High Crystalline Polypropylene Research Articles

Microstructure-Crystallization Correlation with Surface Migration of Additives in High-Crystallinity Polypropylene Composites

Microstructure-Crystallization Correlation with Surface Migration of Additives in High-Crystallinity Polypropylene Composites

Experimental and Virtual Studies in Mechanical Applications of PP-RCT Pipes with Armored Materials

The new generation of newly developed materials, namely the high-crystallinity and high temperature polypropylene random copolymer, called PP-RCT, increases the crystalline capability of polypropylene, which allows pipes produced from this material to operate at higher pressures at elevated temperatures. Pressure tests on pipes made of PP-RCT materials show a resistance over a period of 50 years at 7000C (1580 F) 5 MPa (725 psi) compared with 3.2 MPa (464 psi) for standard materials PPR. By reinforcing PP-RCT with aluminum, glass and basalt composite results in a more resistant structure. As a result of the traction tests, it was found that in all three samples the tensile strength exceeds the manufacturer s limit (10 - 12.7 MPa), the values obtained being: st1 = 8 MPa - sample no. 1; st2 = 13 MPa - sample no. 2; st1 = 11 MPa - sample no. 3. The fiber glass insert is less resistant, the best variant being the basal insect sample (st2 = 13 MPa). Elongation at break for specimen no. 3 was recorded at 0.027 mm / mm. Tests on these material combinations were performed for stretching and flexing requests and compared to 3D created virtual models. Simulations of internal pressure behavior were also performed for different material configurations and the results were compared with the experimental data and the data supplied by the manufacturers.

Observation and modeling of environmental stress cracking behaviors of high crystalline polypropylene due to scent oils

Environmental stress cracking (ESC) is a common phenomenon that affects commercially available polymeric materials exposed to liquid agents under external loading, and it is one of the most common causes of their unexpected long-term failure. In this study, ESC behavior of high crystalline polypropylene (HCPP) was studied through modified notched constant tensile load testing using two different scent oils as environmental agents. The relationship between total lifetime of the material and initial stress intensity factor was determined. Despite the similar molecular structures of the scent oils, they caused a remarkable lifetime difference for the material within a certain loading range. Swelling tests were also conducted in order to define diffusion coefficients for the scent oils without any loading. From these results, the diffusion coefficients for the two scent oils into the HCPP were modeled according to the initial stress intensity factor.

Dielectric features of two grades of bi‐oriented isotactic polypropylene

ABSTRACTThe dielectric properties of two grades of bi‐oriented isotactic polypropylene were studied with a variety of techniques: breakdown field measurements, dielectric spectroscopy, thermally stimulated depolarization currents (Is), and direct‐current (dc) conduction I values. Standard polypropylene (STPP) and high‐crystallinity polypropylene (HCPP) films were investigated. Measurements were carried out over a wide temperature range (−150°C/+125°C). The breakdown fields in both materials showed a very small difference. On the other hand, the dielectric losses and dc conduction I values were significantly lower in HCPP. Both materials showed a decrease in the dielectric loss versus temperature in the range 20–90°C; this is favorable for application in alternating‐current power capacitors. The analysis of the dc I value allowed us to find evidence of two main conduction mechanisms: (1) below 80°C in both materials, a hopping mechanism due to the motion of electrons occurred in the amorphous phase, and (2) above 80°C, ionic conduction occurred in HCPP, and hopping conduction occurred in STPP. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42224.

Physical properties of irradiated thermoplastic elastomeric olefins based on (devulcanized rubber)/(high crystalline polypropylene) formulations

This work aims to produce thermoplastic elastomeric olefins based on devulcanized waste rubber (DR) and polypropylene (PP) compatibilized with poly(ethylene‐propylene‐diene monomer) (EPDM). The coupling of DR/PP in varying proportions with EPDM was investigated by Fourier‐transform infrared, X‐ray diffraction, and scanning electron microscopy techniques. A comparative study was established to evaluate the influence of EPDM content and radiation dose on the physical, mechanical, and thermal performance of DR/PP/EPDM composites. It was found that the synergism of EPDM incorporation and irradiation conditions up to 100 kGy remarkably decreased the PP Tm value, indicating a promotion in the PP and radiation sensitivity. J. VINYL ADDIT. TECHNOL., 21:33–41, 2015. © 2014 Society of Plastics Engineers

Thermo-mechanical properties of devulcanized rubber/high crystalline polypropylene blends modified by ionizing radiation

Ground tire rubber (GRT) poses a challenging environmental, economical, and disposal problem in the world because of their crosslinked three-dimensional network structure. Waste rubber from end-of-life passenger car tires was successfully devulcanized by using mechanical–chemical process. The coupling of DR with PP in different proportion was investigated by FTIR, X-ray diffraction and SEM techniques. The mechanical and thermal behaviors of the blends composed of devulcanized rubber (DR) and high crystalline polypropylene (PP) in different proportions were studied. Evaluation of the mechanical and thermal properties of the developed blends, unirradiated and gamma irradiated, was carried out using tensile strength (Ts), elongation at break (Eb), hardness, TGA and DSC measurements.

Replication of Stochastic and Geometric Micro Structures – Aspects of Visual Appearance

Abstract The surface quality of injection molded parts depends on the processing conditions, the cavity surface structure, the runner system, the used polymer and the part geometry. Different replication of the cavity surface structure to the molded part influences its surface function and visual appearance. A descriptive model of the replication process has been developed, taking into account the thickness of the frozen layer during injection. The expected dependencies were proven by systematic injection molding tests with geometric surface micro structures, having depths of 45 or 100 μm and widths from 400 to 2000 μm, that were replicated into high-crystalline polypropylene (HCPP) and polycarbonate (PC). The volumetric structure replication ratio increased with rising mold temperature, melt temperature and cavity pressure. As expected, the mold temperature was dominant for very small micro features. The RMS roughness, determined by confocal microscopy and atomic-force microscopy, was found to be a suitable replication parameter for draw-polished to mirror-finished stochastic cavity surface structures. An abrupt change in wall thickness decelerated the flow front velocity, thus decreased the replicated polymer surface roughness and increased the surface gloss. Moreover, a several micrometer high “surface step” remained, due to the different thickness-dependent shrinkage. This step always ascended from the thicker to the thinner part area. The replication of a mirror-finished mold surface into HCPP was dominated by morphological effects. Local micro shrinkage differences led to micro sink marks, which affected the surface gloss much more than the mold surface structure.

Preparation and properties of carbon nanotube/polypropylene nanocomposite bipolar plates for polymer electrolyte membrane fuel cells

This study aims at the fabrication of lightweight and high performance nanocomposite bipolar plates for the application in polymer electrode membrane fuel cells (PEMFCs). The thin nanocomposite bipolar plates (the thickness <1.2 mm) consisting of multiwalled carbon nanotubes (MWCNTs), graphite powder and PP were fabricated by means of compression molding. Three types of polypropylene (PP) with different crystallinities including high crystallinity PP (HC-PP), medium crystallinity PP (MC-PP), low crystallinity PP (LC-PP) were prepared to investigate the influence of crystallinity on the dispersion of MWCNTs in PP matrix. The optimum composition of original composite bipolar plates was determined at 80 wt.% graphite content and 20 wt.% PP content based on the measurements of electrical and mechanical properties with various graphite contents. Results also indicate that MWCNTs was dispersed better in LC-PP than other PP owing to enough dispersed regions in nanocomposite bipolar plates. This good MWCNT dispersion of LC-PP would cause better bulk electrical conductivity, mechanical properties and thermal stability of MWCNTs/PP nanocomposite bipolar plates. In the MWCNTs/LC-PP system, the bulk electrical conductivities with various MWCNT contents all exceed 100 S cm −1. The flexural strength of the MWCNTs/LC-PP nanocomposite bipolar plate with 8 phr of MWCNTs was approximately 37% higher than that of the original nanocomposite bipolar plate and the unnotched Izod impact strength of MWCNTs/LC-PP nanocomposite bipolar plates was also increased from 68.32 J m −1 (0 phr) to 81.40 J m −1 (8 phr), increasing 19%. In addition, the coefficient of thermal expansion of MWCNTs/LC-PP nanocomposite bipolar plate was decreased from 32.91 μm m −1 °C −1 (0 phr) to 25.79 μm m −1 °C −1 (8 phr) with the increasing of MWCNT content. The polarization curve of MWCNTs/LC-PP nanocomposite bipolar plate compared with graphite bipolar plate was also evaluated. These results confirm that the addition of MWCNTs in LC-PP leads to a significant improvement on the cell performance of the nanocomposite bipolar plate.

The effect of gamma and electron beam irradiation on the thermal and mechanical properties of injection‐moulded high crystallinity poly(propylene)

AbstractIn the present study, the effect of gamma and electron beam (EB) irradiation on the thermal and mechanical properties of high crystalline polypropylene (HPP) was studied. To study the structural modifications of HPP polymer which could occur following these treatments at different doses (20, 40, 60, 80, 100, and 120 kGy) were applied to all samples. Nonirradiated HPP were used as control samples, differential scanning calorimetry analysis, thermogravimetric analysis, and Mechanical tests were carried out to evaluate the effect of both irradiation treatments (EB and gamma irradiation) on HPP samples. Irradiated samples of HPP decreases melting temperature (Tm) of matrix in EB more than in gamma rays up to 5°C. The changes of mechanical properties exhibit different radiation stability towards 60Co‐gamma radiation and EB radiation. This difference reflects much higher penetration of the gamma radiation through the polymeric material as a function of sample thickness. The degradation on polymer properties caused by gamma irradiation was more than that caused by EB irradiation. Next, we compared the effects of gamma and EB irradiation to determine which of these two processes better maintained the integrity of the irradiated product. POLYM. COMPOS., 2008. © 2008 Society of Plastics Engineers.

Mechanical properties of talc- and CaCO3-reinforced high-crystallinity polypropylene composites

Toughening mechanisms and mechanical properties of two high-crystallinity polypropylene (hcPP)-based composite systems, hcPP/talc and hcPP/CaCO3, are investigated. Significant improvement in tensile modulus is observed in the PP/talc composite, but only a moderate improvement is found for hcPP/CaCO3. The introduction of CaCO3 nanoparticles to hcPP helps nucleate a measurable amount of β-phase crystals and results in a significant drop in crystallization temperature, suggesting a possible retardation of hcPP crystallization. In addition, the hcPP/CaCO3 nanocomposite shows more pronounced damping characteristics than that of hcPP/talc, throughout the temperature range studied. A detailed investigation of fracture mechanisms suggests that well-dispersed, highly oriented talc particles cause embrittlement of hcPP. Only when the crack extends toward the edges of the specimen will the crack deflection/bifurcation and microcracking mechanisms initiate. In the case of hcPP/CaCO3, the CaCO3 nanoparticles help trigger massive crazing and shear yielding if the testing speed is in quasi-static. The presence of β-phase crystals around the CaCO3 particles could facilitate the formation of crazes throughout the hcPP matrix. Approaches for toughening hcPP are discussed.

Susceptibility to scratch surface damage of wollastonite- and talc-containing polypropylene micrometric composites

The paper describes the effect of wollastonite and talc on the scratch deformation behavior of low and high crystallinity polypropylenes under identical test conditions. The vertical resolution of atomic force microscopy and lateral resolution of scanning electron microscopy is utilized to examine the characteristics of scratch damage. Contrary to the expectations that high crystallinity and stiffness of polypropylene composites should increase resistance to scratch deformation, the susceptibility to mechanical deformation depends on bonding of mineral particles to the polymer matrix. Scratch deformed regions in neat polypropylenes were free of voids and grooves, while reinforced-polypropylenes exhibited voids and debonding/detachment of filler particles. The severity of plastic deformation in reinforced polypropylenes is a function of debonding/detachment of mineral particles, which is comparatively more for talc-reinforced polypropylenes than wollastonite-reinforced polypropylenes because of the layered structure of talc that encourages delamination. Usage of coating and coupling agents improved the resistance to scratch deformation by promoting adhesion and bonding between the reinforcement and matrix.

Effect of wollastonite and talc on the micromechanisms of tensile deformation in polypropylene composites

Abstract The work presented here describes the effect of wollastonite and talc on the micromechanisms of surface deformation and subsequent propagation into the bulk of low and high crystallinity polypropylenes during tensile straining. The potential of high resolution electron microscopy is utilized to examine deformation processes, and develop deformation mechanism maps. While mineral-reinforced polypropylenes exhibited an increase in tensile modulus, yield strength remained unaffected. Crystallization behavior indicated that the reinforcement minerals increase the rate of nucleation with consequent increase in percentage of bulk crystallinity. The reinforcement of polypropylene with wollastonite or talc alters the primary micromechanism of deformation from deformation bands/crazing in neat polypropylenes to wedge/ridge tearing in mineral-reinforced low crystallinity polypropylene composites. However, wedges were absent in high crystallinity polypropylene composites. The final fracture in reinforced polypropylene occurs by a mixed mode consisting of fibrillation and brittle mode, while crazing–tearing and brittle deformation are fracture modes for neat polypropylenes.

Tensile deformation behaviour of high isotactic polypropylenes

The tensile flow behaviour and deformation processes during uniaxial loading of high isotactic (high crystallinity) polypropylenes have been investigated at various strain rates. The strain rate sensitivity index indicated that long chain high isotactic (high crystallinity) polypropylene (iPP-L) is relatively less sensitive to strain rate than short chain high isotactic (high crystallinity) polypropylene (iPP-S). Deformation bands formed at low strain contributed to the separation of fibrils/microfibrils, and on subsequent increase in tensile strain, the deformation bands developed into an array of closely spaced crazes that multiplied with an increase in strain and strain rate, and grew inwards. Three fracture morphologies were identified in iPP-L: brittle fracture, crazing - tearing, and brittle fracture with ductile pulling of fibrils/microfibrils (quasi-cleavage). In iPP-S, the predominant mode of failure at all displacement rates was brittle fracture. However, at lower displacement rates, smooth and circular voids associated with nucleating particle were randomly present on the brittle fracture surface of iPP-S. Occasional wedges were also observed on the tensile deformed surface of iPP-S. The deformation processes have been depicted in terms of strain rate - strain deformation diagrams.

Atomic force microscopy characterisation of scratch deformation in long and short chain isotactic polypropylenes and ethylene-propylene copolymers

Surface damage induced during the scratch process in two different grades of high isotactic (high crystallinity) polypropylenes, long and short chain, has been examined by atomic force microscopy (AFM) and scanning electron microscopy (SEM). Atomic force microscopy enabled qualitative and quantitative prediction of the extent of scratch damage, by analysing AFM images before and after scratch deformation. Surface deformation induced by the scratch test on long and short chain high isotactic polypropylenes involved the formation of zigzag scratch tracks. Scratch tracks were regular in long chain and irregular/nonuniform in short chain high isotactic polypropylenes. The line profile and section analysis of AFM images indicated that short chain high isotactic polypropylene is more resistant to mechanically induced surface damage than long chain high isotactic polypropylene. Furthermore, a comparison of scratch damage behaviours of high isotactic polypropylenes, low isotactic polypropylenes, and ethylene-propylene copolymers indicated that the resistance to scratch deformation follows the sequence: high isotactic (high crystallinity) polypropylenes > low isotactic (low crystallinity) polypropylenes > ethylene-propylene copolymers.

Understanding the viscoelastic properties of extruded polypropylene wood plastic composites

AbstractThe main goal of this study was to analyze the effect of process additives, that is, maleated polypropylene (MAPP), and a nucleating agent on the viscoelastic properties of different types of extruded polypropylene (PP) wood plastic composites manufactured from either a PP homopolymer, a high crystallinity PP, or a PP impact copolymer using dynamic mechanical thermal analysis. The wood plastic composites were manufactured using 60% pine wood flour and 40% PP on a Davis‐Standard Woodtruder™. Dynamic mechanical thermal properties, polymer damping peaks (tan δ), storage modulus (E′), and loss modulus (E″) were measured using a dynamic mechanical thermal analyzer. To analyze the effect of the frequency on the dynamic mechanical properties of the various composites, DMA tests were performed over a temperature range of −20 to 100°C, at four different frequencies (1, 5, 10, and 25 Hz) and at a heating rate of 5°C/min. From these results, the activation energy of the various composites was measured using an Arrhenius relationship to investigate the effect of MAPP and the nucleating agent on the measurement of the interphase between the wood and plastic of the extruded PP wood plastic composites. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 1638–1644, 2003

Atomic force microscopy assessment of mechanically induced scratch damage in polypropylenes and ethylene–propylene di-block copolymers

Atomic force microscopy (AFM) in tapping mode has been used to determine the extent of surface damage induced during a scratch test in different grades of polypropylenes (PPs) and ethylene–propylene (EP) di-block copolymers. The surface damage is examined for long chain polymeric materials and their respective short chains. The extent of surface damage is evaluated in terms of average surface height of the plastically deformed region, depth of the scratch tracks, and thickness and density of the scratch tracks. The ability of the polymeric materials to resist scratch deformation under identical conditions of scratch test follows the sequence (from maximum resistance to minimum resistance): high crystallinity PPs>low crystallinity PPs>EP di-block copolymers. Also, short chain polymeric materials have greater resistance to scratch deformation than their respective long chain polymers. The scratch tracks are zigzag in PPs and parabolic in EP di-block copolymers with localized plastic flow involving voids. It is interpreted that modulus and yield strength are the determining factors that dictate the scratch resistance of polymeric materials.

Microstructural evolution during tensile deformation of polypropylenes

Tensile deformation processes occurring at varying strain rates in high and low crystallinity polypropylenes and ethylene–propylene di-block copolymers have been investigated by scanning electron microscopy. This is examined for both long and short chain polymeric materials. The deformation processes in different polymeric materials show striking dissimilarities in spite of the common propylene matrix. Additionally, the deformation behavior of long and their respective short chain polymers was different. Deformation mechanisms include crazing/tearing, wedging, ductile ploughing, fibrillation, and brittle fracture. The different modes of deformation are depicted in the form of strain rate-strain diagrams. At a constant strain rate, the strain to fracture follows the sequence: high crystallinity polypropylenes<low crystallinity polypropylenes<ethylene–propylene di-block copolymers, indicative of the trend in resistance to plastic deformation.

Roles of additives in scratch resistance of high crystallinity polypropylene copolymers

AbstractScratch behavior in neat and talc‐filled high crystallinity polypropylene (PP) copolymers containing various additives is investigated using a cosntant load scratch test and two types of indentation tests (Rockwell and Shore D). The talcfilled PP copolymer exhibits high scratch visibilityand scratch depth. The addition of a nucleating agent or lubricant improves the scratch resistance of the talc‐filled PP copolymer. Differential scanning calorimetry, scanning electron microscopy and attenuated total reflectance Fourier transform infrared spectroscopy are used to characterize crystallinity morphology and scratch mechanisms in PP systems. It is found that the scratch resistance of the PP copolymer systems investigated, in terms of scratch depth and scratch visibility, depends mainly on the fracture features generated during the scratch process. The influences of talc, nucleating agent and lubricant on the scratch behavior of PP are discussed.

The Control of Pore Size in Polypropylene/Paraffin Mixtures Using Intercalated Guest SiO2 Particles

This paper discusses the control of fine layer-like pores in high crystallinity polypropylene (PP) films from a mixture of liquid paraffin and silica particles (SiO2) by rolled compression. Mixtures with various ratios were hot rolled, and then paraffin was extracted in organic solvents. The fine structure of these films was investigated by measuring the apparent specific volume, the surface area using the after nitrogen gas adsorption-desorption method, and small angle X-ray scattering (SAXS). Polythene films with mixing ratios with paraffin from 0.10 to 0.50 w/w showed layer-like pores using rolling ratios of 10 to 30 at 115°C. A wide surface area of 160 m2/g was achieved by rolling the films with mixing ratios 0.17 to 0.10 at rolling ratios of 20 to 30. The SiO2 guest was randomly dispersed in paraffin. It was suggested that a regularly spaced structure of polypropylene layers (host) and layer-like pores of 9 nm and 10.5 nm thick, respectively, is formed at rolling ratios of 25 to 30. The SiO2 plays an important role of intercalation through the polypropylene thin layers, oriented by rolled compression.

The Control of Pore Size in Polypropylene/Paraffin Mixtures Using Intercalated Guest SiO2 Particles

This paper discusses the control of fine layer-like pores in high crystallinity polypropylene (PP) films from a mixture of liquid paraffin and silica particles (SiO2) by rolled compression. Mixtures with various ratios were hot rolled, and then paraffin was extracted in organic solvents. The fine structure of these films was investigated by measuring the apparent specific volume, the surface area using the after nitrogen gas adsorption-desorption method, and small angle X-ray scattering (SAXS). Polythene films with mixing ratios with paraffin from 0.10 to 0.50 w/w showed layer-like pores using rolling ratios of 10 to 30 at 115°C. A wide surface area of 160 m2/g was achieved by rolling the films with mixing ratios 0.17 to 0.10 at rolling ratios of 20 to 30. The SiO2 guest was randomly dispersed in paraffin. It was suggested that a regularly spaced structure of polypropylene layers (host) and layer-like pores of 9 nm and 10.5 nm thick, respectively, is formed at rolling ratios of 25 to 30. The SiO2 plays an important role of intercalation through the polypropylene thin layers, oriented by rolled compression.