Effects of processing route on morphology and mechanical behavior of polypropylene in equal channel angular extrusion

Changes of morphology and mechanical behavior of isotactic polypropylene (iPP) due to equal channel angular extrusion (ECAE) were investigated. The iPP specimens were processed for up to two passes in the same direction (route A), with the specimens rotate 180°around loading axis after the previous pass (route C). The macroscopic observation showed that high level of shear strain is introduced in iPP extruded twice in route A. Reflected optical microscopy revealed that the original spherulites are elongated into ellipsoidal shape along the shear direction in route A, and the recovery of the spherulitic shape occurred in iPP extruded in route C. X‐ray diffraction results and the dynamic mechanical analysis showed that the crystalline and amorphous phase are prone to orientation more favorably via route A than route C. The increase of the dynamic storage modulus (E′) indicated that iPP becomes stiffer than other samples when extruded twice in route A. Izod impact testing results demonstrated that the ECAE‐deformed spherulites influence the crack propagation direction. The impact strength of iPP is greatly improved to 490.5 J/m after processed twice in route A, 10 times of that of un‐deformed reference sample. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

An investigation about solid equal channel angular extrusion on polypropylene/organic montmorillonite composite

The solid equal channel angular extrusion (ECAE) process on polypropylene (PP)/organic montmorillonite (OMMT) was carried out. Scanning electron microscopy, polarized optical microscopy, transmission electron microscopy, and X‐ray diffraction were used to observe and characterize the samples structures. Experimental results show that both PP spherulites and OMMT particles were significantly deformed and orientated toward the shearing direction, and OMMT agglomeration particles were broken into needle‐like primary particles, some even exfoliated into nanosilicate layers after twice ECAE processes due to the immense solid shear force. This solid process approach introduces a new way to prepare PP/OMMT nanocomposites. The mechanism of exfoliation between PP and OMMT was also discussed. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Improvement of mechanical properties of polylactide by equal channel multiple angular extrusion

The combination of high strength and toughness is always the goal of high-performance polymer materials for industrial use. This study addresses the potentialities of a solid state equal-channel multiple-angular extrusion (ECMAE) in production of polylactide (PLA) with simultaneous improvement in toughness, strength, and thermal stability. Chain extender Joncryl was used to form PLA with different chain length and morphology (linear or branched PLA). It is demonstrated that simple shear deformation implemented in ECMAE results in formation of an orientation order, an increase in the degree of crystallinity, and the creation of α crystals with an increased degree of perfection. The value of the effects achieved depends on the type of PLA morphology. The best result is observed in the case of linear PLA. ECMAE-modified linear PLA possess the better combination of strength, modulus, and ductility than the branched one. Compared with neat linear PLA, ECMAE-modified linear PLA shows 12%, 26%, 217%, and 40% increase in tensile strength, Young's modulus, strain at break and impact strength, respectively. Additionally, the storage modulus shows an improved thermal stability of ECMAE-modified PLA.     

Polyoxymethylene orientation by equal‐channel multiple angular extrusion

The effect of conditions and routes of deformation in the course of equal‐channel multiple‐angular extrusion (ECMAE) on physical and mechanical properties of polyoxymethylene (POM) have been studied. As deformation routes, Route C (shear planes are parallel, and the simple shear direction of every deformation zone is changed through 180°) and Route E (shear planes are turned through ±45° around the extrusion axis and the normal to the axis, and simple shear direction is changed through 180° or ±90° with respect to the deformation zone) were selected. It has been shown that ECMAE provides the increase of modulus of elasticity E more than twice, tensile strength σ_T increases in four times. At the same time, strain at break ε_b is reduced by 1.5%. The value of the achieved effects depends on the accumulated deformation and the selected deformation route. The best set of physical and mechanical characteristics was observed in the case of Route E. According to SEM data, Route C results in partial pore healing and E provides total pore healing both in longitudinal and transversal direction. The observed effects are related to orientation order formation, increase of cristallinity degree and reduction of structure imperfection of extrudates. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Lamellae orientation and structure evolution of reinforced poly(lactic acid) via equal channel angular extrusion

The aim of this study was to improve the mechanical performance of biodegradable poly(L-lactic acid) through equal channel angular extrusion (ECAE). Changes in morphology induced by the ECAE shear deformation in poly(lactic acid) (PLA) were investigated. Differential scanning calorimeter results suggested a significant improvement in crystallinity of ECAE-deformed PLA depending on its thermal condition and deformation force. Two-dimensional wide angle X-ray diffraction measurement and polarized FTIR spectroscopies of ECAE-deformed PLA revealed a structural network in the crystalline region, and the taut tie molecules (TTMs) connecting lamellae also stretched. Scanning electron microscope results showed that the macro-fibrils were generated, and the oriented structures were arranged along the nominal shear direction at a certain angle. Both the inclined macro-fibrils structure and the oriented TTMs within fibrils were beneficial in improving mechanical performance. Finally, the mechanical property tests showed that the mechanical properties of PLA were improved overall. The tensile strength, elongation, impact strength, and bending strength increased by 28%, 123.8%, 224.3%, and 47.6%, respectively. Meantime, a transition from brittle fracture to ductile fracture was observed from the original PLA billet to ECAE-deformed one. Therefore, the ECAE process represents a promising approach for comprehensively reinforced PLA.     

Structure and properties of polypropylene/high‐density polyethylene blends by solid equal channel angular extrusion

The solid equal channel angular extrusion (ECAE) process on polypropylene (PP)/high‐density polyethylene (HDPE) blends was carried out. Scanning electron microscopy (SEM) was used to observe the sample structures. Results showed that ECAE process could make PP/HDPE blends to produce orientation structure. Impact performance of ECAE‐PP/HDPE samples after ECAE process improved remarkably, especially for ECAE‐PP/HDPE (90/10)‐O whose impact strength reached 91.91 kJ/m², 18.1 times higher than that of pure PP and 11.2 times higher than that of PP/HDPE (90/10). The mechanism of enhancing between HDPE and PP was discussed. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39759.     

Reinforcing effect caused by equal channel multiple angular extrusion of polymers manufactured by the FDM process: Experimental investigation and mathematical modeling

The effect of orientation of the layers of the original structure of polymers produced by fused deposition modeling (FDM) on the reinforcing effect caused by succeeding equal channel multiple angular extrusion (ECMAE) is studied. As test objects, glassy acrylonitrile butadiene styrene copolymer (ABS), glycol‐modified poly(ethylene terephthalate) (PET‐G) and semicrystalline PET are selected, as well as layered composites ABS/PET and ABS/PET‐G. It is demonstrated that ECMAE results in enhancement of microhardness, storage modulus, impact strength. The density, the glass transition temperature, the melting temperature are increased, too. The crystallinity degree of extrudates is enhanced. It is shown that an increment in the mechanical characteristics is better in the case of longitudinal position of the melt layers, as compared to the transversal one. The achieved effects are related to the pore healing, formation of orientation ordering, and enhanced interphase interaction and homogenization of the system in the course of production of layered composites of thermodynamically incompatible polymers. A physical model is suggested that describes the behavior of the layered materials under ECMAE. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45727.     

Effects of equal‐channel,multiple‐angular extrusion on the physical and mechanical properties of glassy polymers

Through the examples of polycarbonate and poly(methyl acrylate), the evolution of the structure and properties of glassy polymers processed by equal‐channel multiple‐angular extrusion (ECMAE) were studied. It was demonstrated that ECMAE allowed the substantial improvement of the set of strain–strength characteristics of these materials, regardless of the direction of loading applied. With the use of the data from scanning electron microscopy, differential scanning calorimetry, and dilatometry, we found that the simultaneous growth in the strength, plasticity, and impact resistance was related to the formation of a net of biaxially oriented polymeric chains, the decrease in the free volume, and the reinforcement of intermolecular interaction. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42180.     

Control of the mechanical and thermal properties of semicrystalline polymers via a new processing route of the equal channel multiple angular extrusion

Deformation routes of equal‐channel multiple angular extrusion (ECMAE) are suggested that allow realization of new combinations of positions of planes and directions of simple shear. The routes are called F, B+C, D+C. Their effect on the structure and the properties of semicrystalline polymers is studied by the example of high density polyethylene, polyoxymethylene, polytetrafluorethylene. It is demonstrated that the enhanced strength and plasticity characteristics and the reduced anisotropy of microhardness in longitudinal and transversal directions are achieved in the series: route C → routes E,F → route B+C → route D+C. The methods of X‐ray structure analysis and dilatometry revealed differences in biaxial oriented fibril structures formed after these ECMAE routes have been applied and in the character of their distribution over preferred directions of orientation. Possibility of realization of bidirectional invar‐effect in rod‐shaped billets is presented. POLYM. ENG. SCI., 54:531–539, 2014. © 2013 Society of Plastics Engineers     

Compressive behavior and deformation kinetics of ultrafine grained aluminum processed by equal channel angular pressing

ABSTRACT

In the present work, the uniaxial compressive mechanical properties of ultrafine grained (UFG) aluminum produced by equal channel angular pressing method were investigated experimentally over a wide temperatures ranging from 77 to 473 K under both quasi-static and dynamic loading conditions. Based on the experimental results, the strain rate, temperature sensitivity, and the apparent activation volume were estimated. The coupling effects of both experimental temperature and applied strain rate on thermal-activated plastic deformation behavior were also investigated. Based on the thermal activation theory, the rate-controlling mechanisms for the UFG aluminum under both quasi-static and dynamic loading conditions were discussed.     

Effect of ultrasound on extrusion of polypropylene/ethylene–propylene–diene terpolymer blend: Processing and mechanical properties

The effects of ultrasonic irradiation on extrusion processing and mechanical properties of polypropylene (PP)/ethylene–propylene–diene terpolymer (EPDM) blends are examined. Results show that appropriate irradiation intensity can prominently decrease die pressure and apparent viscosity of the melt, increase output, as well as increase toughness of PP/EPDM blends without harming rigidity. In case the blends are extruded with ultrasonic irradiation twice, the impact strength of the blend rises sharply at 50–100 W ultrasonic intensity, and amounts to more than 900 J/m, 1.5 times as high as that of blend without ultrasonic irradiation. Scanning electron microscopy observation shows that with ultrasonic irradiation, morphology of uniform dispersed EPDM phase and good adhesion between EPDM and PP matrix was formed in PP/EPDM blend. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 3519–3525, 2003     

Microstructural origin of physical and mechanical properties of ultra high molecular weight polyethylene processed by high velocity compaction

Ultra High Molecular Weight Polyethylene (UHMWPE) is a semi-crystalline polymer with exceptional wear and impact properties, but also a very high melt viscosity, owing to its extremely long chains. Therefore, UHMWPE is non-melt processable and its processing is long and expensive. However, a new process, High Velocity Compaction (HVC), allows processing UHMWPE within short processing times via sintering. Several high velocity impacts are applied to a powder-filled die to provide self-heating. The sintering is then obtained by local fusion/recrystallization. In this study, the physical and mechanical properties of UHMWPE processed by HVC are investigated. Ductile UHMWPE with a high modulus was obtained. The particular microstructure of the material resulting from the sintering by fusion/recrystallization has then been characterized. It appears that mechanical properties of HVC-UHMWPE are governed by the microstructure induced by processing conditions, and hence can be adjusted for a given application.     

Jute fiber reinforced polypropylene produced by continuous extrusion compounding,part 1: Processing and ageing properties

This article addresses the processing and ageing properties of jute fiber reinforced polypropylene (PP) composites. The composite has been manufactured by a continuous extrusion process and results in free flowing composite granules, comprising up to 50 weight percent (wt %) jute fiber in PP. These granules have similar shape and diameter as commercially available PP granules. Rheological analysis shows that viscosity of the compounds follows the same shear rate dependency as PP and is on the same level as glass‐PP compounds. The mechanical properties show very little variation and exhibit strength and stiffness values at the upper range of competing natural fiber reinforced compounds for injection molding. The mechanical performance reduces gradually upon prolonged thermal loading and immersion in water. The low water diffusion coefficient of the 50 wt % jute‐PP composites indicates that the fibers are not forming a continuous network throughout the polymer. The jute fibers exhibit a stabilizing effect against ultra violet irradiation (UV) on PP polymer and, as a consequence, the mechanical properties of jute‐PP composites hardly decrease during an accelerated UV ageing test. Bacteria, fungi, and garden mold grow easily on the compound material, but only have a limited effect on mechanical properties. The resistance to growth of bacteria on the materials surface can be increased using a biostabilizer. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Steady plastic flow of a polymer during equal channel angular extrusion process: Experiments and numerical modeling

Equal channel angular extrusion (ECAE) is a powerful tool to modify microstructure via high plastic deformation without altering sample geometry. This article investigates the behavior of a polypropylene processed by ECAE. A finite element analysis in which the material constitutive law is coupled with damage by means of Gurson‐Tvergaard damage potential allowed to model experimental tests achieved on this material. Such a modeling allows the prediction of the extrusion load, strain and stress fields, and void volume fraction distribution. The need for the use of a back‐pressure is highlighted. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers     

生物降解材料聚（DL）-乳酸剪切变形强韧化研究

研究了等通道转角挤压技术对生物降解材料聚（DL）-乳酸（PDLLA）的增强、增韧。探讨了挤压温度、挤压次数对PDLLA性能的影响。实验表明，随挤压次数增加，材料强韧性提高；挤压温度对材料性能影响明显。经过2次挤压后，PDLLA的弯曲强度由83．3MPa增加到178．7MPa；原始试样弯曲断口呈脆性断裂，强韧化挤压后，断口呈典型韧性断裂特征，强韧性明显提高。扫描电镜观察表明，断口有大量纤维尾端，呈明显纤维化。广角X射线衍射和差示扫描量热分析表明，随挤压次数增加，PDLLA玻璃化转变温度提高，结构更趋稳定。     

Influence of maleated polypropylene on mechanical properties of composite made of viscose fiber and polypropylene

The purpose of this work was to study how viscose fiber behaves in polypropylene (PP) matrix when maleated polypropylene (MAPP) is used as a coupling agent. The influences of processing conditions on composite properties was of interest. Composites were characterized by FTIR and mechanical testing. The most notable result was the effect of the MAPP concentration on the tensile strength of the composites; the tensile strength increased from 40 to 69 MPa when MAPP was added in amounts up to 6 wt % of the fiber weight. The interaction between MAPP and fiber was confirmed with FTIR. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 87: 1895–1900, 2003     

Preparation and characterization of fluorinated polypropylene by reactive extrusion with fluorinated acrylate

The fluorinated polypropylene (PP) was prepared by reactive extrusion, in which PP was grafted with fluorinated acrylate, acrylic acid 2,2,3,3,4,4,5,5,6,6,7,7,8,8,9,9-hexadecafluoro-nonyl ester (HFNAE). The Fourier transformed spectroscopy results confirmed the graft polymerization on PP backbone by the reactive extrusion. The surface tension of these polymer materials and the influence of HFNAE on the crystalline behavior had been investigated with static contact angles apparatus, wide-angle X-ray diffraction (WAXD), differential scanning calorimetry (DSC) and the polarized optical microscope (POM). The surface tension of fluorinated PP was found to be less than that of the untreated polypropylene. The results showed that the fluorinated acrylate (HFNAE) might induce β form crystals when being grafted into PP from the result of WAXD and DSC. The spherule configuration difference between PP and fluorinated PP could be observed with POM photos. The result from the isothermal crystallization kinetic analyses indicated that the speed of the forming nuclear for the regular PP was smaller than that of the fluorinated PP. In addition, the addition HFNAE improved impact strength and thermal stability of PP, but the tensile tension decreased slightly.     

挤出循环对聚丙烯/竹粉复合材料力学及发泡性能的影响

通过双螺杆挤出机对30％(质量分数,下同)竹粉增强聚丙烯(PP/BP)复合材料进行循环加工,研究了挤出循环次数对PP/BP复合材料流变性能、力学性能和发泡性能的影响.结果表明,随着挤出循环次数的增加,PP/BP复合材料的表观黏度(η)先升高后降低,力学性能先增强后减弱,经第6次挤出循环后,其η、弹性模量和弯曲模量比1次...     

Effect of long‐chain branches of polypropylene on rheological properties and foam‐extrusion performances

The effect of modifying polypropylene by the addition of long‐chain branches on the rheological properties and performance of foam extrusion was studied. Three polypropylenes, two long‐chain‐branched polypropylenes and a linear polypropylene, were compared in this study. The modification was performed with a reactive‐extrusion process with the addition of a multifunctional monomer and peroxide. The rheological properties were measured with a parallel‐plate and elongational rheometer to characterize the branching degree. The change from a linear structure to a long‐chain‐branched nonlinear structure increased the melt strength and elasticity of polypropylene. Also, there was a significant improvement in the melt tension and sag resistance for branched polypropylenes. Foaming extrusion was performed, and the effect of the process variables on the foam density was analyzed with Taguchi's experimental design method. For this study, an L₁₈(2¹3⁵) orthogonal array was used on six parameters at two or three levels of variation. The considered parameters were the polypropylene type, the blowing agent type, the blowing agent content, the die temperature, the screw speed (rpm), and the capillary die length/diameter ratio. As a result, the most significant factor that influenced the foam density was the degree of long‐chain branching of polypropylene. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 1793–1800, 2005     

Reactive extrusion processing of polypropylene/SiO2 nanocomposites by in situ synthesis of the nanofillers: Experiments and properties

The concept of a lab-scale developed in situ sol–gel batch process for fabrication of polypropylene (PP)/silica nanocomposites based on a solvent-free silica precursor polymer, a hyperbranched polyalkoxysiloxane (PAOS), has been transferred to a continuous industrially applicable extrusion process. To achieve a suitable process set-up for the continuous in situ synthesis of nanofillers in the PP melt, process parameters are varied. The influence of process parameters on precursor conversion, size and distribution of the formed silica particles and the mechanical properties of the resulting PP nanocomposites is determined. In addition, these materials are compared to conventional silica composites based on melt mixing process. It was found, that a PAOS conversion to silica particles of more than 90% could be realised using a hexadecyl-modified PAOS of 12.5% degree of modification (C₁₆(12.5%)-PAOS) at the given process set-up. Well distributed, small silica particles without any agglomeration were yield in the resulting composites in comparison to application of silica powder.