Melting Point Of Polypropylene Research Articles

The all‐polymer composites and blends made of ethylene–octene copolymer and partially disentangled polypropylene using a new processing approach

AbstractAll‐polymer composites and blends of ethylene–octene copolymer (EOC) and polypropylene (PP) were produced in the extrusion process. They had the same composition (96:4 wt.%), but five different entanglement densities of PP macromolecules. Depending on the processing temperature, below or above the melting point of PP, fibers or spherical inclusions were formed inside the EOC matrix. The production of PP fibers directly during mixing was possible by reducing the entanglement of macromolecules in this polymer. During fiber formation by solid‐state plastic deformation, the crystallinity of PP decreased, especially for the less entangled polymers. The presence of fibers influenced the mechanical properties of the composites, which were different from those of the blends. Both in blends and composites, the matrix was reinforced, but in the composites the effect was stronger and the measured stresses increased with the lower degree of PP entanglement. SAXS and microscopic observations showed that cavitation occurred in the deformed composites. All‐polymer composites, in which the reinforcement was created as a result of polymer deformation with limited entanglements, have properties that are advantageously different from traditional ones, which opens the prospect of their application.

Effects of the simultaneous use of post-industrial polypropylene waste plastic and soybean oil recycling additive on the performance of high-RAP recycled mixtures

Using reclaimed asphalt pavement (RAP) in asphalt concrete (AC) reduces the need for nonrenewable resources. However, excessive RAP can cause premature cracking in pavements due to its stiff and aged nature. To address this issue, studies propose the incorporation of recycling agents (RA) in RAP recycled mixtures. Nevertheless, incorporating RA may reduce mixture's rutting and moisture resistance. Alternatively, incorporating waste plastic in AC can positively balance the RA negative effects. Therefore, this study explores the simultaneous use of polypropylene (PP) waste plastics and soybean oil RA to improve the overall performance of high-RAP mixtures. Due to its high melting point, PP can have different roles in the asphalt mixture depending on the mixing temperature used. To explore that, three different methods of incorporating PP into a high-RAP mixture were attempted. Five different mixtures were developed varying the binder (virgin and modified with RA), and the PP mixing procedure. Then, the mixtures were subjected to performance-based testing procedures (SCB IFIT and HWTT) as well as to boiling test to verify binder-aggregate adhesion. It was confirmed that the use of soybean oil enhances the cracking performance of the high-RAP mixtures, but the rutting and moisture performances were compromised. However, incorporating PP made the mixture more resistant to moisture and rutting in different instances. It was found that pre-heating the aggregates at higher than PP melting point allows a better coating of aggregates by PP, and results in improved binder-aggregate adhesion, leading to better cracking, rutting, and moisture performance of high-RAP mixtures.

Study of the Viscosity and Thermal Characteristics of Polyolefins/Solvent Mixtures: Applications for Plastic Pyrolysis.

Plastic pollution is one of the biggest environmental problems that the world is currently facing. Pyrolysis is a frontier technique aimed at converting plastic waste back into virgin-quality resin. However, the transfer of the waste plastic feed into the pyrolysis reactor must be optimized before the process can be upscaled to a continuous process. In this study, a new solvent that reduces the viscosity of molten plastic was introduced and characterized. The results revealed that the polymers are soluble in the ratio of up to 75 wt % plastic and 25 wt % solvent at 240 °C. The viscosity of pure low-density polyethylene (LDPE), high-density polyethylene (HDPE), and polypropylene (PP) in the solvent was measured in different weight percentages of polymer in solvent (30–80 wt %) and at 160, 180, 200, 220, 240, and 260 °C. The viscosity decreased with the decreasing polymer-weight percentage and with increasing temperature. The viscosity of LDPE/solvent and PPs(isotactic)/solvent is much lower than for HDPE/solvent and PPp(polypropylene impact copolymer)/solvent. Differential scanning calorimetry (DSC) and thermal gravimetric analysis (TGA) were applied to characterize the thermal behavior of LDPE, HDPE, and PP in the solvent in three different weight percentages (25, 50, and 75 wt %). The DSC results indicate that in the mixture of PPs/solvent and LDPE/solvent the melting point of PP and LDPE decreases as the amount of solvent increases. Overall, these results indicate that the selected solvent is an effective agent to prepare waste plastics for pyrolysis.

Functional dyeable polypropylene fabric development and process parameter optimization Part I: Dyeable modified polypropylene development with process parameter optimization

This study aims to develop dyeable modified polypropylene (PP) granules with disperse dye. The optimal dyeable modified PP granule process used polyester as a mixed copolymer. The purpose was to overcome the excessive difference between the polyester material melting point and PP melting point. The development of a low-melting modified co-polybutylene adipate terephthalate (Co-PBAT) was the key point. After the low-melting modified Co-PBAT was presented, PP and a PP grafting maleic anhydride compatibilizer were made into a composite by dual-screw mixing process. The disperse dye dyeability was reached by the molecular behavior of the Co-PBAT chain segment. The prepared material was applied to explore the thermal properties of modified ester pellets and the functional group was verified by Fourier infrared spectroscopy. In this study, the Taguchi method and principal component analysis were used to optimize the process parameter design of two quality characteristics; namely, the color strength and the polymer melt flow index (MFI). According to the results, the multi-quality optimization of the ester pellets consisted of a modified Co-PBAT melting point of 170°C, the modified Co-PBAT content of 9 wt%, the compatibilizer content of 3 wt%, and the mixing temperature of 205°C. The MFI of the regular PP polymer was 28.1 g/10 min, the color strength was 100 K/S. For the optimal process, the MFI of the PP/Co-PBAT dyeable granules was 37.88 g/10 min, and the color strength was 121.31 K/S. It could be observed that the developed polymer had good circulating workability and color strength.

Growth of craze phase and control of void diameter by Laplace-pressure in crazing films

The pore size of voids in crazed polypropylene (PP) was controlled by Laplace-pressure. Void diameter decreased and dropped out at 100 degrees lower temperature from the melting point of PP. These crazed films are adequate to a battery separator for the application. In this work, we attempted to extend the craze phase for high porosity. New voids were generated and grown around existing voids, and the number of voids per unit area was increased while maintaining the average void diameter. Healing temperature of the crazed PP films by Laplace-pressure was 60 °C in air, however 110 °C–135 °C in electrolytic solutions of propylene carbonate, dimethyl sulfoxide, and diethyl carbonate. This craze healing temperature depended on the interfacial tension.

Feasibility Study of Chemical Treatments on Sorghum Fibres for Compatibility Enhancement in Polypropylene Composites

Polypropylene (PP) is one of the biggest petro-polymers, which is used in very wide application nowadays. The environment problem due to materials such as plastics having very long time degradability, and critical petroleum sources have promoted some studies to empowerment of natural resources such as natural fibres for substituting or at least modifying petro-polymers. Because of biodegradability obtained from natural source, sorghum fibers are interesting to be used as filler in PP composites, despite of weak compatibility between them. Surface modification on the sorghum fibers through alkalinization prior to acetylation was aimed to improve the fiber compatibility to PP. The treatments were expected to substitute hydroxyl group in the sorghum fibers, into acetic ester group in order to increase their hydrophobicity as the fillers. Moreover, the treatments were able to unbundle single fibers into micro-fibrillated cellulose (MFC) fibres with increase in crystallinity index. Usage of this MFC fiber as filler in PP leads to improvement of the composite performances such as thermal properties. In this study, Fourier Transformation Infra-Red (FTIR) Spectroscopy, X-ray Diffraction (XRD), Differential Scanning Calorimetry (DSC) and Field-Emission Scanning Electron Microscope (FE-SEM) were used to evaluate the performances of the Sorghum fibers after the treatments and as the filler in the Sorghum fibers/PP composites. The experimental results showed the MFC fibers as the smallest sizes in 5.0 microns and the highest crystallinity index up to 79.1 %, obtained from alkalinization with 2.5 M NaOH prior to acetylation with 17.4 M CH3COOH and the glacial (CH3CO2)2. Compatibility study of the treated Sorghum fibers on PP shows an improvement indicated by a strong interaction between the fibers and PP on morphology observation, increase in melting point of PP from 163.4°C (using virgin Shorgum fibers) into 163.6°C (using treated Sorghum fibers) in DSC measurements.

Creation of a microrelief by thermally stimulated shrinkage of metal-coated polypropylene films

A study was made of the conditions of producing micron-sized reliefs by thermally stimulated shrinkage of metallized commercial biaxially oriented polypropylene films. It was shown that, in annealing within a temperature range close to the polypropylene melting point, the film shrinks in two directions to form folded structures on the surface. The folds are about 2–8 μm in size. The shrinkage and the relief depth depend on the annealing temperature. The relief remains on the film surface after the removal of the aluminum layer.

Characterization of the dynamic friction of woven fabrics: Experimental methods and benchmark results

A benchmark exercise was conducted to compare various friction test set-ups with respect to the measured coefficients of friction. The friction was determined between Twintex®PP, a fabric of commingled yarns of glass and polypropylene filaments, and a metal surface. The same material was supplied to all benchmark participants and the test conditions were prescribed, making the used set-up the most important variable among the laboratories. Tests at ambient temperature as well as tests above the melting point of polypropylene are part of the benchmark, in order to determine both the dry and hydrodynamic friction characteristics. The dependency on sliding velocity, average pressure and temperature was investigated. Systematic differences are observed between the measurements obtained by the different set-ups, which are discussed and related to design characteristics of the devices. The values obtained in this benchmark are comparable and may serve as a reference to evaluate other friction set-ups. The paper concludes with guidelines for the design of a friction tester.

Melting Point Elevation of Isotactic Polypropylene

The melting point of a conventional isotactic polypropylene (PP) was enhanced by a rapid annealing procedure of an extruded sheet composed of β trigonal form crystals having thick lamellae, which was prepared by T-die processing with a specific β-nucleating agent, N,N′-dicyclohexyl-2,6-naphthalenedicarboxamide. Although the melting point of PP with α monoclinic form, prepared by a conventional processing method, is known to be located around at 165°C, the sample obtained by the present technique showed a higher melting point, 170°C. The phase transformation from β-to α-form crystals, retaining the lamellar thickness, was responsible for the melting point elevation.

Multi-Component Composites Based on Polypropylene, Ethylene-Octene Copolymer and Zinc Oxide

Multi-component blends of polypropylene (PP), ethylene-1-octene copolymer (EOC) and zinc oxide (ZnO) are prepared by melt mixing using two-roll mill. Samples prepared by compression moulding have been investigated by using differential scanning calorimeter (DSC). It is found that addition of ZnO particles decreases PP melting point and increases crystallinity degree of PP. ZnO works as nucleation agent for PP by increasing quantity of crystallization centers, but at the same time decreasing structure quality. Because of the structure change mechanical properties are affected. At lower nanoparticle concentration some reinforcement effect I observed, while at higher particles concentration brittlening occurs. Crystalline structure and particles nature increases thermal stability of PP and PP/EOC blends.

Solid-state shear pulverization as effective treatment for dispersing lignocellulose nanofibers in polypropylene composites

Lignocellulose nanofibers (LCNFs) were prepared by the wet-disk milling of wood flour and were subsequently used as a reinforcing filler for a polypropylene (PP) polymer matrix. The specific surface area and the smallest fiber width of the LCNFs were found to be 106 m2/g and 20 nm, respectively. Solid-state shear pulverization (SSSP) using a batch-type kneader was performed at a temperature lower than the PP melting point in order to improve the dispersion of the LCNFs in the PP matrix, which also contained 5 wt% maleic anhydride-grafted PP. The SSSP treatment improved LCNF dispersion; this was determined through optical and scanning electron microscopy observations. The improvement in LCNF dispersion after the SSSP treatment increased the Young’s moduli, yield strengths, and toughnesses of the resulting composites. The composites showed higher Young’s moduli and yield strengths that those of the neat PP matrix; this was true in the case of both the tensile and the bending tests. However, the impact strengths of the composites were not significantly different from that of the neat matrix. Finally, the crystallization rate of the PP matrix also increased with the increase in LCNF dispersion.

Graft Copolymeriztion of Glycidyl Methacrylate/Styrene onto Polypropylene in Solid State

Radical grafting of glycidyl methacrylate (GMA) onto polypropylene (PP) powder was studied in this research. The reaction temperature was below the melting point of PP so that the reaction was carried out in solid state. Styrene (St) acting as electron donor compounds was used as grafting comonomer and xylene was used as interfacial agent to swell the PP powder. The effects of monomer and comonomer concentration on the graft degree were investigated. The FT-IR spectra of the grafted PP demonstrated that GMA and St were grafted onto PP backbone successfully and the polarization optical micrographs showed that the grafted chains acted as nucleating agent and speeded up the crystallization process.

Characterization of carbon black‐filled immiscible polypropylene/polystyrene blends

AbstractThe electrical and rheological behaviors of carbon black (CB)‐filled immiscible polypropylene (PP)/polystyrene (PS) blends were investigated. The compounding sequence influences the phase morphology of the ternary CB/PP/PS composites and the distribution of CB aggregates. Simultaneous measurements of resistance and dynamic modulus were carried out to monitor the phase coalescence of the ternary composites and CB migration and agglomeration in the PS phase during annealing at temperatures above the melting point of PP. The variation of resistivity is mainly attributed to CB agglomeration in the PS phase and the interfacial region, while the variation of dynamic modulus is regarded as the superimposition of the phase coalescence and CB agglomeration in the PS phase. The ternary composites with the majority of CB particles distributed in the interfacial region show the lowest conductive percolation threshold and the most stable resistivity–temperature performance during heating–cooling cycles. Copyright © 2011 Society of Chemical Industry

ANTIOXIDANT DEPLETION AND OIT VALUES OF HIGH IMPACT PP STRANDS

The service life of a polyolefin product depends to large extent on the type and amount of the antioxidants added. During the manufacturing, storage and use of the product the antioxidants are depleted by physical processes and chemical degradation, and this impairs its long-term performance. The initial and in-use oxidation stability is often characterized and monitored by the measurement of the oxidative induction time (OIT), and service life predictions are based on the rate of decrease of the OIT value. To study the correlation between the OIT value and the actual antioxidant concentration, eight random arrays of high-impact polypropylene (PP) strands stabilized using six different antioxidant packages (composed of Irgafos 168, Irganox 1010 and 1330, Chimassorb 944) were immersed in hot water (80°C and 90°C) and oven aged in air (80°C) for more than two years, and the change of OIT values and antioxidant concentrations was measured. For phosphitic and phenolic stabilizers water immersion is generally a more critical aging condition than oven aging in air, while for the hindered amine stabilizers (HAS) the opposite was observed. As expected, a linear correlation between OIT values and concentrations was found for the "classical" package of phosphitic and phenolic stabilizers. In the case of Irganox 1330, the change of the OIT values during aging was considerably slower than the change of concentration. Even when zero concentration was reached according to the vanishing peak height in the chromatogram, a considerable OIT value was still measurable. This may be due to unidentified degradation products of Irganox 1330 which still act as antioxidants in the long run. Addition of HAS (Chimassorb 944) seems to enhance the initial OIT of stabilized phenolic samples and the long-term effectiveness of the phenolic stabilization under air oven aging conditions. However, the marked long-term effectiveness of the HAS itself and the slow change with time of the concentration were not detectable by OIT measurements above the PP melting point of about 170°C.

Modeling of coat‐hanger die under vibrational extrusion

AbstractThe distributions of the pulsatile pressure field, the pulsatile velocity field, and the pulsatile resident time of the polymeric melt in the coat‐hanger die are derived by using the pulsation of volumetric flow rate and pressure. Subsequently, formulae of the manifold radius and the slope of the manifold are deduced via volumetric flow rate pulsation. Polypropylene (PP) was employed for the experiments of the vibrational extrusion. The results indicate that the average extrusion pressure declines with frequency or amplitude decreasing; the distribution of residence time along the width of the coat‐hanger die performs uniformly during the vibrational extrusion process; the theoretical extrusion pressure well agrees with the experimental pressure; the experiments of tensile test, impact test implicate that vibration improves the mechanical properties of products; differential scanning calorimetry testing demonstrates that the melting point of PP is moved to a higher temperature value, and the endothermic enthalpy and the crystallinity are improved as well when superimposing the vibrational force field. Accordingly, the model of the coat‐hanger die under vibrational extrusion is well consistent with the experiments. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Pore Structure of Heat-Treated Nonwoven Materials

The pore structure of heat-treated nonwoven materials is determined by the conditions of heating and cooling them. The effect of the shrinkage properties of a bicomponent fibre on the pore structure of the materials is manifested at a treatment temperature above the melting point of polypropylene.

Effect of Processing Time on the Tensile, Morphological, and Thermal Properties of Rice Husk Powder‐Filled Polypropylene Composites

Brabender plasticorder internal mixer was used to incorporate rice husk powder into polypropylene. Rice husk powder (RHP)‐filled polypropylene (PP) composite was prepared by varying mixing time under constant rotor speed (50 rpm) at two mixing temperatures. Brabender mixing torque, tensile properties, morphology, and thermal properties were investigated in detail. Results indicate that the tensile properties, such as Young's modulus, yield strength, and elongation at break, do not exhibit a significant trend with the increasing of processing time. Scanning electron microscope (SEM) micrographs reveal the better filler dispersion at longer processing time. Differential scanning calorimetry (DSC) analysis indicates nucleating ability of RHP and reduction of degree of crystallinity of PP at higher temperature and longer processing time. In fact, RHP changes the melting point of PP in the composites.

Ductile–brittle‐transition phenomenon in polypropylene/ethylene‐propylene‐diene rubber blends obtained by dynamic packing injection molding: A new understanding of the rubber‐toughening mechanism

AbstractFor a more complete understanding of the toughening mechanism of polypropylene (PP)/ethylene‐propylene‐diene rubber (EPDM) blends, dynamic packing injection molding was used to control the phase morphology and rubber particle orientation in the matrix. The relative impact strength of the blends increased at low EPDM contents, and then a definite ductile–brittle (D–B) transition was observed when the EPDM content reached 25 wt %, at which point blends should fail in the ductile mode with conventional molding. Wide‐angle X‐ray diffraction (WAXD), differential scanning calorimetry (DSC), and scanning electron microscopy (SEM) were used to investigate the shear‐induced crystal structure, morphology, orientation, and phase separation of the blends. WAXD results showed that the observed D–B transition took place mainly for a constant crystal structure (α form). Also, no remarkable changes in the crystallinity and melting point of PP were observed by DSC. The highly oriented and elongated rubber particles were seen via SEM at high EPDM contents. Our results suggest that Wu's criterion is no longer valid when dispersed rubber particles are elongated and oriented. The possible fracture mechanism is discussed on the basis of the stress concentration in a filler‐dispersed matrix. It can be concluded that not only the interparticle distance but also the stress fields around individual particles play an important role in polymer toughening. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 2086–2097, 2002

Effect of Maleic Anhydride Grafted Polypropylene on Structure of Polypropylene/Polyamide 6 Blend Fiber.

The effect of maleic anhydride grafted polypropylene (hereafter MAH-PP) on the structure of blend fibers of polypropylene (PP) and polyamide 6 (PA6) was investigated. Although undrawn fibers of pure PP or PA6 do not show crystalline orientation, undrawn blend fibers without MAH-PP show low crystalline orientation. Moreover, in undrawn blend fibers containing MAH-PP, distinct crystalline orientation of PP was observed. In the case of drawn fibers, blend fibers containing MAH-PP in an amount of 10 phr or more showed broader diffraction peaks of PA6 crystals in wide-angle X-ray diffraction than did blend fibers having an MAH-PP content of 5 phr or less or pure PA6 fibers. Small-angle X-ray diffraction clearly showed that, in all blend fibers, the long period structure does not depend on MAH-PP content. When the blend fibers were annealed at 180°C, which is higher than the melting point of PP, one scattering peak was observed in blend fibers having MAH-PP content of 10 phr or more. In contrast, two scattering peaks were observed in blend fibers having an MAH-PP content of 5 phr or less.

Morphology and Elastomeric Properties of Isotactic Polypropylene/Hydrogenated Polybutadiene Blends

Isotactic polypropylene (PP) was found miscible on a molecular level with hydrogenated polybutadiene (hBR). As there is a possibility of using this blend for designing new types of thermoplastic elastomer (TPE), mechanical properties were measured with the emphasis on elastic behavior. The best elastomeric behavior was found for blends crystallized at room temperature (26°C), while poor elastomeric properties with high modulus were found for blends crystallized at high temperatures (e.g., 120°C). Elastic properties of blends quenched to low temperatures (e.g., 0°C—−73°C) were slightly worse. Transmission electron microscopy showed that the blend crystallized at the high temperature had a crosshatch lamella structure, while the blends crystallized at lower temperatures (below room temperature) had only small fragmented lamellar crystallites. The latter structure of PP is very unique and can be found only under special conditions. The essential may be the presence of high molecular weight impurity, which prevents formation of crosshatch lamellar structure at the high supercooling depths. Fragmented crystals then probably function as tie points for amorphous chains so that good elastomeric behavior can be achieved. There is a certain possibility of improvement in elastic properties, by annealing quenched samples at high temperature close to melting point of PP. In this case, the crystallinity and size of lamellae increased, while the fragmented character of lamellae was preserved.