Polyolefin blends
Somayeh Rafiei; Davood Soudbar; Minoo Sadri; Fatemeh Shafiei
Abstract
Thermoplastic vulcanizates (TPVs) were prepared based on polypropylene (PP) and polybutadiene rubber (PBR) at different PP/PBR compositions (70/30 and 60/40). PP-grafted-maleic anhydride (PP-g-MA) was introduced into the TPVs at different concentrations (10 and 20%). The compatibilizing effect of PP-g-MA ...
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Thermoplastic vulcanizates (TPVs) were prepared based on polypropylene (PP) and polybutadiene rubber (PBR) at different PP/PBR compositions (70/30 and 60/40). PP-grafted-maleic anhydride (PP-g-MA) was introduced into the TPVs at different concentrations (10 and 20%). The compatibilizing effect of PP-g-MA was demonstrated through cross-sectional morphology. PP-g-MA exhibited a suppressing impact on the coalescence of the rubber domains, leading to a finer and more uniform distribution of the PBR phase. Due to the higher rubber content, the compatibilizing effect was more pronounced for the 60/40 composition, which was on the averge of forming a co-continuous morphology. However, it was found that a higher PP-g-MA content is needed to effectively compatibilize the TPVs. Rheological results revealed opposing effects on the viscoelastic response of the system. However, the elastic response was intensified once higher content of PP-g-MA was used, suggesting its compatibilizing role. Dynamic mechanical analysis results proved the existence of opposing effects and revealed the profound compatibilizing effects of PP-g-MA, especially at higher content (20%). Izod impact strength exhibited moderate and notable enhancements in both TPV compositions by adding 10% and 20% of PP-g-MA, respectively, attributed to the highly increased compatibility of the PP/PBR TPVs, especially at higher levels of PP-g-MA content.
Characterization
Ahmed Hamdi
Abstract
Describing the solidification process is very important in polymer processing. In polypropylene (PP), the increase of viscosity, named stiffening or hardening, is determined by a rise in crystallinity. When PP flows in a channel or is stretched on a chill roll, the stress induces an anticipated crystallization ...
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Describing the solidification process is very important in polymer processing. In polypropylene (PP), the increase of viscosity, named stiffening or hardening, is determined by a rise in crystallinity. When PP flows in a channel or is stretched on a chill roll, the stress induces an anticipated crystallization and thus can lead to an unexpected solidification. This study explores how flow fields influence the crystallization behavior of PP. A controlled-stress rheometer was used to investigate the effect of short shear stress steps on crystallization kinetics. The results revealed that applying a stress step significantly increased the rate of crystallization compared to a non-stressed sample. This acceleration is attributed to the stress-induced orientation of macromolecules, which promotes nucleation. Furthermore, longer durations of applied stress led to a faster increase in viscosity, indicating a higher nucleation density with increasing stress exposure. A mastercurve approach validated the consistency of the model describing the stress-crystallization relationship. The calculated parameter relating to nucleation density confirmed a linear increase with stress duration, allowing estimation of the nucleation rate during shear.
Simulation & Modeling
Aamir Mustafa Shaikh; Pravin R. Kubade
Abstract
Polymers can be natural or synthetic and are largely used in several applications due to their versatile properties. Polymers can vary widely in their properties and applications, and they are a fundamental part of our everyday life. Polypropylene (PP) is a thermoplastic polymer from the polyolefin family. ...
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Polymers can be natural or synthetic and are largely used in several applications due to their versatile properties. Polymers can vary widely in their properties and applications, and they are a fundamental part of our everyday life. Polypropylene (PP) is a thermoplastic polymer from the polyolefin family. It is among the most widely used plastics in various automotive and packaging industries. Although PP is widely used in commodity range, still its applications are restricted in niche areas due to lack of toughness which can be improved by incorporation of rubbery materials or fillers. Graphene (G) is one of the nanomaterials used to strengthen polypropylene. Graphene is recognized for its outstanding thermo-mechanical properties, making it a highly desirable material in various fields of science and technology. Benefits gained by incorporation of graphene nanoparticles into polypropylene are studied by researchers. In this study, a finite element analysis is performed which shows the mechanical behaviour of PP and G using ANSYS, which is one of the most powerful finite element analysis (FEA) softwares that can help to perform such simulations to understand stress, strain, deformation of components before actual experimentation. The bending load of 100 N and 1400 N in vertical z-direction are applied for 100% PP model, 100% G model and 50% PP+50% G model and the linear part of stress-strain curve is captured in this analysis.
Computational chemistry & molecular modeling
Fan Zhang; Jieqi Wang; Yangyang Zhao; Xuelian He
Abstract
The effect of long chain content (XL ) on the static crystallization and tensile deformation mechanisms of bimodal HDPE/UHMWPE was investigated by molecular dynamics simulations. The crystallization of HDPE/ UHMWPE undergoes three stages: nucleation, rapid growth of lamellar crystals, and stabilization. ...
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The effect of long chain content (XL ) on the static crystallization and tensile deformation mechanisms of bimodal HDPE/UHMWPE was investigated by molecular dynamics simulations. The crystallization of HDPE/ UHMWPE undergoes three stages: nucleation, rapid growth of lamellar crystals, and stabilization. The increase of XL leads to the formation of more nucleation sites, which promotes nucleation, but at the same time leads to an increase of entanglement sites, which is not conducive to the movement of the long chains to the growth front to fold and form lamellar crystals. Tensile deformation is performed on the crystallized models and the systems exhibit three stages: elastic deformation, plastic deformation and stress hardening. During deformation, the increase of XL improves the orientation nucleation and crystallinity (Xc), but when XL exceeds 4 wt.%, the entanglement effect becomes more pronounced, leading to a decrease in Xc. The effect of temperature is also taken into account: at low temperatures, a suitable range (2-4 wt.%) exists to optimize the mechanical properties of the material. At high temperatures, there is almost no stress-hardening phenomenon, but the addition of long chains has an impeding effect on the melting of the lamellar crystals, and when XL is greater than 8 wt.%, stress-induced melting is more likely to occur, accelerating the melting of the crystals.
Structure and property relationship
Zhijie Zhao; Ping Hai; Minjuan Zhang; Yongbiao Zheng; Yuerong Chen; Cunling Long; Hongtao Zhang; Xinyi Zhang
Abstract
The presence of ultrahigh molecular weight species in polymer melt facilitates the formation of highly-oriented crystalline structures and favors the improvement of mechanical properties. However, due to the random copolymer chain architecture, it is difficult to obtain high orientation of crystals for ...
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The presence of ultrahigh molecular weight species in polymer melt facilitates the formation of highly-oriented crystalline structures and favors the improvement of mechanical properties. However, due to the random copolymer chain architecture, it is difficult to obtain high orientation of crystals for polypropylene random copolymers (PPR). In this work, two binary blends including polypropylene (PP)/ultrahigh molecular weight polyethylene (UHMWPE) and polypropylene random copolymer (PPR)/UHMWPE were fabricated via solution blending and subsequent melt shear through mini-injection molding. It was found that a highly-oriented crystalline structure forms under shear flow in both blend series. The tensile strength of PP blends increased from 38.3MPa to 43.8MPa while the PPR blends showed a more significant property enhancement and increased from 32.5MPa to 38.1MPa. Importantly, PPR showed an increased miscibility with UHMWPE in comparison with PP due to the existence of ethylene segments. The tensile toughness of PPR samples was greatly maintained especially for blends with small addition of UHMWPE, which may be ascribed to the crack-suppression effect originated from well[1]dispersed UHMWPE domains (particle size < 0.50 μm) locked by the cocrystal structures between PPR segments and molecularly mixed PE chains.
Composites and nanocomposites
Shahryar Malekie; Mohammad Amin Hosseini; Ahmadreza Abiz; Fatemeh Bolourinovin; Suffian Mohamad Tajudin
Abstract
This research aims to determine and quantify the radiation shielding characteristics of High Density Polyethylene/Tungsten Oxide composite (HDPE/WO3) including the linear attenuation coefficient (µ), mass attenuation coefficient (µ/ρ), half-value layer (HVL) and tenth-value layer (TVL) ...
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This research aims to determine and quantify the radiation shielding characteristics of High Density Polyethylene/Tungsten Oxide composite (HDPE/WO3) including the linear attenuation coefficient (µ), mass attenuation coefficient (µ/ρ), half-value layer (HVL) and tenth-value layer (TVL) for photons at various energies using Geant4, XCOM, and experiment. Thus, HDPE was chosen as the polymer matrix. Then, the samples at various concentrations of WO3 nanoparticles, including 0, 1, 2, 3, 4, 5, 6, and 9.5 wt%, different graphene oxide (GO) wt% namely 0, 0.25, 0.5, and 1 wt%, and linear low-density polyethylene (LLDPE) at 10, and 20 wt% were fabricated. NaI (Tl) scintillation detector was used to measure the shielding quantities using the 201Tl, and 99mTc sources at three energies of 135, 140, and 167 keV. The experimental results demonstrated that the addition of GO and LLDPE to the HDPE matrix resulted in a more uniform samples. Incorporating 20% LLDPE into the HDPE polymer matrix for the 99mTc resulted in an 18% rise in µ compared to pure HDPE. Finally, experimental results revealed a comparatively good agreement with the Geant4 and XCOM simulations.
