Augmentation of performance properties of maleated SEBS/TPU blends through reactive blending

Meticulous investigation of reactive blending of maleic anhydride grafted styrene–ethylene–butylene–styrene (SEBS-g-MA) and thermoplastic polyurethane (TPU) is carried out to achieve systems with controllable morphology and superior mechanical properties. Two types of SEBS-g-MA (abbreviated as M1, M2) with different maleic anhydride content were used to separately blend with TPU. Formation of imide group from the interaction of isocyanate and maleic anhydride predicted from the plausible reaction scheme was confirmed through Fourier transform infrared spectroscopy. High tensile strength of the blends along with appreciable elongation at break was witnessed. Morphology analyses using scanning electron microscopy and atomic force microscopy exposed a vivid and homogenous droplet morphology in all the blends presumably due to in situ formation of a suitable copolymer at the interface. Differential scanning calorimetry was used to pursue the thermal characteristics of the blends. Melt-rheological behavior of the blends was examined using a rubber process analyzer. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48727.     

Upcycling of polypropylene with various concentrations of peroxydicarbonate and dilauroyl peroxide and two processing steps

The influence of two peroxides (peroxydicarbonate/dilauroyl peroxide) with various concentrations (10–200 mmol/kg PP) and their effective opportunity to introduce long chain branched (LCB) were investigated. The dependence of a single and double extrusion step and the changes of the properties were studied. Experiments were carried out in a single screw extruder at 180°C for the first extrusion step (modification) and at 240°C for the second extrusion step (processing simulation). Melt flow rate and dynamic rheological properties were studied at a measuring temperature of 230°C. For the definitive determination of long chain branched polypropylene (LCB-PP) served the extensional rheology measurements. The mechanical properties were examined via tensile test and impact tensile test. Summarized, LCB (melt strength) could be observed via extensional rheology for all modified specimens and the mechanical properties were maintained or even improved for the modified samples. Particularly, samples containing dilauroyl peroxide display excellent mechanical properties in this study.     

Effects of lubricants on the rheological and mechanical properties of wood flour/polypropylene composites

The lubricant is an indispensable agent used in wood plastic composites (WPCs) to improve the processing flowability, especially with high wood content. Here, the effects of different lubricating systems on the rheological and mechanical properties of wood flour/polypropylene (WF/PP) composites are investigated. Additionally, several theoretical models are used to describe the rheological behavior. The results show that stearic acid (SA), semirefined paraffin wax (Wax), and zinc stearate (ZnSt) can decrease the equilibrium torque, complex viscosity, relaxation time, and flow activation energy of the composite melts. Compared to a single lubricant, the combination of Wax and SA lubricants exhibits lower values and the composite with 3 wt % SA and 1 wt % Wax has the best lubricating effect. The synergistic effect of the combined SA and Wax lubricants further decreases the interactive force between the molecules, indicating that multifunctional lubricating systems play a predominant role in WPCs and improve the overall processing properties. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47667.     

Rheological behavior of bitumen modified by reclaimed polyethylene and polypropylene from different recycling sources

This work studied the rheological, thermal, and mechanical properties of bitumen modified by reclaimed polyethylene (PE), and polypropylene (PP) from different recycling sources. The rutting resistance under high temperature of polymer modified bitumen (PMB) was investigated by rheologically temperature ramp test and multiple stress creep recovery (MSCR) test. It is found that for some modified bitumen, a plateau of complex modulus G^* could be formed with temperature increment, revealing rheological stability. Furthermore, these samples with rheological stability revealed a higher creep recovery and lower creep compliance measured by the MSCR test. Glass transition temperature (T_g) measured by dynamic mechanical analysis was used to evaluate the crack resistance under a low temperature of PMB. The influence of recycled PE on the T_g of modified bitumen was different from that of recycled PP modified bitumen, as compared with corresponding virgin polymer modified bitumen. A possible reason for the various effect of recycling sources on the service property of modified bitumen was explored by crystallization and melting behaviors of polymer in bitumen since that polymer with higher crystallinity degree could endow the modified bitumen stiffness, which was closely, related to their service property especially the rutting resistance.     

Theoretical and experimental assessment of UV resistance of high-density polyethylene: Screening and optimization of hindered amine light stabilizers

Hindered amine light stabilizers (HALS) are widely used chemical stabilizers for preventing polymer degradation. In this study, the effects of type of HALS and its content in high-density polyethylene (HDPE) over the stabilization process are investigated employing density functional theory (DFT) and experimental approach. The electrophilicity index of four types of commercial HALS are compared by DFT to select the most effective one. Besides, the HDPE sample containing a phenolic antioxidant and different contents of the selected HALS are experimentally exposed to UV irradiation. The effect of HALS content on the changes in chain microstructure and molecular weight of HDPE are evaluated using gel permeation chromatography and frequency sweep rheometry. In the absence of HALS, HDPE suffers degradation and the phenolic antioxidant causes chain scission. However, by adding HALS, the chain branching and crosslinking mechanisms are predominant. The results of FTIR, DSC, and tensile analyses follow similar trends, revealing that the best stabilization performance corresponds to adding 600 ppm HALS to HDPE.     

Improving melt strength of polypropylene by minimal branching and blending

Branched polypropylenes (PPb) with markedly improved melt strength were produced without significantly affecting the processability of the original PP. A two-step process of functionalization with MA and crosslinking with m-XDA was used, both by batch mixing and by extrusion. Branching degrees of ~0.06 LCB/1000 monomer units or smaller were obtained. All PPbs display clear and significant strain hardening, being the PPb obtained by extrusion the one that shows the largest melt strength. This polymer has a zero-shear-rate viscosity slightly smaller than that of PP while its strain-hardening index is about 10 times higher. Moreover, the nonlinear behavior of PP at elongation begins at a time similar to its terminal relaxation time or larger, while the ratio of these times reduces significantly with branching. PP/PPb blends were prepared to extend the range of obtainable melt strength in PP. They display rheological behavior between those of the mixed polymers with slight positive deviation. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 137, 48845.     

Thermorheological behavior analysis of mLLDPE and mVLDPE: Correlation with branching structure

In this article, the correlation between the thermorheological behavior and the molecular structure of two grades of metallocene polyethylene, namely linear low density and very low density polyethylene, is studied. The investigated polymers possess the same molecular weight and polydispersity index, but different levels of short branches. Increasing the number of short branches results in enhanced activation energy and delayed relaxation times of the polymers. Four methods including the time–temperature superposition (TTS), van Gurp‐Palmen and activation energy (E_a) as a function of the phase angle, E_a(δ), and the storage modulus, E_a(G′) are employed to study the thermorheological behavior of the samples. The results indicated that the thermorheologically simple behavior is dominant in the specimens. Both the E_a(δ) and E_a(G′) showed independency toward phase angle and the storage modulus. Moreover, the activation energy values obtained from the TTS principle and the E_a(δ) and E_a(G′) diagrams were in good agreement. The zero‐shear rate viscosity of the samples also followed the equation of the linear polyethylene. Regarding the simple thermorheological behavior and the agreement of the zero shear rate viscosity with the relation of the linear polyethylene, one can conclude that long branches do not exist in the investigated metallocene polyethylenes of this article. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Looking back to interfacial tension prediction in the compatibilized polymer blends: Discrepancies between theories and experiments

Prediction of interfacial tension of compatibilized polymer blends is a challenging open problem, where experiments and theories hardly support each other. In this work, constitutive models proposed for quantifying the interfacial tension of compatibilized polymer blends were revisited and their limitations/capabilities were discussed. In view of available data in the literature, which could provide with possibility of comparison between interfacial tension values obtained in this work and those published before, high‐density polyethylene (HDPE)/polyamide‐6 and HDPE/polyethylene‐co‐vinyl alcohol pairs comprising varying amounts of HDPE‐g‐maleic anhydride compatibilizer precursor were prepared for obtaining model parameters. The inability of theories in monitoring the interfacial tension was accordingly uncovered. However, outcomes from both theoretical and experimental data provided some insights for elucidating the interplay between interfacial tension and rheological characteristics of the studied compatibilized blends. It was also attempted to uncover the relationships between particle size, particle size distribution, and rheological properties of blends compatibilized with different amounts of HDPE‐g‐maleic anhydride precursor. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46144.     

Nonlinear influences of process parameters on mechanical properties of physically foamed,fiber-reinforced polypropylene parts

The importance of foam injection molded components in industrial applications increases, above all driven by sustainability concerns. In practice, their applicability almost exclusively depends on their mechanical behavior, which is still difficult to predict based on their microstructure. This work aims to present an approach based upon phenomenological observations. From a processing perspective, the objective is to describe the direct processing-properties-relationship. Therefore, this work focuses on the effects of different processing parameters on selected final mechanical properties of foam injection molded components using glass fiber-reinforced polypropylene. A full factorial, central composite design allows for the detection of nonlinear effects, the application of response surface methodology, and the creation of contour plots. Considering three important process parameters (mold temperature, degree of foaming, delay time) and—for the automotive industry—highly important mechanical properties in bi- and uniaxial bending, the results show a detailed picture of individual dependences, but also two-dimensional interactions between the different process parameters. Improvements of more than 140% in absorbed energy and flexural stiffness were obtained at constant part weight. Modulus and strength were increased by 37 and 44%, respectively.     

Cellulose/polypropylene composites: Influence of the molecular weight and concentration of oxidatively degraded and maleated polypropylene compatibilizers on tensile behavior

To improve interactions between fibrous cellulose (FC) and polypropylene (PP), oxidatively degraded polypropylene (DgPP) and maleated polypropylene (MAPP) were studied as compatibilizers. Both compatibilizers had the same mechanism, using esterification between the OH group in FC and the reactive (γ‐lactone, acid, and maleic anhydride) groups in the compatibilizers. However, the adhesion style with the ester bond was considerably different because of the arrangements of the reactive groups. DgPP had reactive groups at the polymer chain end, and the tensile behavior of the FC/PP/DgPP composite exhibited comparatively ductile behavior. However, MAPP had inner reactive groups, and the tensile behavior of the FC/PP/MAPP composite was quite brittle. Observation of these fracture surfaces suggested that the adhesion performance of the interface between FC and PP was strongly influenced by the arrangements of the reactive group. In addition, the performance was influenced by the molecular weight of DgPP and by the content of maleic anhydride groups in MAPP. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Influence of filler treatment on the behavior of blast furnace slag filled polypropylene compounds

Blast furnace slag (BFS) is a byproduct of the blast furnace in iron industry. Due to its composition and structure, BFS is suggested as a promising functional filler that can potentially improve the property profile of polypropylene. To overcome the lack of compatibility between BFS and polypropylene (PP), two coupling agents, vinylethoxysiloxane homopolymer silicon and methacryloxypropyltrimethoxysilane, are utilized for treating the BFS surface. The influence of each coupling agent on the BFS–PP compound properties is investigated in this work. It is observed that both coupling agents equally increase the complex shear viscosity and thermal conductivity of the modified BFS compounds by 10% and 12%, respectively, compared to their unmodified counterparts. The degree of crystallinity of the modified compounds also increased by more than 25%. While the tensile stiffness and yield strength levels are found to be comparable for all compounds, the strain at break of some modified BFS compounds is doubled. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46535.     

Utilization of polyethylene terephthalate waste as a carbon filler in polypropylene matrix: Investigation of mechanical,rheological, and thermal properties

Polyethylene terephthalate (PET) waste was converted into carbon and the feasibility of utilizing it as a reinforcing filler material in a polypropylene (PP) matrix was investigated. The carbon produced by the pyrolysis of waste PET at 900°C in nitrogen atmosphere contains high carbon content (>70 wt%). PP/carbon composites were produced by melt blending process at varying loading concentrations. Scanning electron microscopy images at the fractured surface revealed that the carbon filler has better compatibility with the PP matrix. The mechanical, thermal, and rheological properties and surface morphology of the prepared composites were studied. The thermogravimetric analysis studies showed that the thermal stability of the PP/carbon composites was enhanced from 300 to 370°C with 20 wt% of carbon. At lower angular frequency (0.01 rad/s), the storage modulus (G′) of PP was 0.27 Pa and those of PP with 10 and 20 wt% carbon was 4.06 and 7.25 Pa, respectively. Among the PP/carbon composite prepared, PP with 5 wt% carbon showed the highest tensile strength of 38 MPa, greater than that of neat PP (35 MPa). The tensile modulus was enhanced from 0.9 to 1.2 GPa when the carbon content was increased from 0 to 20 wt%.     

Morphological correlations to mechanical performance of hydroxyapatite‐filled HDPE/UHMWPE composites

Melt mixed and injection molded hydroxyapatite (Hap) filled high‐density polyethylene/ultrahigh molecular weight polyethylene composites were assessed for their thermal, structural, morphological, and mechanical attributes. Differential scanning calorimetry was conducted to analyze the effect of Hap loading on various thermal transitions and their associated enthalpies. The microstructural attributes were characterized by conducting wide angle X‐ray diffraction and scanning electron microscopy (SEM) of cryo‐fractured surface. SEM micrographs of tensile fractured surface revealed the systematic reduction in the size of microfibrils indicating the suppression of local deformation. Improvement in low‐strain mechanical response and flexural properties accompanied with a consistent decrease in strain‐at‐break and toughness was witnessed with increasing Hap content. Toughness aspects were critically discussed in the realms of quasi‐static, dynamic mechanical and sudden impact testing approach. Dynamic mechanical analysis demonstrated the presence of prominent α and γ transitions in the crystalline and amorphous phase respectively. Tensile fractured surface morphologies of the investigated composites revealed a switch‐over from matrix dominated plastic deformation to Hap controlled quasi‐brittle fracture. Thus, our study fundamentally deals with the feasibility of designing polyethylene/Hap composites with superior mechanical properties for biomedical applications, especially for orthopedic implants. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41251.     

Melt strength,local velocity,and elongational viscosity profiles of low‐density polyethylene filaments affected by the die design and process conditions

An experimental arrangement to simultaneously measure the melt strength, velocity profiles, and elongational viscosity profiles across the cross section of a molten filament that emerged from either a circular or slit die for low‐density polyethylene (LDPE) under nonisothermal and isothermal conditions is proposed. The proposed experimental rig was based on a parallel coextrusion technique of colored LDPE melt layers into an uncolored melt flowing from the barrel into and out of a die to form a continuous filament before they were pulled down by mechanical rollers until the filament failed. The experimental rig was also equipped with a high‐speed data‐logging system and a personal computer for real‐time measurements. The results suggest that the draw‐down forces changed continuously with changing roller speed, and the velocity profiles of the melt were not uniform across the LDPE filament during the stretching of the melt. Greater draw‐down forces and local melt velocities were obtained in the slit die or under the nonisothermal condition. The draw‐down forces and velocity profiles in both dies were affected by the volumetric flow rates from the extruder and the roller speeds used, with the effect being more pronounced for the circular die. The elongational viscosity profiles of the LDPE filament were not uniform across the filament cross section and corresponded well to the obtained velocity profiles. The elongational viscosities of the LDPE filament were relatively higher when the filament was extruded and stretched in the circular die and under the nonisothermal condition. The changes in the elongational viscosity profiles were more sensitive to changes in the volumetric flow rate and roller speed in the circular die. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Polypropylene/polyethylene blends as models for high‐impact propylene‐ethylene copolymers,part 2: Relation between composition and mechanical performance

The relation between composition and mechanical performance of a series of binary polyolefin blends was studied in this article. A fractionation of these model compounds with temperature rising elution fractionation (TREF) was applied to study the possibility to fractionate industrially relevant heterophasic polyolefin systems. The separation quality according to molecular structures or chemical composition was found to be good for most of the systems, but especially the separation of ethylene‐propylene random copolymer and high density polyethylene by TREF turned out to be difficult if not impossible. An extensive mechanical characterisation including the determination of brittle‐to‐ductile transition curves showed significant effects of modifier type and amount. Toughness effects can be related primarily to the modulus differences between modifier and matrix. Compatibility and particle size only have a secondary influence, but must be considered for a detailed interpretation of the mechanics of the investigated systems. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

The role of two different internal donors (phthalate and 1,3‐diether) on the formation of surface structure in MgCl2‐supported Ziegler–Natta catalysts and their catalytic performance of propylene polymerization

The role of two different internal donors [a phthalate (diisobutylphthalate) and a 1,3‐diether (2,2‐diisobutyl‐1,3‐dimethoxypropane)] on the formation of surface structure in MgCl₂‐supported Ziegler–Natta catalysts and their catalytic performance of propylene polymerization was investigated by comparing and correlating the catalyst structures and the polymerization characteristics. In the catalyst formation, the 1,3‐diether had better affinity for the MgCl₂ surface than the phthalate and the 1,3‐diether generated the (110) surface more than the (104) surface while the phthalate generated both the (110) and (104) surfaces of MgCl₂. With both donors introduced, the (110) and (104) surfaces were generated simultaneously, although the (110) surface was dominant due to the higher affinity via the 1,3‐diether. In addition, it seemed probable that the active sites formed on the (110) plane showed isospecific characteristics in the presence of a donor while those formed on the (104) plane could be isospecific regardless of a donor. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40536.     

Influence of some additives on the performance of wood flour/polyolefin composites

The main objective of this study was to investigate the effect of different additives, namely, maleic anhydride, alumina trihydrate (ATH), and a mixture of both on wood flour/polyolefin (50/50) composite samples. The polyolefins used were polyethylene (PE), polypropylene (PP), and a mixture of both PE and PP (50/50 w/w). The effects were studied in terms of the percentage water absorption, volumetric swelling efficiency, and mechanical and electrical properties. We found that the absorption of water and volumetric swelling were greatly retarded after 3 weeks in all of the wood flour/polyolefin composite samples containing various additives. It is also clear from the results that the mechanical properties were enhanced. The presence of ATH improved the electrical properties and enhanced the thermal stability of the wood flour composites. Generally, the PE composite samples gave better results compared to the PP ones. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Effects of neutralization on the structure and properties of an ionomer

The structure, morphology, and properties of an ionomer, poly(ethylene‐acrylic‐acid) neutralized by zinc salts (PI) depend on the free carboxylic acid content. In this work, metal acetates (Na, Zn, and Al acetates) were used to control the neutralization levels. A wide range of techniques were used, such as spectroscopic Fourier transform infrared spectroscopy (FTIR), thermal [thermogravimetric analysis, modulated differential scanning calorimetry (MDSC), and dynamic mechanical analysis (DMA)], mechanical (tensile measurement), and small angle neutron scattering (SANS). The melt rheological properties of the samples were also examined. The results show that metal acetate neutralizes free acrylic acid in the ionomer, which has the primary role in controlling ionic association. The number of ionic groups in ionic domains and multiplets in the matrix is dependent on the neutralization level. Metal valence determines the ionic domain or multiplet structure (FTIR), further properties of PI. Dynamic mechanical properties, the ionic transition behaviour, and the mechanical properties are improved compared with PI using monovalent cation (Na⁺), but decreased using trivalent cation (Al³⁺) or shows less significant changes due to steric effects. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Rheological and thermal properties of polypropylene blends based in a low molecular weight EVA

Blends of polypropylene (PP) and poly(ethylene-co-vinyl acetate) (EVA) having a PP/EVA viscosity ratio of 240 were prepared by melt mixing. EVA concentration varies from 2 to 26 wt%. All blends display two-phase structure with quasi-spherical EVA domains evenly distributed in the PP matrix. The diameter of the domains increases with EVA concentration from about 0.4 to 6 μm. Each component crystallizes separately. The melting temperature of PP phase is no noticeably affected by the presence of EVA while the crystallization one gradually increases by 4°C. The dynamic moduli of the blends are well predicted by the emulsion model of Palierne, revealing that the system PP/EVA has a very small interfacial tension. The thermal degradation behavior of the blends, determined by thermogravimetry, shows that the deacylation process in EVA is not affected by the presence of PP while the beginning of the degradation process of PP is increased by up to 20°C due to the presence of EVA. This effect goes along with an increment in the maximum degradation rate of PP.     

Enhancing mechanical strength of hydrogels via IPN structure

In this investigation, polyacrylamide (PAAm) as the flexible network is introduced to enhance the mechanical strength of hyaluronic acid–gelatin (HA–Gel) hydrogels by interpenetrating polymer network (IPN). The structure, mechanical property, and rheology property of the IPN hydrogels are investigated. It is found that the compressive strength of the HA–Gel/PAAm IPN hydrogels has increased five times higher than that of HA–Gel hydrogels. Rheological test demonstrates that elastic moduli (G′) and viscous moduli (G″) of HA–Gel/PAAm IPN hydrogels increase 100 times higher than those of HA–Gel hydrogels. Moreover, the HA–Gel hydrogels are fractured under the low compressive stress, whereas HA–Gel/PAAm IPN hydrogels are not broken under the high compressive stress. It is envisioned that the IPN hydrogels will be an effective approach to enhance the mechanical strength and broaden the range of hydrogels' applications. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44503.