Ultrahigh Molecular Weight Polypropylene Research Articles

Facilely prepare ultra-high molecular weight polypropylene loose nanofiltration membrane for efficient dye/salt separation

The simple strategies and processes for preparing nanofiltration (NF) membranes with well-pore channels and high separation efficiency have received growing attention in academia. Herein, ultra-high molecular weight polypropylene (UHMWPP) has been successfully fabricated into high-performance loose NF membranes through thermally induced phase separation (TIPS). The results showed that the as-prepared UHMWPP loose NF membrane has a good water permeance (17.7 L m−2 h−1 bar−1), a high RB rejection (99 %), and a low inorganic salt retention rate (NaCl: 1.9 %), which makes the loose NF membrane a potential choice for dye/salt separation. In addition, the membrane also has good antifouling properties, acid and alkaline resistance, and long-term stability. Thus, this work offers a viable and pragmatic technical approach for addressing high-salt printing and dyeing wastewater, with broad prospects for application and practical value.

On the Mechanical, Thermal, and Rheological Properties of Polyethylene/Ultra-High Molecular Weight Polypropylene Blends.

The novel ultra-high molecular weight polypropylene (UHMWPP) as a dispersed component was melt blended with conventional high-density polyethylene (PE) and maleic anhydride grafted-polyethylene (mPE) in different proportions through a kneader. Ultra-high molecular weight polypropylene is a high-performance polymer material that has excellent mechanical properties and toughness compared to other polymers. Mechanical, thermal, and rheological properties were presented for various UHMWPP loadings, and correlations between mechanical and rheological properties were examined. Optimal comprehensive mechanical properties are achieved when the UHMWPP content reaches approximately 50 wt%, although the elongation properties do not match those of pure PE or mPE. However, it is worth noting that the elongation properties of these blends did not match those of PE or mPE. Particularly, for the PE/UHMWPP blends, a significant drop in tensile strength was observed as the UHMWPP content decreased (from 30.24 MPa for P50U50 to 13.12 MPa for P90U10). In contrast, the mPE/UHMWPP blends demonstrated only minimal changes in tensile strength (ranging from 29 MPa for mP50U50 to 24.64 MPa for mP90U10) as UHMWPP content varied. The storage modulus of the PE/UHMWPP blends increased drastically with the UHMWPP content due to the UHMWPP chain entanglements and rigidity. Additionally, we noted a substantial reduction in the melt index of the blend system when the UHMWPP content exceeded 10% by weight.

Evaluating the molecular weight distribution of ultrahigh molecular weight polypropylene through rheology

This work investigates the possibility of obtaining the molecular weight distribution (MWD) of linear ultrahigh molecular weight (UHMW) polypropylene (PP) through rheology. To this end, the linear viscoelastic response of a set of UHMWPP samples is measured over the largest possible frequency range. The terminal relaxation is achieved by running creep experiments and converting the compliance in dynamic moduli. A time–temperature concentration principle, recently validated for UHMW polyethylene, is also applied to obtain the terminal relaxation of the sample with the largest molecular weight. The linear rheological response is correlated with gel permeation chromatography (GPC) results by means of the mixing rule based on the relaxation modulus. The implementation of such a rule requires the knowledge of some material parameters governing the stress relaxation of the polymer. Since they are unknown in literature for PP, they are estimated from the comparison between the viscoelastic spectra and the GPC distributions of three lab-made UHMWPPs with narrow polydispersity. Such parameters are then used as a basis to predict the MWDs of two UHMWPP samples with large polydispersity. The variability of the parameters upon molecular weight and polydispersity is assessed by applying the mixing rule to two different PP samples with lower molecular weights, one with narrow polydyspersity and another one with broad polydispersity. As the GPC curves of the samples are available, first the direct problem of estimating the rheological response from MWD and then the inverse problem of obtaining the MWD from the rheological data are solved. An overall satisfactory agreement is found between the calculated and measured MWD for the two samples, with both the direct and inverse approach.

Properties of blends of ultra-high molecular weight polypropylene with various low molecular weight polypropylenes

To enhance the ease of processability of the ultra-high molecular weight polypropylene (UHMWPP), the various low molecular weight polypropylenes (LMWPPs) blended with the UHMWPP via a facile melt blending process. The effect of the LMWPPs component on the UHMWPP component on its rheological and mechanical properties was characterized using various measurement techniques. The processability of the UHMWPP was improved drastically with the introduction of LMWPP components as the melt index of the blend increased. As the LMWPP content increases, the mechanical properties of the blends tend to increase or decrease, depending on the type of LMWPP.

Delamination behaviour and surface morphology of wholly thermoplastic composites using different ultra-high molecular weight thermoplastic fabrics with pristine and toughened Elium resin under Mode I loading

Current research investigates the manufacturing and bonding characteristics of wholly thermoplastic composites with thermoplastic fibres and acrylic Elium® resin and toughened Elium®IM with 10% weight acrylonitrile butadiene styrene (ABS) particles under Mode I loading. Ultra-high molecular weight polypropylene (UHMWPP)/Elium® IM and UHMWPP/Elium® composites have shown 43.9% and 24.5% higher critical energy release rate compared to epoxy composite systems, while a similar trend was observed in the case with composites with polyester as the reinforcement system. For ultra-high molecular weight polyethylene (UHMWPE)/Elium®, the increase was only 13.7% but with the use of toughened thermoplastic variant, the increase was found to be 36.8% higher. Detailed microscopic examination reported fibre bridging, pull-out, strong fibre–matrix adhesion, riverlines, and matrix deformation owing to the ductile characteristic of Elium® resin. ABS-modified Elium®IM composites have shown rough matrix fracture surface and there was internal cavitation of ABS particles followed by crack growth and local shear band formation.

On the Mode I and Mode II Delamination Characteristics and Surface Morphological Aspects of Composites with Carbon-Thermoplastic Hybrid Fabrics and Innovative Liquid Thermoplastic Resin.

In the current research, the delamination behavior under Mode I and Mode II loading for the hybrid carbon-thermoplastic fabrics in conjunction with novel liquid thermoplastic acrylic Elium® resin processable at ambient conditions was studied. The experimentation by incorporating doublers methodology, studying the performance under Mode I and Mode II loading, and understanding failure mechanisms using surface morphological fractography is deliberated. Hybrid Carbon-Ultra-high molecular weight polyethylene (UHMWPP)/Elium® composite has shown a 22.81% higher GIC and a 22.2% higher GIIC than Carbon-UHMWPP/Epoxy composite. On the contrary, the Carbon_Ultra-high molecular weight polypropylene (UHMWPE)/Elium® has shown an 11.11% higher Mode I critical energy release rate (GIC) and a 7.58% higher Mode II critical energy release rate (GIIC) than Carbon_UHMWPE/Epoxy composite. Hybrid fiber reinforced thermoplastic composites have shown severe plastic deformation of the matrix, rough fracture surface, and micro-cracks on the de-bonding surface, extensive fiber bridging, and crack branching which contributed to the improvement in the delamination behavior. Hybrid fiber architecture is also found to be detrimental by inducing crack arresting mechanisms including the tortuous crack path and the resin-rich pockets path due to the mismatch of the size of the fiber yarns.

Rheological, Mechanical, and Thermal Properties of Ultrahigh Molecular Weight Polypropylene/Low Molecular Weight Polypropylene Blends

Ultra-high molecular weight polypropylene (UHMWPP), with a molecular weight of more than 106 g/mol, is expected to have superior properties, such as high mechanical strength, high thermal properties, high chemical resistance and outstanding tribological properties. However, UHMWPP has a very poor processability due to its high melt viscosity. Therefore, we aimed to improve processability of UHMWPP by blending it with a low molecular weight polypropylene (LMWPP). We attempted to improve the interfacial miscibility and intermolecular entanglement of the UHMWPP/LMWPP system by using a kneader machine. The addition of LMWPP tended to change the mechanical, thermal, and rheological properties of the blend system.

On the Mode II fracture toughness, failure, and toughening mechanisms of wholly thermoplastic composites with ultra-lightweight thermoplastic fabrics and innovative Elium® resin

Current work presents the first investigation on the Mode II fracture toughness of room temperature curable acrylic Elium® resin and toughened Elium®IM with 10% weight acrylonitrile butadiene styrene (ABS) particle with different thermoplastic fabrics like Ultra-high molecular weight polyethylene (UHMWPE), Ultra-high molecular weight polypropylene (UHMWPP), and polyester. The testing methodology using doublers, performance under Mode II loading and understanding the failure and toughening mechanisms is deliberated. GIIC of UHMWPP/Elium®IM composite was found to be 33.3% higher than that of UHMWPP/Epoxy composite. Polyester/Elium® composites have 27.02% higher GIIC than Polyester/Epoxy composites while Polyester/Elium®IM composites exhibited the highest GIIC which was 17.76% higher than Polyester/Elium® composites. Fractography of toughened Elium®IM composites displayed significant resistance to crack propagation that generated a rough and shear deformed curved layer type of de-bonding surface due to the extra toughening provided by particles which generated the crack deflection and void resulting from cavitation of ABS particles.

Graphene Sheets with Modified Surface by Sodium Lauryl Sulfate Surfactant for Biomedical Applications

This work describes synthesis of graphene sheets with modified surface by sodium lauryl sulfate (SLS) surfactant using one-pot solvothermal reaction method. Effect of sodium lauryl sulfate surfactant amount on surface modification level of graphene sheets was investigated. Ether (-S-OR- at 762 cm-1 - 863 cm-1), thiocarbonyl (=C=S at 1050 cm-1 - 1176 cm-1) and sulfoxide (S-O, Vs and Vas at 1030 cm-1 - 1450 cm-1) functional groups released from sodium lauryl sulfate (SLS) surfactant during solvothermal reaction and attached on the surface of graphene sheets were detected by (attenuated total reflectance-fast Fourier infrared) ATR-FTIR spectroscopy. (Atomic force microscope) AFM observations revealed apparent surface of graphene sheets modified by surfactant molecules with an average multiple profile of graphene nanosheets ≈ 4.8 nm high. This synthesis way of surface modified graphene sheets can be considered as easy, one-step and cheap method for manufacturing of novel biosurface with graphene, as reinforcement for biopolymer coatings such as ultra-high molecular weight polypropylene (UHMWPE), metallic biomaterials (Ti and Ti alloys) and bioceramics as hydroxyapatite (HA).

Classification of acoustic emission signals collected during tensile tests on unidirectional ultra high molecular weight polypropylene fiber reinforced epoxy composites using principal component analysis

The objective of this study is to utilize a mathematical procedure for the evaluation of damage mechanism in ultra high molecular weight polypropylene/epoxy composite (UHMWPP/epoxy) specimen with different configuration based on the analysis of the AE signals of presented. Principal component analysis (PCA) is powerful tool, which utilized for the classification of the monitored AE transients. We worked on epoxy L160 resin, UHMWPP fiber bundle and UHMWPP/epoxy unidirectional specimens, subjected to tensile loading. Using model specimens exhibiting a predominant damage mechanism, correlations were established between the observed damage growth mechanisms and the AE parameter variances result in PCA. Outputs from this study revealed that the PCA is an effective tool for identifying damage modes such as matrix cracking, fibre/matrix debonding, fibre breakage and fibre pull-out in the UHMWPP/epoxy composites. The presence of damage modes in UHMWPP/epoxy composites was proven with scanning electron microscopy (SEM) images.

The Lowering of Strength of the Drawn Tape of Ultra-high-molecular-weight Polypropylene by the Irradiation with Xenon Arc Lamp

It was investigated from a practical point of view the influence of light irradiation on the strength of drawn tape of ultra-high-molecular-weight polypropylene (UHMW-PP) prepared by the gel-casting (GC) method and the gel-like spherulite press (GSP) method. Consequently, it was found that the irradiated GC sheets prepared from 1, 2, 4 and 6 wt.% solutions had different tendencies on the change of strength by ultra-drawing. The ratio of lowering of strength increased with increase in draw ratio of both GC and GSP sheets, especially GC sheet.

The Preparation and Study on Ultrahigh Molecular Weight Polypropylene Gel‐spun Fibers

A novel polypropylene (PP) fiber was prepared by using gel spinning/crystallization from dilute solutions of ultrahigh molecular weight isotactic polypropylene (i‐UHMWPP), and subsequently drawing at various temperatures. The influence of drawing temperature on the properties of the resulted fibers was investigated. We found that the draw‐ability and mechanical as well as crystallization properties of the fibers obtained were dramatically improved with increasing drawing temperature. When the drawing temperature is below the α‐crystal relaxation temperature of PP, which was measured by wide‐angle X‐ray diffraction (WAXD) analysis as 100–120°C, the fibers are characterized by lower crystallinity and smaller crystals with less perfection, resulting in brittle fracture and subsequently poor mechanical durability. With drawing at temperatures above the α‐crystal relaxation temperature of PP, a novel UHMWPP fiber with Young's modulus of 27 GPa and tensile strength of 1.3 GPa was obtained. Higher crystallinity and larger crystals with better perfection and orientation were observed in this fiber.

The influence of chain entanglement density on ultra-drawing behavior of ultra-high-molecular-weight polypropylene in the gel-casting method

The ultra-drawing behavior of ultra-high-molecular-weight polypropylene (UHMW-PP) in the gel-casting method has been investigated by using four kinds of gel-cast sheets prepared from four kinds of solutions of 1.0, 2.0, 4.0 and 6.0wt.% of UHMW-PP. Consequently, it was found that the draw ratio during neck deformation (N.DR.) was related linearly to the inverse root of solution concentration of UHMW-PP. Since this phenomenon was similar to the relationship between the attained maximum draw ratio (λmax) and the solution concentration, it was considered that N.DR. was related linearly to the inverse root of chain entanglement density. And, it was also found that λmax could be defined by the maximum drawing stress (F) around yield point in the 2nd step drawing. On the other hand, no influence of solution concentration on the increasing behavior of strength and modulus with ultra-drawing was detected for the gel-cast sheet prepared from initial solution concentration of above 1wt.%. The reason of this fact was inferred from the increase of the content of shishkebab structure in the gel-cast PE fiber from the high initial solution concentration.

Thermal, Electrical and Mechanical Properties of Ultra-high Molecular Weight Polypropylene and Carbon Filler Composites

Isotactic ultra-high molecule weight polypropylene (UHMWPP) composites filled with multi-wall carbon nanotubes (MWNTs), vapor growth carbon fibers (VGCFs) and short carbon fibers (CFs) were prepared by gelation/crystallization from solutions, in which these aspect ratios of MWNTs, VGCFs and CFs chosen were 500–1000, 50–300 and 5–20, respectively. The thermal, electrical and mechanical properties of these composites were studied in terms of their aspect ratios of the three kinds of fillers. The admixture of the three kinds of carbon filler provided better improvement of thermal property in comparison with neat UHMWPP, and the effect was the most significant for the admixture of MWNTs with the highest average aspect ratio. The electrical conductivity by the admixture of carbon fillers was also sensitive to the aspect ratio. Namely, the electrical conductivity of undrawn UHMWPP-MWNT composite film was the highest, when the filler content of the composites was the same. The conductivities of UHMWPP-VGCF and UHMWPP-CF composites decreased drastically by elongation up to 5 times (λ=5), while the conductivity of UHMWPP-MWNT maintained ca. 10−3 S/cm at λ=5 but further elongation up to λ=20 caused a gradual decrease of the conductivity. Young’s modulus of the UHMWPP-VGCF composites was higher than that of neat UHMWPP films in undrawn and drawn states, while that of UHMWPP-MWNT composites became lower when the composite with 3 wt % MWNT content was elongated up to λ=20. These phenomena indicated that a number of entanglement points of MWNTs within the composite assure electric channels in drawn state but hamper the smooth orientation of UHMWPP chains.

The Influence of Chain Entanglement Density on the Increases in Strength and Modulus with Ultra-drawing of Ultra-high-molecular-weight Polypropylene.

The influence of chain entanglement density on the ultra-drawing of ultra-high-molecular-weight polypropylene (UHMW-PP) has been studied by comparison of the gel-like spherulite pressing method (the GSP method) and the gel-casting method, using two kinds of specimens prepared from 2.0wt% solution of UHMW-PP. The only major difference between the specimens in both methods is the cooling rate of solution. The influence of chain entanglement density in an undrawn specimen on the increase in strength and modulus with ultra-drawing has been discussed. It was found that the slopes of strength and modulus versus draw ratio (DR) were steeper in the gel-casting method. This difference was concluded to be due to the difference of chain entanglement density of undrawn specimens, by considering the fine structure and the maximum draw ratio (λmax). And, it was considered that the differences in the above slopes between both methods could not be explained by the changes of crystalline orientation and crystalline size but by the change of fraction of folded-chain crystals (or extended-chain crystals) with ultra-drawing.

The ultra-drawing behaviour of ultra-high-molecular-weight polypropylene in the gel-like spherulite press method: influence of solution concentration

The influence of solution concentration on ultra-drawing in the gel-like spherulite press (GSP) method has been investigated using four kinds of gel-like spherulite formed from 1.0, 2.0, 4.0 and 6.0% w/w solutions of ultra-high-molecular-weight polypropylene (UHMW-PP). The ultra-drawing behaviour and the increase of strength and modulus are discussed with respect to the effect of chain entanglement density. It was concluded that ultra-drawing in the GSP-method was progressed by the deformation of three-dimensional networks formed by chain entanglements, though there were no (or fewer) connections between the initial gel-like spherulites used as a starting material.

Structure and mechanical anisotropy of cold‐rolled ultrahigh molecular weight polypropylene

AbstractWide angle X‐ray diffraction pole figure, small angle X‐ray scattering (SAXS), and refractive index techniques have been employed to investigate structure and deformation mechanisms in unidirectionally cold‐rolled ultrahigh molecular weight polypropylene (UHMWPP) films. All reciprocal lattice vectors (plane normals) of (110), (040), and (130) were found to populate in the film normal (thickness) direction, suggesting that more than one orientation process must be involved in the deformation. SAXS studies on the cold‐rolled UHMWPP reveal an oriented lamellar structure with its long axis perpendicular to the rolled direction, however, the lamellae are somewhat tilted. Refractive index and tensile measurements were undertaken to determine the optical and mechanical anisotropy of the cold‐rolled UHMWPP films. A similar study was undertaken of unidirectionally rolled conventional polypropylene (PP) for comparison.

Crystal orientation and twinning in cold‐rolled ultrahigh molecular weight polypropylene

AbstractThe mechanisms of plastic deformation in cold‐rolled ultrahigh molecular weight polypropylene (UHMWPP) have been explored by means of wide angle X‐ray (WAXD) pole figures. The melt crystallized UHMWPP slabs were rolled unidirectionally in a two‐roll mill at 408 K as well as in the cross (transverse) direction. In the unidirectional rolling, all reciprocal lattice vectors of (110), (040), and (130) were found to orient preferentially in the film normal (thickness) direction. The cross‐rolling of UHMWPP shows the preferential orientation of the above plane normals in the film thickness direction, but the distribution of poles broadens toward the transverse direction. Such orientation behavior is very different from that of conventional cold‐rolled polypropylene. Various orientation mechanisms involving the orientation of lamellae in the film plane, twinning of the (110) plane and slippage mechanisms have been taken into consideration to account for the observed pole figures. A theoretical simulation has been carried out based on an orientation distribution function approach by introducing a slippage angle along the maximum shear stress in conjunction with intralamellar slip around the transverse direction. This model simulation conforms closely with the experimental WAXD pole figures of the (110), (040), and (130) planes.

Morphology and mechanical properties of ultrahigh molecular weight polypropylene prepared by gelation/crystallization at various temperatures

Films of ultrahigh molecular weight (5.4×106) polypropylene were produced by gelation/crystallization at various temperatures from dilute decalin solutions according to the method of Smith and Lemstra. The temperatures chosen were 20°, 30°, 50°, and 60°C. With increasing the temperature, the long period and crystallinity of the resultant gel film increased. By contrast, when the films were stretched up to 50 } 60 times, the increases in Young's modulus and crystallinity become more significant, as the temperature of the gelation/crystallization became lower. This interesting phenomenon is thought to be due to the dependence of the number of entanglements on the temperatures concerning gelation/crystallization and evaporation of solvent from the gel to form a film.