In recent years, rubber toughened polypropylene (PP) blends have been extensively investigated with special regard to the importance of PP matrix properties (e.g., crystal morphology and structure) ...in tailoring the toughening efficiency. Unfortunately, although high melt flowability is indispensable to the processing of polymers into complex thin-wall products, it remains a huge challenge to achieve a marvelous balance between stiffness and toughness in the blends with relatively low matrix molecular weight. Herein, taking PP/EPR (ethylene-propylene copolymer) blends as an example, the combined effects of matrix molecular weight and crystallinity on the mechanical properties of PP/EPR blends have been examined in both experiment and theory. The experimental results show that decreasing molecular weight leads to significant deterioration in notched impact toughness, tensile strength and Young's modulus. Impressively, the toughness loss caused by the decrease of molecular weight can be well-compensated by a slight reduction in the matrix crystallinity, without evidently sacrificing the strength and modulus, demonstrating an improved stiffness-toughness balance. Theoretical analysis indicates that the impact toughness of PP/EPR blends is heavily dependent on the chain entanglement density (ve) of PP matrix, and a linear relationship between critical interparticle distance (IDc) and the ve1/3 has been verified from both experiment and theory. Moreover, it is interesting to find that decreasing matrix crystallinity can increase the ve of low-molecular-weight PP matrix, which enables the effective toughening at lower concentration of EPR and thus gives rise to less loss in the strength and modulus. We believe this work not only gives a new insight into the role of chain entanglement in the toughening but also provides a promising guidance for the design of high-performance PP with high melt flowability.
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•Combined effects of Mn and crystallinity on the toughening efficiency of PP/EPR blends were studded.•The relationship between the IDc and ve of PP matrix i.e. IDc ∼ ve1/3, was given for the first time.•Matrix with higher Mn or lower crystallinity has higher ve, exhibiting larger IDc.•Toughness loss caused by decreasing Mn can be compensated by reducing crystallinity.•Low-viscosity PP/EPR blends with good toughness-stiffness balance were obtained.
Tofu quality is determined by a controlled coagulation process using a W/O/W emulsion coagulant. The impact of adding soy protein isolate (SPI) to the inner water phase on the stability of W/O/W ...high-internal-phase emulsions (HIPEs) and its application as a coagulant for tofu was assessed. No creaming occurred during 7-day storage with SPI concentrations up to 0.3%, while the emulsion droplets aggregated with 0.5% and 0.7% SPI. Emulsions containing 0.3% SPI maintained a constant mean droplet size after 21 days of storage and exhibited the lowest TURBISCAN stability index value. HIPE stability against freeze–thaw cycles improved after heating. HIPEs with SPI concentrations above 0.3% demonstrated an elastic gel-like behavior. The increased viscosity and aggregation of the protein around droplets indicated that the interaction among emulsion droplets could enhance stability. W/O/W HIPE coagulants significantly increased tofu yield, reduced hardness, and produced a more homogenous tofu gel compared to a MgCl2 solution. The HIPE with 0.3% SPI was found to be optimal for use as a coagulant for tofu.
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•The complexes of whey protein fibrils-sodium alginate (WPIFs-SA) were prepared.•The stability of Pickering emulsions was increased by WPIFs-SA complexes.•WPIFs-SA based Pickering ...emulsion protected lycopene from UV and heat degradation.•Increased oil fractions or complexes contents delayed lycopene and Free Fatty Acid (FFAs) release during digestion.
In present study, whey protein isolate fibrils and sodium alginate complexes (WPIFs-SA) were prepared and further used to stabilize Pickering emulsions for lycopene delivery. The optimal interaction between WPIFs and SA occurred at pH 3.0, with a mass ratio of 2:1. Increasing the oil fractions and the content of WPIFs-SA complexes significantly improved Pickering emulsions’ stability, concurrently reducing droplet size and increasing viscoelasticity. Meanwhile, it facilitated the formation of a thicker protective layer and a compact network structure around the oil droplets, offering better protection for lycopene against thermal and photo degradation. In vitro digestion studies revealed that as the oil fractions and complex contents increased, the lipolysis degree decreased. The engineered WPIFs-SA Pickering emulsion could be used as an innovative delivery system for the protection and delivery of lycopene.
This paper proposes a new framework of defining an overall constitutive model of the fibrous composite material with separated constitutive models of the fiber and the matrix phases. The framework ...stems from the first-order reduced-order-homogenization (ROH) method. The ROH method requires a set of influence functions to describe the interaction between material phases, which can be computed by solving a number of finite element problems of the fibrous meso-structure with periodic boundary conditions. This paper proposes an analytical methodology to evaluate the influence tensors. In this way, the overall constitutive model of the fibrous composite material is constructed by analytical influence tensors and stand-alone material models of the fiber and matrix phases, which can represent comprehensive material degradation mechanism at meso-scale. Finally, an example of overall constitutive model is defined and tested, with both fiber and matrix phases are assumed as the isotropic continuum damage model.
The PBAT/PGA blend film, composed of poly(butylene adipate-co-terephthalate) and poly(glycolic acid), is currently considered promising, cost-effective, and comprehensively performing biodegradable ...mulch film. However, the relatively fast hydrolysis rate limits its service time during application. This work endeavored to postpone the hydrolysis rate of the PBAT/PGA blend films by using polycarbodiimide (PCDI) as an antihydrolysis agent. Through artificial accelerated weathering experiments, thorough analysis of the microstructure, surface morphology, thermal properties, and mechanical properties, of the blend films was conducted. Moreover, the antihydrolysis mechanism was clearly revealed. Results showed that the introduction of PCDI enhanced the durability and overall performance of PBAT/PGA blend films. PCDI not only consumed the carboxyl-end groups of polymer molecular chains but also acted as a chain extender. In summary, the enhanced hydrolysis stability and excellent mechanical properties endow the PBAT/PGA blend films with significant developmental potential for mulch films with a stable service life and superior performance.
•Additives affect recrystallization from the melt of commercial linear low density polyethylenes (LLDPE).•Additives are consumed after melt-reprocessing and the effect of melt-memory or ...self-nucleation on recrystallization can be followed by DSC.•The effect of melt-memory on recrystallization of LDPEs and metallocene LLDPEs differs from the behavior of broadly distributed Ziegler-Natta LLDPEs.•Studying the effect of melt-memory on recrystallization of LLDPEs by DSC is a simple avenue to identify if LLDPEs undergo liquid-liquid phase separation (LLPS) on cooling from the melt.
Compared with a constant recrystallization rate of commercial linear low density polyethylenes (LLDPE) as a function of melt temperature, copolymers reprocessed in an open twin-screw extruder, display the expected strong melt-memory features upon melting followed by recrystallization. Precipitation from dilute solution had the same effect on melting-recrystallization of commercial copolymers. In the twin-screw melt re-processing, a small content of long-chain branches and crosslinks are incorporated to the copolymer's structure, but especially a further consumption of additives uncovers self-nucleation features that speed up recrystallization and are related to the major copolymer microstructure. The observed difference in re-crystallization behavior between metallocene type and Ziegler-Natta (ZN) type copolymers, both with equivalent average comonomer content and molecular mass, is due to the inter-chain comonomer distribution. While for metallocene-made and low density polyethylenes, below a critical melt temperature the recrystallization rate increases continuously with decreasing melt temperature, in broadly distributed ZN copolymers there is an inversion of the temperature gradient of the rate at the onset of liquid-liquid phase separation (LLPS). The mass fraction of highly branched molecules required to observe the onset of LLPS via melting followed by recrystallization was evaluated from the TREF profiles, and the effect of self-nucleated melts at different levels on the overall spherulitic morphology was observed via polarized optical microscopy.
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When konjac glucomannan (KGM) molecules are deacetylated under alkaline conditions, the aqueous KGM solution is transformed into a thermally stable gel. In this study, series of Na2CO3-induced and ...K2CO3-induced KGM hydrogels were prepared by deacetylation using different concentrations (0.1, 0.2, 0.3, and 0.4 M) of alkali. The hydrogels were characterized using texture profile analysis, scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy, X-ray diffraction, and rheological property analysis. The data showed that KGM hydrogel formation was facilitated at all the alkali concentrations used. The mechanisms of Na2CO3-induced and K2CO3–induced KGM hydrogels formation differed slightly. The hardness, springiness, chewiness, gumminess, and storage modulus G′ of the Na2CO3-induced KGM hydrogels initially increased and then decreased with increasing alkali concentration. However, the values of the corresponding properties of the K2CO3-induced KGM hydrogels increased with increasing alkali concentration. All the data were consistent with the structures observed using SEM. The 0.3 M Na2CO3-induced KGM hydrogel had the highest hardness and storage modulus G′, a well-proportioned network structure, and a dense architecture; 0.3 M Na2CO3 was therefore the most suitable modifier for inducing KGM hydrogel formation.
•Na2CO3-induced KGM hydrogels and K2CO3-induced KGM hydrogels were prepared.•The mechanisms of KGM formation induced by Na2CO3 and K2CO3 differed slightly.•0.3 M Na2CO3 was the most suitable modifier for inducing KGM hydrogel formation.
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•The SP-COPs exhibited high catalytic efficiency of CO2 conversion and excellent I2 adsorption capacity.•The synergistic mechanism of CO2 conversion was proved by experimental and ...kinetics.•The iodine adsorption kinetic process was described.
The fixing reactions of carbon dioxide with epoxides will not only help to ameliorate the problem of global warming, but also facilitate the synthesis of cyclic carbonates that have a multitude of applications. Herein, a new sequence of Salen cobalt complexes adjusted with different counterions and interconnected with pyrene group were synthesized through Friedel–Crafts alkylation, which were served as conjugated organic polymers (SP-COPs) for taking advantage of catalytic CO2 fixation reactions and iodine adsorption. Further characterizations were carried out through FT-IR, UV, TGA, and SEM to comprehend the intact structure, thermal stability, morphology and other physical and chemical properties. All materials exhibited effective catalytic performance, and in particular, SP-COP-1 with co-catalyst of TBAI achieved 96.2% conversion under ultra-mild conditions. The Ea was obtained to be 46.4 kJ·mol−1 by performing kinetic experiments at different temperatures by fitting the experimental data. The performance of iodine vapor adsorbed by these materials at ambient pressure of 75°C reached 2.8 g·g−1, 2.2 g·g−1 and 2.6 g·g−1 respectively, and the adsorption process is describable in terms of pseudo-first-order and pseudo-second-order adsorption kinetics.
The orientation of the dispersed phase and crystals in the injection-molded bar of an impact polypropylene copolymer (IPC) containing isotactic polypropylene (iPP), ethylene-propylene rubber (EPR) ...and a β-nucleating agent (β-NA) were studied simultaneously. In the IPC, iPP and EPR act as the matrix and dispersed phase, respectively. The EPR is amorphous and the iPP is crystallizable in α- and β-crystalline forms in the presence of the β-NA. The orientation and orientation distribution for both of the EPR phase and the iPP crystals, as well as the crystallization behavior of iPP, were investigated by two-dimensional wide-angle X-ray diffraction (2D-WAXD), two-dimensional small-angle X-ray scattering (2D-SAXS), scanning electron microscope (SEM) and differential scanning calorimetry (DSC). The results of the experiment show that orientation exists for both the EPR phase and the iPP crystals. But their orientation distribution manifests an opposite tendency. The EPR phase was observed to be highly oriented in the core layer but the orientation of the iPP crystals was weakened gradually from skin to core. The difference in the orientation behavior between the EPR phase and the iPP crystals reflects the distinct response of the micrometer-scale EPR particles and nanometer-scale iPP chains upon the flow field and temperature gradient in the mold. The diffraction geometry of the β-crystals has also been discussed in detail. The observations in this study may shed light on the study in the structure and property relationship for the IPC injection-molded products.
•The orientation of the rubber phase and polypropylene crystals were studied simultaneously in an impact propylene copolymer (IPC).•Morphology, calorimetry, and X-ray methods were applied.•The rubber particles and polypropylene crystals were oriented differently.•The orientation of the polypropylene in the presence of the β-nucleating agent was analyzed.•The findings are important for the research and application of IPC.
