Improving foamability of polypropylene by grafting modification

Polypropylene (PP) foam has been considered as a potential substitute for other thermoplastics foams in industrial applications. However, the key concern is the weak melt strength of PP, which leads to a high content of open‐cell structure in PP foams; and, thus, unsatisfactory for a number of applications. In this work, PP was modified by grafting with unsaturated linear polyester (ULP) in a twin‐screw extruder in attempt to improve the melt strength of PP. The grafting reaction on PP and the modified PP were characterized using FT‐IR, DSC, and TGA. The improved foamability was verified by SEM observation. In addition, the rheological behavior of modified PP was investigated using a Hakke rheometer. The results indicated that the melt strength of grafted PP was significantly enhanced, facilitating the foam formation. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 4114–4123, 2006     

Structural analysis of poly(ethylene terephthalate) modified by polypropylene-graft-maleic anhydride from rheological data

During some investigations on compatibilizing poly(ethylene terephthalate) (PET) blends by maleic anhydride–grafted polyolefins (PO-g-MA), the reaction between PET and PO-g-MA and the formation of PO-g-PET were proposed. However, the effect of PO-g-MA on the rheological properties of PET has not been the aim of any specific study. In our study, polypropylene (PP)-g-MA was melt reacted with PET, and the effects of its content and grafting degree on the intrinsic viscosity and linear viscoelastic properties of PET were investigated. The results reveal that the addition of PP-g-MA leads to increasing intrinsic viscosity, which confirms the reaction between PP-g-MA and PET. Rheological measurements suggest that the addition of PP-g-MA improves the elastic behavior and increases the complex viscosity of PET. No shear thinning behavior was observed for any samples, indicating that branching is not widespread. The increase in PP-g-MA content or grafting degree leads to increases in the intrinsic and complex viscosities and improves the elastic behavior. Furthermore, we reported the unusual observation of an increasing viscosity with frequency in modified sa"mples due to the transesterification phenomenon. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 46896.     

A polypropylene/high density polyethylene blend compatibilized with an ethylene‐propylene‐diene monomer block copolymer: Fitting dynamic rheological data by emulsion models with a physical scheme

The dynamic rheological behaviors at 210, 230, and 250 °C are measured by small amplitude oscillatory shear on a rotational rheometer for a polypropylene(PP)/ ethylene‐propylene‐diene monomer(EPDM) block copolymer/ high density polyethylene (HDPE)/blend. The scanning electron microscope (SEM) photomicrographs show the blend has a droplet/matrix, semi‐co‐continuous, co‐continuous morphology respectively at different weight ratios. The Cole–Cole (G″ vs. G′) data of the blends can be fitted by the simplified Palierne's model only for very narrow weight ratios. A physical scheme is proposed that the dispersed droplets are enclosed by EPDM, thus an equivalent dispersed phase is made up of “expanded” EPDM. With this physical scheme the G″ vs. G′ data of the HDPE‐rich blends at 210 °C can be fitted well by Palierne's model. Also with the physical scheme the G″ vs. G′ data of the PP‐rich blends at three temperatures can be fitted well by G–M's model with G* of interface equals to zero. This means the proposed physical scheme is reasonable. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43709.     

Effect of microstructure induced by microcellular injection molding on electromagnetic interference shielding properties

Preparing lightweight and versatile products is the unremitting goal of industry to save resources and energy. Lightweight carbon fiber reinforced polypropylene (CF/PP) composite foams with high-performance electromagnetic interference (EMI) shielding materials were fabricated by microcellular injection molding (MIM) technology. The average length and distribution of CF in CF/PP composite foams were examined. Thanks to the introduction of foaming process, the average CF length of composite foams was 33.98% longer than that of solids, which effectively enhanced the electrical conductivity and EMI shielding properties. The effect of shot size, gas content, and injection rate on the electrical conductivity and EMI properties was investigated. With melt shot size of 2/3 of the cavity volume, gas content of 0.5 wt% N₂ and injection rate of 100 mm/s, optimal cellular structure of the composite material was obtained. The EMI shielding effectiveness (SE) reaches 36.94 dB, which is the highest value achieved by using MIM technology to the best of the authors' knowledge. In addition, the mechanical properties of cellular structure can still maintain good values, with the tensile strength and impact strength improved by 15.3% and 14.03%, respectively.     

Effect of SiO2 on rheology,morphology, thermal,and mechanical properties of high thermal stable epoxy foam

A series of highly thermostable epoxy foams with diglycidyl ether of bisphenol‐A and bisphenol‐S epoxy resin (DGEBA/DGEBS), 4,4′‐diaminodiphenyl sulfone (DDS) as curing agent have been successfully prepared through a two‐step process. Dynamic and steady shear rheological measurements of the DGEBA/DGEBS/DDS reacting mixture are performed. The results indicate all samples present an extremely rapid increase in viscosities after a critical time. The gel time measured by the crossover of tan δ is independent of frequency. The influence of SiO₂ content on morphology, thermal, and mechanical properties of epoxy foams has also been investigated. Due to the heterogeneous nucleation of SiO₂, the pore morphology with a bimodal size distribution is observed when the content of SiO₂ is above 5 wt %. Dynamic mechanical analysis (DMA) reveals that pure epoxy foam possesses a high glass transition temperature (206°C). The maximum of specific compressive strength can be up to 0.0253 MPa m³ kg^?1 at around 1.0 wt % SiO₂. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40068.     

Comparisons of the rheological behaviors of polypropylene and polymethyl methacrylate in a capillary die

In this study, the rheological characteristics of polypropylene (PP) melt at 210, 220, and 230 °C and polymethyl methacrylate (PMMA) melt at 230, 240, and 250 °C in a micro die were investigated. The experiments were performed over a shear rate range of 3 × 10² to 5 × 10³ s^?1 using an advanced twin‐bore capillary rheometer. Dies with diameters of 1.0, 0.5, and 0.25 mm were used. The results indicated that the geometric dependences of the PP and PMMA viscosities were not identical at different shear rates and temperatures and that the micro size effect had a profound influence on the PP viscosity. The analysis demonstrated that the variations in the shear viscosity of the PP and PMMA melts in the micro die were partially attributed to the contribution of the pressure applied to the polymer melts. Additionally, the effect of wall slip on the PP and PMMA viscosities in the tested dies was investigated based on the modified Mooney method. The results implied that wall slip easily occurred in the PP melt flowing through the 0.25 mm die at 210 °C due to the distinct size effect. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134 , 44617.     

Understanding the foamability and mechanical properties of foamed polypropylene blends by using extensional rheology

In this article, the influence of the rheological behavior of miscible blends of a linear and a high melt strength, branched, polypropylene (HMS PP), on the cellular structure and mechanical properties of cellular materials, with a fixed relative density, has been investigated. The rheological properties of the PP melts were investigated in steady and oscillatory shear flow and in uniaxial elongation in order to calculate the strain hardening coefficient. While the linear PP does not exhibit strain hardening, the blends of the linear and the HMS PP show pronounced strain hardening, increasing with the concentration of HMS PP. Related to the cellular structure, in general, the amount of open cells, the cell size, and the width of the cell size distribution increase with the amount of linear PP in the blends. Also mechanical properties are conditioned by the extensional rheological behavior of PP blends. Cellular materials with the best mechanical properties are those that have been fabricated using large amounts of HMS PP. The results demonstrate the importance of the extensional rheological behavior of the base polymers for a better understanding and steering of the cellular structure and properties of the cellular materials. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42430.     

Experimental investigation of the rheological behaviors of polypropylene in a capillary flow

The rheological characterization of polymer melts is strongly related to their material properties. In this study, we focused on the rheological behaviors of a polypropylene (PP) melt through a capillary die. With an advanced twin‐bore capillary rheometer with dies measuring 1.0, 0.5, and 0.25 mm in diameter, experiments were performed over a shear‐rate range of 3 × 10² to 5 × 10³ s^?1 at three temperatures, 210, 220, and 230 °C. The results demonstrate that the geometry dependence of the PP viscosity relied on the die diameter and the temperature of the PP melt. The viscosity values of the PP melt in the 0.25‐mm diameter die were higher than were those in the 0.5‐ and 1.0‐mm dies at 220 and 230 °C. However, the viscosity values in all of the tested dies were similar at 210 °C. The tendency for the viscosity to decrease as the temperature of the polymer melt increased weakened in the 0.25‐mm diameter die. As a result, the pressure applied to the PP melt in the 0.25‐mm diameter die increased; this caused a decrease in the free volume between molecules. On the basis of the Barus equation, the contribution of pressure to the changed viscosity in each die at each of the tested temperatures was calculated and was found to be as high as 32.86% in the 0.25‐mm die at 230 °C. Additionally, the effect of the wall slip on the geometry dependence of the PP viscosity in the tested dies was investigated with a modified Mooney method. The values of the slip velocity revealed that wall slip occurred only in the 0.25‐mm die at 210 °C. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43459.     

Synthesis and aqueous solution properties of hydrophobically modified polyacrylamide

Hydrophobically modified polyacrylamide (HMPAM) is synthesized by a free radical micellar polymerization method with low amounts of anionic long‐chain alkyl, sodium 9‐(and 10)‐acrylamidostearate (NaAAS), which is derived from a renewable resource material, oleic acid. In this progress, the molar ratio of Sodium dodecyl sulfate (SDS) to NaAAS is adjusted, so polymers with different lengths of the hydrophobic blocks (NH = 3 and NH = 6) are obtained. The copolymers are characterized by ¹H NMR, and the polymer weight and polydispersity are determined by gel permeation chromatography. The solution behaviors of the copolymers are studied as functions of concentrations, pH, and added electrolytes by steady‐flow and oscillatory experiments. The viscosities of these HMPAMs increase enormously above the critical concentration (c*). The sample with longer hydrophobic blocks exhibits better thickening effect. The rheological behaviors of aqueous solutions of HMPAMs are also investigated at different pH and brine environments. Low pH or the presence of brine promotes the intramolecular associating of hydrophobes for the both copolymers in semidilute solutions. The introduction of ionizable carboxylic group on the long hydrophobic side chain significantly influences the aggregation behaviors of the copolymers, leading to unique solution behaviors of the poly(AAm/NaAAS) copolymers. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40754.     

Numerical and experimental studies for gas assisted extrusion forming of molten polypropylene

In this study, the experiments of gas‐assisted extrusion (GAE) for molten polypropylene were carried out under different gas pressures, the different extrudate deformations and sharkskin defects of melt were observed. To ascertain the effects of gas on melt extrusion, non‐isothermal numerical simulation of GAE based on gas/melt two‐phase fluid model was proposed and studied. In the simulations, the melt extruded profile, physical field distributions (velocities, pressure drop, and first normal stress difference) were obtained. Numerical results showed that the deformation degree of melt increased with increasing gas pressure, which was in good agreement with experimental results. It was demonstrated that the influence of gas pressure on the melt extrusion could be well reflected by GAE simulation based on gas/melt two‐phase fluid model rather than simplified‐GAE (SGAE) based on full‐slip wall boundary condition used in the past time. Experimental and numerical results demonstrate that the gas pressure induced first normal stress difference is the main reason of triggering flow behavior changes, extrudate deformations, and sharkskin defects of melt. Therefore, the reasonable controlling of gas pressure is a key in practice of GAE, and the gas layer and its influence should be considered in GAE numerical simulation. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42682.     

Preparation and characterization of hyperbranched poly(ether sulfone) and its application as a coating additive for linear poly(ether sulfone)

Hyperbranched poly(ether sulfone) (HPES), a suitable coating additive for improving the rheological properties of linear poly(ether sulfone) (LPES), was easily produced via polymerization of commercially available bisphenol S (A₂ monomer, BPS) and synthesized 2,4′,6‐trifluoro‐phenylsulfone (BB′₂ monomer, TF). During this reaction, fluoro‐ or phenolic‐terminated HPES (F‐HPES or OH‐HPES) could be facilely obtained by controlling the feed mole ratios of the two monomers. The polymerization mode A₂ + BB′₂ was confirmed by analyzing the model compounds and the degree of branching (DB) was calculated systematically. In addition, the synthesized polymers' chemical structures were exhibited by FTIR, ¹H NMR as well as ¹⁹F NMR spectroscopy. Notably, the addition of 1 wt % HPES reduced the melt viscosity and improved the high temperature liquidity of LPES because of its unique spherical shape. Furthermore, the addition of HPES did not have a negative impact on the performance of LPES, which was attributed to the good miscibility between HPES and LPES. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43892.     

Structural,viscoelastic, and vulcanization study of sponge ethylene–propylene–diene monomer composites with various carbon black loadings

In this article, we report the effect of various carbon nanoparticle concentrations on the structural, curing, tan δ, viscosity variation during vulcanization, thermal, and mechanical characteristics of ethylene–propylene–diene monomer polymer sponge composites. The purpose of this study was to develop high‐strength, foamy‐structure polymer composites with an optimum filler to matrix ratio for advanced engineering applications. We observed that the structural, vulcanization, viscoelastic, and mechanical properties of the fabricated composites were efficiently influenced with the progressive addition of carbon content in the rubber matrix. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39423.     

High-viscoelastic graft modified chitosan hydrophobic association polymer for enhanced oil recovery

The conventional partially hydrolyzed polyacrylamide (HPAM) is greatly restricted by its single linear molecular structure in oil reservoirs with severe reservoir conditions such as high temperature and high salt. In this article, the chitosan (CS) grafted imidazoline monomer copolymer (CS-g-AM/AA/NIDA) was prepared from N-maleyl CS (N-MCS), acrylamide (AM), acrylic acid (AA), 1-(2-N-acryloylaminoethyl)-2-oleoyl imidazoline (NIDA) by free radical copolymerization. The structure was determined by means of Fourier transform infrared spectroscopy, ¹H nuclear magnetic resonance spectroscopy, scanning electron microscope, thermal gravimetric analysis, and so forth, which confirmed the successful preparation of the copolymer with good thermal stability. Under the same conditions, compared with HPAM and copolymer CS-g-AM/AA, CS-g-AM/AA/NIDA greatly increased the viscosity of the aqueous solution and exhibited excellent shear stability (viscosity retention rate 15.62, 4.91, and 11.54% at 510 s⁻¹), temperature resistance (the viscosity retention rate reached 50.89, 24.50, and 36.59% at 120°C) and salt resistance (14,000 mg/L NaCl: viscosity retention rate up to 17.27, 8.26, and 14.60%). In addition, core flooding experiments showed that oil recovery could be enhanced by up to 8.08% by CS-g-AM/AA/NIDA. As a natural polymer material, CS has hardly been reported for polymer flooding, and it is expected to replace general polymers in tertiary oil recovery.     

The study of short-shot water-assisted injection molding of short glass fiber reinforced polypropylene

water penetration length and fiber orientation (along the melt flow direction) are important indicators for water-assisted injection molding products of the fiber-reinforced polymer. The effects of melt short shot size, water injection delay time and water injection pressure on these two important indexes are analyzed theoretically and experimentally. The study found that with the increase of the melt short shot size, the extension of the water injection delay time and the increase of the water injection pressure, the water penetration length changed from 216 to 96 mm, 170 to 210 mm, and 215 to 180 mm, respectively. Therefore, it can be known that melt short shot size has the greatest influence on water penetration length, followed by water injection delay time, and finally water injection pressure. Meantime, due to the fiber orientation and change degree of water-assisted injection-molded products along the melt flow direction, the fiber orientation in the water channel layer along the melt flow direction has the highest and lowest change degree, followed by the wall layer and finally the core layer. It can be known that the melt short shot size has the greatest influence on the fiber orientation and the degree of change along the melt flow direction, followed by the water injection delay time, and finally the water injection pressure.     

The Cole–Cole plot for cure: The cure and reversion of natural rubber

Cure rheometry is routinely used in the rubber industry for processability assessment and cure‐time determination. This article examines these rheological outputs in Cole–Cole format to explore what new insights can be gained from this alternative data plot. It differs from the conventional Cole–Cole treatment in its application to a reacting system. The plots described here are therefore of G″(t) vs. G′(t). Initially some attention is directed to the basics of the Cole–Cole treatment and the likely features to be expected when applied to systems undergoing both cure and reversion. This article goes on to consider examples of both by studying a natural rubber vulcanization at temperatures of 160 °C and above. Through the Cole–Cole approach, it is thought possible to identify the competition between intermolecular and intramolecular sulfurization, and between crosslink and main‐chain scission. The approach offers considerable potential to expand the capabilities of cure rheometry. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44085.     

Gelation mechanism and rheological properties of polyacrylamide crosslinking with polyethyleneimine and its plugging performance in air‐foam displacement

Gels based on polyacrylamide crosslinking with polyethyleneimine have attracted attention because of their resulting high strength and good thermal stability. This study investigated the gelation mechanism of the polymeric gel and its plugging performance in air‐foam flooding. An optic microrheology analyzer was used to monitor the gelation process. The crosslinking reaction occurred in two steps, as determined from the elasticity factor curves, and the polymeric gels adopted a semisolid state from solution, as determined from the solid liquid balance curves. The elastic modulus values were higher than the viscous modulus values, indicating that mature gels were elastic‐based materials. The yield stress increased gradually with increasing polymer dosage, which was consistent with the breakthrough pressure and the trend of displacement pressure. The mature gels showed significant thixotropy. In the core displacement test, the preferred injection volume of the gel was 0.1 pore volume, and the stable pressure of the foam flooding was increased by about three times after the core was plugged. The blocking effect for cores with small original permeability was better than that with large permeability. The best blocking resulted from simultaneous treatment of both ends of the cores, followed by front‐end treatment and rear‐end treatment. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45778.     

Viscoelastic rheology in the melting and crystallization domain: Application to polypropylene copolymers

The purpose of this article was to study the relationship between the rheological properties and the crystallization or melting of two polypropylene‐based copolymers used in the welding of the coating of offshore pipelines. The materials microstructure was studied via X‐ray diffraction, scanning electron microscopy, and optical microscopy. Differential scanning calorimetry was used to determine the crystallization and melting properties at different cooling and heating rates. Dynamic rheological analysis was used to define the rheological properties in the molten and in the transition zone from the molten to solid state and inversely. Both experiments (DSC and rheology) were performed under non‐isothermal conditions to allow complete accessibility to the transition zone. Crystallization and melting are both complex processes in which coexist amorphous and crystalline phases in the sample. A correlation between the rheological properties and crystallization was proposed. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44690.     

Melt spun matrix fibers of toughened polypropylene copolymers modified by high energy electrons

Binary blends of polypropylene (PP) and ethylene‐octene copolymer (EOC) are prepared by continuous electron‐induced reactive processing at various mass ratios of the blend components and various doses without adding of any grafting agents. The influence of mass ratio and dose is investigated in order to get the optimum processing behavior of toughened PP as well as optimum properties of resulting fibers. It is found that toughened PP with a PP/EOC blend ratio of 97.5–2.5  mass % can be used advantageously as a matrix component for the process of online spinning of glass fiber/toughened PP hybrid yarns. Such hybrid yarns belong to one of the most advanced production methods for the manufacturing of fiber reinforced thermoplastic composites with an increased mechanical performance. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44011.     

Thermoviscosifying polymers based on polyether prepared from inverse emulsion polymerization

Thermoviscosifying polymers are attractive for enhancing oil recovery owing to their exceptional thickening power as temperature increases. However, the polymers reported to date show inadequacies including obligatory high polymer concentration to get the thermothickening ability because of their low molecular weight (MW), and inconvenient post‐treatment due to the high viscosity after manufacturing. To overcome these drawbacks, inverse emulsion polymerization was used here for preparing polyether‐based thermoviscosifying polymers (TVP‐Ps) by grafting acrylic monomers onto triblock copolymers PEO–PPO–PEO. It was found the MW of final products could reach 8 million Daltons, making them thermoviscosifying at 0.2 wt %. The viscosity of polymerized inverse emulsions was as low as 175 mPa·s, leading to direct dispersing. The TVP‐Ps containing Pluronic F127, F108, F68 all exhibited significant thermothickening behaviors in both aqueous solutions and brines, and the critical thermoassociative temperature could be tuned by changing the nature or amount of Pluronics. After aging at 45 °C for 60 days with equal initial viscosity, TVP‐Ps shows 21% higher viscosity retention than the reference polymer without Pluronic, PAMA, and preliminary core flooding test demonstrated TVP‐Ps can get 2.1% higher incremental oil recovery than PAMA. This work paves a new avenue for scaled‐up preparation and potential use of TVP‐Ps. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 134, 46696     

Effects of polyphosphoric acid (PPA), styrene-butadiene-styrene (SBS), or rock asphalt on the performance of desulfurized rubber modified asphalt

To improve the performance of desulfurized rubber modified asphalt (DRMA), especially its high-temperature performance, three modifiers (including polyphosphoric acid [PPA], styrene-butadiene-styrene [SBS], and rock asphalt) were selected to modify DRMA respectively. The conventional performance, rheological properties, chemical composition, and thermal decomposition were characterized to analyze the performance and modification mechanism of DRMA and its composites. Test results show that, the addition of PPA, SBS, and rock asphalt can all improve the high temperature of DRMA, among which the desulfurized rubber/rock asphalt compound modified asphalt (DRMA-ROCK) has the best high-temperature performance; however, its construction workability, storage stability, and low-temperature performance are poor. In contrast, desulfurized rubber/PPA compound modified asphalt (DRMA-PPA) not only has better high-temperature performance, but also has excellent low-temperature performance, storage stability, and fatigue performance. Fourier infrared spectroscopy (FTIR) test confirms that the modification process of DRMA by these modifiers is chemical modification, and the characteristic peak indexes obtained from FTIR also prove that DRMA-ROCK has better high-temperature performance but poor construction workability from the microscopic point of view. Furthermore, thermogravimetric analysis-differential scanning calorimetry test shows that the addition of rock asphalt improves the thermal stability of DRMA, while PPA and SBS decrease its thermal stability. From the above results, it can be concluded that DRMA-PPA has excellent comprehensive properties.