熔融挤出HDPE/EVOH共混物的微观结构及性能

采用高密度聚乙烯(HDPE)接枝马来酸酐(MAH)或甲基丙烯酸缩水甘油酯(GMA)作为增容剂,熔融挤出制备HDPE/乙烯-乙烯醇共聚物(EVOH)共混物.通过扫描电镜观察、气体渗透试验以及力学性能试验,分析增容剂对共混物相容性的影响,并研究共混物的力学性能和阻隔性.结果表明:增容剂能显著提高共混物的相容性.与HDPE相...     

Thermo-mechanical characteristics of thermally aged polyethylene/polypropylene blends

Polyethylene (PE), polypropylene (PP) and their blends have attracted a lot of attention due to their potential industrial applications. Therefore, the current work has been carried out with the main objective of investigating the impact of the thermal aging/treatment and blend ratio (composition range) on the mechanical (tensile and hardness) and thermal characteristics (using thermogravimetric analysis in a dynamic air atmosphere) of PE, PP and PE/PP binary blends. Samples of PE/PP blends containing 100/00, 75/25, 50/50, 25/75 and 0/100 wt.% were prepared via injection moulding technique and thermally treated/aged at 100 °C for 0, 2, 4, 7, 14 days. The tensile measurements indicated that the yield strength and the modulus decrease with increasing PE content. It was also observed that PE, PP and their blends deform in ductile modes. They undergo a uniform yielding over a wide range of deformation, which is followed by strain hardening and then failure. The strain to break for pure PE is found to be much higher than that for pure PP and for their blends, intermediate values have been observed. The hardness measurements have also revealed that increasing PE content in PE/PP blends reduced the hardness value of PP, however, thermal aging at 100 °C has not affected the polymers hardness which holds also true for the tensile properties, showing a good correlation between tested mechanical properties. The thermogravimetric analysis (TGA) in a dynamic air atmosphere and derivative thermogravimetric analysis (DTA) were conducted to study the thermal degradation and stability of thermally unaged and aged PE, PP and PE/PP blends in terms of the initial (T_d and T_d(1%)) and final (T_d(99%)) decomposition temperatures and maximum decomposition rate temperature (T_max). All polymers start to decompose at no less than 365 °C. As for mechanical properties, the blend ratio has affected the thermal properties however, aging time has not.     

Glass-fiber reinforcement of in situ compatibilized polypropylene/polyethylene blends

Polypropylene and low-density polyethylene (LDPE) were melt-blended at proportions 75/25, 50/50, and 25/75 w/w, respectively. These blends were reinforced with two types of glass fibers added at an amount of 20 wt %: the E-type fibers without any surface treatment and the M-type fibers, which were treated with y-methacryloxy propyltrimethoxy silane coupling agent. Poly(propylene-g-maleic anhydride) with 0.8 mol % maleic anhydride content and poly(ethylene-co-vinyl alcohol) with 7.5 mol % vinyl alcohol content were added at a 50/50 w/w proportion as in situ reactive compatibilizers at an amount of 10 wt %. The thermoplastic composite materials have higher tensile strength as well as impact strength compared to the unreinforced blends. The simultaneous process of the in situ blend compatibilization, along with the incorporation of glass fibers in the thermoplastic matrix, leads to a significant improvement of the mechanical properties as compared to the properties of the composite materials with the uncompatibilized matrix. Scanning electron microscopy and micro-Raman spectroscopy have been used to study the adhesion of the thermoplastic matrix onto the glass fibers. Significantly better adhesion characteristics were observed in the composites containing M-type glass fibers, with LDPE adhering the most on the fibers. This better adhesion was reflected in the improved mechanical properties of the composites.     

Transport properties of high-density polyethylene/ethylene propylene diene terpolymer blends

Polymer blends based on high-density polyethylene and ethylene propylene diene terpolymer rubber (EPDM) were prepared. The sorption and diffusion of four aliphatic hydrocarbons through the blends were studied in the temperature range of 28–58 °C. Sulfur, dicumyl peroxide (DCP), and a mixture of sulfur and DCP (mixed) were used as cross-linking agents for the blends. Of the three systems, the peroxide vulcanized blends were found to exhibit the lowest penetrant uptake. This has been explained based on the higher rigidity of the –C–C– networks than the polysulfide linkages. The aliphatic liquid penetration through the matrix increased with increase in the EPDM content in the blend. The experimental observations were correlated with the morphology of the blends. Diffusion and permeation coefficients were calculated from the sorption data. A slight deviation from the Fickian trend was observed for the mechanism of transport with an increase in EPDM in the blends. The molar mass between cross-links and thermodynamic parameters of sorption was determined from the swelling data. The experimental observations were compared with various theoretical models.     

Structure and tensile properties of polypropylene/carbon nanotubes composites prepared by melt extrusion

Polypropylene/carbon nanotubes (PP/CNTs) nancomposites were prepared with a single screw extruder by adding maleic anhydride-grafted poplypropylene (PP-g-MAH) as compatibilizer to polypropylene (PP) with different amounts of carbon nanotubes (CNTs) in the range of 0.1–0.7 wt.%. Structure and morphology of the prepared samples were examined by Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), polarizing light microscopy (PLM) and X-ray diffraction (XRD). The results showed that PP spherulites decreased in size when CNTs were introduced into the polymer. Mechanical properties of the samples were also studied. Tensile tests showed that with increasing amount of CNTs the strain at break decreased whereas the Young’s modulus was improved of 16.41 % to 36.05 % and tensile strength of 36.67 % to 64.70 % compared to pristine PP. The SEM microphotographs showed that majority of the CNTs were dispersed individually and oriented along the shear flow direction.     

Dispersed phase morphology and fractionated crystallization of high-density polyethylene in PET/HDPE blends

The fractionated crystallization of high density polyethylene dispersed in a poly(ethylene terephthalate) matrix at composition of 15 wt-% was studied. The effect of the molecular weight of polyethylene with and without compatibilization was particularly addressed regarding its influence on the morphology of the blends. For non-compatibilized blends, the dramatic influence of the molecular weight of the polyethylene on the viscosity ratio and therefore on the dispersion is reflected on the relative intensities of the twin crystallization peaks of polyethylene that are developed upon cooling. These peaks reflect two sets of particles that are nucleated by more or less active heterogeneities. The influence of the addition of an ethylene-glycidyl methacrylate copolymer on the morphology and on the crystallization of the blends was also investigated. For a high molecular weight polyethylene, the compatibilizer shows less efficiency as far as dispersion is concerned.     

Agro-residue reinforced high-density polyethylene composites: Fiber characterization and analysis of composite properties

The main objective of this research was to study the potential of agro-residues such as wheat straw, cornstalk and corncob as reinforcements for thermoplastics as an alternative to wood fibers. High-density polyethylene (HDPE) composites were prepared with a high content of agro-residues (65 wt.%). Surface chemistry of agro-residues was studied in comparison with wood flour with a view to evaluate its importance in determining the end-use properties of the composites. Surface chemistry showed a more carbon rich surface for wheat straw compared to cornstalk, corncob and wood flour. Thermal degradation characteristics of the fibers were studied to investigate the feasibility of these fibers to the processing point of view. The results showed that the agro-residues starts decomposition as low as 200 °C indicating that they can be processed with thermoplastics having a melt temperature less than 200 °C. Mechanical properties and water absorption properties of the composites were studied to evaluate the viability of these fibers as reinforcements in HDPE. Wheat straw filled HDPE composites exhibited superior mechanical properties compared to cornstalk, corncob and even wood flour filled HDPE, where as cornstalk showed comparable mechanical properties to that of wood flour–HDPE composite. All the composites exhibited a high uptake of water due to the high amount of filler present and incorporation of compatibilizer decreased the water uptake of the composites. It was observed that irrespective of the presence of compatibilizers, flexural properties of the composites were decreased considerably after water absorption.     

An experimental study on conversion of high-density polyethylene and polypropylene to liquid fuel

Clean Technologies and Environmental Policy - Pyrolysis of plastic material is a potential way for the conversion of plastic into hydrocarbon fuel. Thermal and catalytic pyrolysis of high-density...     

The effect of compatibilizers on the morphology of isotactic polypropylene/linear low-density polyethylene blends

The morphology of isotactic polypropylene (iPP)/linear low-density polyethylene (LLDPE) blends, compatibilized with ethylene-propylene block copolymer (EP) and two types of styrene-ethylene/butylene-styrene triblock copolymer (SEBS), one containing maleic anhydride, the other no reactive sites, has been investigated by using small-angle X-ray scattering by evaluating their interface distribution functions. To characterize the crystallization behaviour of the blends, their spherulitic growth rates have been measured under the polarizing microscope and nucleation and crystallization kinetics data have been evaluated. The addition of LLDPE to iPP alone has a pronounced effect on the lamellar morphology of the iPP. Adding compatibilizer to the iPP/LLDPE blend leads to a further decrease of the lamellar thickness. Concurrently the nucleation density increases while the Avrami exponent drops from n2.3 for iPP to n=0.74 for the iPP/LLDPE/SEBS blend. It is concluded that the compatibilizer causes the polyethylene component to become more highly dispersed in the polypropylene matrix.     

Morphological, rheological and mechanical characterization of polypropylene nanocomposite blends

In the present work, the effectiveness of styrene/ethylene-butylene/styrene rubbers grafted with maleic anhydride (MA) and a metallocene polyethylene (mPE) as toughening materials in binary and ternary blends with polypropylene and its nanocomposite as continuous phases was evaluated in terms of transmission electron microscopy (TEM), scanning electron microscopy (SEM), oscillatory shear flow and dynamic mechanical thermal analysis (DMA). The flexural modulus and heat distortion temperature values were determined as well. A metallocene polyethylene and a polyamide-6 were used as dispersed phases in these binary and ternary blends produced via melt blending in a corotating twin-screw extruder. Results showed that the compatibilized blends prepared without clay are tougher than those prepared with the nanocomposite of PP as the matrix phase and no significant changes in shear viscosity, melt elasticity, flexural or storage moduli and heat distortion temperature values were observed between them. However, the binary blend with a nanocomposite of PP as matrix and metallocene polyethylene phase exhibited better toughness, lower shear viscosity, flexural modulus, and heat distortion temperature values than that prepared with polyamide-6 as dispersed phase. These results are related to the degree of clay dispersion in the PP and to the type of morphology developed in the different blends.     

The potential of small-scale fusion experiments and the Gordon-Taylor equation to predict the suitability of drug/polymer blends for melt extrusion

The aim of this study was to investigate the use of small-scale fusion experiments and the Gordon-Taylor (GT) equation to predict whether melt extrusion of a drug with an amorphous polymer produces a stable amorphous dispersion with increased drug dissolution. Indomethacin, lacidipine, nifedipine, piroxicam, and tolbutamide were used as poorly soluble drugs. Drug/polyvinylpyrrolidone (PVP) blends were prepared at a 1:1 mass ratio. Small-scale fusion experiments were performed in a differential scanning calorimeter (DSC) and in stainless steel beakers. Extrusion was performed in a Brabender Plasti-corder. The glass transition temperatures T_g were determined by DSC. Taking an average T_g from the DSC melt, beaker melt, and GT equation accurately predicted the extrudate T_g. Physical stability of beaker melt and extrudate samples was tested by X-ray powder diffraction (XRPD) and DSC after storage at 30°C (beaker melt) or 25°C (extrudate) and less than 10%, 60%, and 75% relative humidity (RH). Beaker melts were amorphous, apart from some residual crystallinity. Extrudates were amorphous after preparation. Except for indomethacin/PVP, which remained amorphous, the crystallinity of beaker melts and extrudates increased only at 75% RH. Recrystallization occurred even when the T_g of the sample was well above the storage temperature. Chemical stability of the beaker melts and extrudates was tested by capillary electrophoresis and high-performance liquid chromatography (HPLC). Stability was slightly improved in the extrudate compared to the beaker melt. In general, the order for rate of dissolution was crystalline drug was less than the physical mixture, which was less than the drug/PVP beaker melt, which was approximately equal to the extrudate. The use of beaker melts allows a conservative estimate of the potential to melt extrude a drug. To predict physical stability, analysis of the T_g must be combined with physical stability experiments.     

Insight into the molecular arrangement of high-density polyethylene polymer chains in blends of polystyrene/highdensity polyethylene from differential scanning calorimetry and Raman techniques

Polystyrene/high-density polyethylene (PS/HDPE) blends were synthesized by melt blending in a single screw extruder. Co-continuity measurements using solvent extraction and scanning electron (SEM) micrographs showed that co-continuity was obtained around 35% PS. Thermal analyses measurements revealed a reduction in crystallinity of the HDPE phase around the co-continuous composition. Raman analyses across the entire composition range of these blends showed an increase in the normalized integral intensities of the 1128 cm(-1) and 1061 cm(-1) stretching vibrations of the HDPE molecules. The presence of all-trans HDPE chains that are not packed into an orthorhombic structure is used to explain the simultaneous occurrence of reduced crystallinity and increased intensity of all-trans HDPE stretch vibrations.     

Mechanical characterization of melt spun fibers from recycled and virgin PET blends

In this study two Poly (Ethylene Terephthalate) (PET) polymers obtained from mineral water bottles and a virgin fiber grade PET polymer were investigated. In order to improve their properties when reprocessed at high temperatures, recycled polymers were blended with virgin one. Thermal and rheological properties of extruded recycled/virgin (PET-V/R) blends showed a good microstructural stability compared to extruded pure recycled polymers. Mechanical behaviour of melt spun fibers obtained from recycled/virgin blends were investigated in static (tensile) and dynamic (DMA) modes and gave interesting properties. Fatigue failure of fibers was also studied and resulting fracture morphologies were analysed by Scanning Electron microscopy (SEM).     

Grafting effects of polypropylene/polyethylene blends with maleic anhydride on the properties of the resulting wood-plastic composites

In the presented study, polypropylene (PP) and high density polyethylene (PE) were blended at the ratios of 80/20 and 20/80 to simulate recycled waste thermoplastic mixtures. The effects of in situ grafting of PP/PE blends with maleic anhydride through the extruder on the mechanical and rheological properties of resulting wood/plastic composites were investigated. Different ratios of PP and PE in the blends created distinct properties in the resulting composites. Grafting of PP and PE blends improved the tensile and flexure properties of the resulting composites. The composites exhibited a reduced water uptake and resultant dimensional swelling due to grafting with maleic anhydride. Grafting of the blends also considerably improved the interfacial bonding and enhanced the dispersion of wood in the matrix, as evidenced by rheological analysis and scanning electron microscopy.     

Theoretical and experimental study of fibre attrition during extrusion of glass-fibre-reinforced polypropylene

On the basis of the experimental observations described in ref. 1, a model has been proposed to analyse the phenomenon of fibre breakage taking place when granules of short-fibre-reinforced thermoplastics are processed in an extruder. This model essentially determines the bending moment experienced by a single fibre, anchored at one end, due to drag forces produced by the flow of molten polymer past it. This model clearly brings out the effects of molten film thickness, screw speed, viscosity of the polymer melt and the fibre orientation relative to the flow direction. It is postulated that the model provides a mechanism for the breakage of fibres exposed by melting of polymer at the solid bed-molten polymer interface. For fibres which are free to move in the molten polymer, buckling introduced by the shearing motion of the molten polymer, as predicted by the Forgacs and Mason model² is responsible for their attrition. Using the extrusion data of ref. 1, the results of the combined use of the two models show good agreement with the experimental observations, in particular the fibre length distribution of various stages of extrusion. This agreement is observed in spite of several assumptions inherent in the model. Finally, the effect of fibre agglomeration on the attrition phenomenon is also studied.     

Controlled and high throughput fabrication of poly(trimethylene terephthalate) nanofibers via melt extrusion of immiscible blends

Immiscible blends of cellulose acetate butyrate (CAB) and poly(trimethylene terephthalate) (PTT) were melt extruded through a two strand rod die. The extrudates were hot-drawn at the die exit at different draw ratios. PTT fibers were obtained by removal of the CAB matrix from the drawn extrudates, and the morphology evolution of the formed fibers was investigated by scanning electron microscopy. PTT nanofibers with an average diameter of 55 nm were produced by controlling the drawing ratio.