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Shear relaxation behavior for polymer melt exists in different processing techniques and influences the dimensional accuracy and production efficiency of polymer products. A micro physical and mathematical model based on microstructure of polymer chains and processing parameters was established and verified by experimental results obtained from a torque rheometer. The shear relaxation time of polypropylene degraded by di tert-butyl peroxide was characterized with torque rheometer. The effects of microstructure and processing parameters on the shear relaxation time was investigated. The results showed that a wider molecular weight distribution could result in a decrease in shear relaxation time and polypropylene chains with higher molecular weight were more sensitive to molecular weight distribution. The shear relaxation time declined exponentially with shear rate and increased with internal pressure. The temperature could enhance the movement of polymer chains and reduce the shear relaxation time linearly, but polypropylene with lower molecular weight was less sensitive to temperature. The insight obtained from the mathematical and experimental results can be profoundly applied in practical process control to manufacture product with better dimensional stability and production efficiency for viscoolastic polymer. Highlights * A physical and mathematical model based on microstmcture and processing parameters of molecular chains was established to explore the shear relaxation mechanism. * Shear relaxation time of polypropylene degraded by di-tert-butyl peroxide was characterized with the help of torque rheometer. * The effects of microstmcture and processing parameters on shear relaxation time was investigated to optimize the manufacturing of polypropylene products. KEYWORDS molding, molecular weight, polymer melt, shear relaxation, shear stress decay, 1 | INTRODUCTION Polymer and polymer composites were widely used in civil and industrial applications for its excellent mechanical performance and easy to process characteristics. The relaxation behavior takes an [...]

Research on the preparation of starch-based degradable foams by adding simple raw materials and using simple processes meets the requirements of modern society and market demand. Water is the most common raw material in daily life, its triple transformation is easy to achieve, and it has an important effect on many aspects of the starch foaming process. This paper presents the research results on the preparation of starch-based foaming materials using water as an important raw material, summarizing the mechanism of the action of solid-liquid gaseous water in the plasticization, foaming, hydrophobic, and swelling processes. Water vapor fumigation of starch materials uses high temperatures to induce the inversion (or dehydration) of the hydroxyl groups distributed on the surface, reducing the water sensitivity of the starch foam surface. Finally, the development trend is analyzed and foreseen, in order to provide new ideas for the development of low-cost methods to prepare degradable and environmentally friendly packaging materials. KEYWORDS foaming, hydrophobicity, plasticizing, starch, water, 1 | INTRODUCTION Traditional foam plastic has the advantages of light weight, good cushioning, good heat and sound insulation, etc., and is an essential part of the modern packaging industry. [...]

Polylactic acid (PLA) is one of the most widely used biodegradable materials at present due to its excellent reproducibility and degradability. However, PLA still suffers from poor crystallinity, which seriously affects its development and application. Therefore, PLA/cellulose nanocrystalline (CNC)‐polyethylene glycol (PEG) composite (PLA/CNC‐PEG) was prepared by melt blending using CNC as nucleating agent and PEG as compatibilizer. The effect of PEG with different molecular weights (MW) on the properties of PLA/CNC‐PEG composite was investigated. The experimental results shown that the crystallization properties of PLA were greatly improved under the synthetic action of CNC and PEG. With the increasing MW from 400 to 20,000 of PEG, the crystallinity of PLA/CNC‐PEG composite decreased from 32.1% to 13.3%. In addition, the crystallization model of PLA/CNC‐PEG was constructed to explore the mechanism of crystallization growth of PLA, effectively guiding the reduction of crystallization activation energy of PLA. Furthermore, it was found that PLA/CNC‐PEG exhibited good thermal stability, mechanical properties, and hydrophilicity with the addition of CNC and PEG400. Therefore, the synthetic action of CNC and PEG well regulated the performance of PLA. The proposed work is of hopeful to expand the application of PLA in production and life. [ABSTRACT FROM AUTHOR]

Nanozymes, as artificial enzymes, overcome the low catalytic efficiency, poor stability, and cost-effectiveness of previous artificial enzymes. In this work, vanadium carbide@vanadium oxide (V2C@VOx) nanosheets were synthesized by a one-pot hydrothermal method using V2C as a precursor and H2O2 as an oxidant. The prepared V2C@VOx nanosheets exhibited excellent multi-enzyme activity such as peroxidase-like activity, superoxide dismutase-like activity, and oxidase-like activity. The entire synthetic process of V2C@VOx nanosheets does not need any additional intercalation agent, strong acid, or base. Meanwhile, the synthesized method of nanozymes was simple, time-saving, and environmentally friendly. In particular, based on the multi-enzyme activity of V2C@VOx nanosheets, the nanozymes catalyzed H2O2 and dissolved O2 to oxidize 3′,3,5,5′-tetramethylbenzidine (TMB). Additionally, glucose reacted with glucose oxidase (GOx) to form H2O2 under water bath conditions. Therefore, the colorimetric sensing strategy of glucose was constructed based on the multi-enzyme activity of V2C@VOx nanosheets and the enzymatic reaction of glucose. The detection limit of the sensor was as low as 0.08 μM. Furthermore, the colorimetric method was successfully used to detect glucose in human serum. The sensor exhibited low cost, high stability, and easy construction. Overall, this work proposed a promising strategy based on novel vanadium-based nanozymes with excellent multi-enzyme activity for biomedical detection. [ABSTRACT FROM AUTHOR]

In this work, the functional polylactic acid (PLA) was synthesized using epoxy chain extender (ADR) as a chain extender agent through melt blending method. The effects of ADR content on the molecular structure, thermal properties, and tensile properties of the functional PLA were investigated. Meanwhile, the hydrolytic behavior of the PLA/ADR materials at different hydrolysis temperatures was explored. It was found that ADR effectively regulated the molecular structure of PLA in the molten state and significantly increased the relative molecular weight, storage modulus, and complex viscosity of PLA. In addition, the Cole‐Cole diagram results suggested the branched structure of PLA chain expansion systems. Based on mechanical property tests, it was noted that the addition of ADR made the molecular chain form a micro‐crosslinked structure. Additionally, the mass loss rate of PLA/1.6ADR (the dosage of ADR was 1.6 wt%) was 14.75% after 14 weeks of hydrolysis under hydrolysis conditions at 58°C, while that of pure PLA was 25.89%. Moreover, the functional PLA/ADR materials exhibited significantly slower decrease rates in molecular weight, melting temperature, and tensile strength, and still maintained intact morphology after 14 weeks of hydrolysis compared to pure PLA. Therefore, the molecular structure of PLA is effectively regulated by ADR, which greatly enhances the hydrolysis resistance and further promotes the range of application of PLA. [ABSTRACT FROM AUTHOR]

In this work, a novel functional polylactic acid (PLA) was prepared by melt blending using epoxy Joncryl ADR 4468 (ADR) as chain extender. The effects of the epoxy chain expander ADR on the molecular structure, crystallization properties, rheological properties, and mechanical properties of PLA were studied. Furthermore, the chain expansion mechanism was analyzed. It was found that the epoxy group of the epoxy chain extender reacted with the terminal hydroxyl and terminal carboxyl groups of PLA in the molten state, thus significantly increasing the molecular weight of PLA. Meanwhile, the weight average molecular weight of PLA increased by 42.51% when the maximum additional amount of epoxy chain extender was 1.2 wt%. The dynamic rheological experiments also confirmed that ADR can effectively improve the storage modulus, loss modulus and complex viscosity of PLA systems and the Cole‐Cole diagram reveals the branched structure of PLA chain expansion systems. The formation of this branched structure will destroy the regularity of the PLA chain, reduce the crystallization capacity of PLA, and increase the cold crystallization temperature of the PLA system. Through SEM and mechanical property tests, it is found that the addition of ADR makes the molecular chain form a micro‐crosslinked structure, thereby improving the tensile strength of PLA. Therefore, the molecular structure of PLA was effectively regulated and exhibited a promising performance, which greatly expands the potential applications of PLA. [ABSTRACT FROM AUTHOR]

Suspensions of SiO2 microspheres in glycerine exhibit drastic shear-thickening behavior under steady shear and dynamic oscillatory shear test. The rheological behavior of suspensions agrees with the modified Cox-Merz rules as the dynamic oscillatory rheological behavior at low frequency could be reasonably interpreted in terms of the steady shear behavior. As new insight, the effect of shear history and the relaxation on the rheological behavior was investigated in detail. The result showed that under continuous shear, the viscosity decreases after a “pulse”: The degree of decrease is directly proportional to the shear rate. Similar phenomenon is also found under the continuous stress and dynamic oscillatory shear rate sweep. The shear history shows a non-negligent effect on the rheological behavior, the suspensions with higher viscosity show a lower viscosity under the same shear rate. Moreover, the relaxation time of suspensions shows the direct dependency on the initial viscosity, while the volume fraction of suspensions also affect the relaxation time. For more enlapsed times, also longer relaxation times are needed for the suspensions with lower volume fraction and higher initial viscosity.

For developing a new composite material owning shear-thickening characteristic, the rheological behaviors of nano-sized precipitated calcium carbonate (PCC) particles with irregular sharp in glycerine were investigated systematically by means of steady and dynamic rheometry. The results showed that the concentrated PCC suspensions exhibit a strong shear-thickening behavior under both steady and dynamic oscillatory shear when the volume fraction of PCC above the threshold (about 41%). In steady shear tests, the critical shear rate decreases and the maximum viscosity in shear thickening region increases dy namically with the increase of volume fraction. While, for suspensions with different volume fractions, the similar critical stress for the onset of shear thickening is found. In dynamic strain sweep at different fixed frequencies, with the increase of fixed frequency, the complex viscosity of suspensions decreases slightly, while the critical strain for shear-thickening shifts to lower value. The dynamic oscillatory rheological behavior of suspensions at low frequency (ω < 100 rad/s) could be reasonably interpreted in terms of the steady shear behavior. For the suspensions with same volume fraction, it was interestingly found that the critical dynamic shear rate equaled to the product of critical strain and frequency could agree well with the critical shear rate in steady shear. Moreover, the rheological behavior of PCC suspensions shows excellent reversibility and reproducibility.

Recent years have witnessed growing research interest in applying rheology in grinding and flotation treatment of finely disseminated ores. Slurry rheology has long been identified as the comprehensive effect of inter-particle interactions, including their aggregation and dispersion states in slurry, which are more impactive under the fine-particle effect. In this regard, rheology has the potential to play a significant role in interpreting the flowing and deforming phenomena of inter-particle aggregates, particle-bubble aggregates, and flotation froth. Though much attention has been paid to the rheological effect in industrial suspension, this has not been the case for mineral grinding and flotation for fine particles. The influential mechanism of rheology on the sub-processes of mineral processing has not been systemically determined nor revealed thoroughly, thus the underpinning mechanism for enhancing the processing efficiency has been difficult to discover. This paper reviews the current application and importance of rheology in fine mineral processing, and the potential research direction in the field is proposed. [ABSTRACT FROM AUTHOR]