zone length.

Structure of polyethylene gel fibres

The results of the study of ultrahigh molecular mass polyethylene gel fibres are discussed. Mercury porometry was used to determine the total volume of the pores. Contraction phenomena on evaporation of occluded liquids appreciably influence the structural characteristics of the gel fibres. Xerogels possess volumetric homogeneity and are formed like honeycomb cell construction. As a result of even slight deformation factors straightening of the molecular chains in the gel system is possible.