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Reactive extrusion and high-shear extrusion are both effective methods to regulate the size of dispersed phase and improve the properties for polymer blends, which have been investigated widely but separately. In this work, the combined effect of reactive and high-shear extrusion has been carried out in polylactide (PLA)/olefin block copolymer (OBC)/ethylenemethyl acrylate-glycidyl methacrylate terpolymer (EGMA) blends to better control the phase morphologies and improve the properties. It was found that, for PLA/OBC binary blends (80/20), the size of OBC dispersed phase decreased from 1.95 to 1.09 μm with increasing the rotation speed from 100 to 900 rpm, but the obtained phase morphologies couldn't be maintained after annealing treatment. In contrast, for PLA/EGMA binary blends (80/20), the effect of shear force on the dispersed phase size was negligible, due to the efficient reaction even under relative low shear force, and the morphologies of the annealed specimens is stable. For PLA/OBC/EGMA ternary blends, the suitable dispersed phase size and appropriate interfacial adhesion regulated by variations of composition and shear force lead to a significant increase of impact toughness. Super toughened PLA/OBC/EGMA blend (80/10/10–900) after annealing treatment shows impact strength of 49.61 kJ/m2, 21 times as comparing to that of the pure PLA. Our work demonstrates the importance of a suitable dispersed phase size and appropriate interfacial adhesion for the improvement of impact strength of PLA/OBC/EGMA blends achieved via a combined effect of reactive and high-shear extrusion. Image 1 • The influence of shear force on the dispersed particles size for the blends was systematically investigated. • The effect of dispersed particles size and the interfacial adhesion on the impact strength of the blends was studied. • There was an optimum dispersed particle size for the best toughening effect of amorphous or highly crystalline PLA. • The suitable dispersed particles size and the appropriate interfacial adhesion are necessary for better toughening of PLA. [ABSTRACT FROM AUTHOR]

Abstract Exerting high shear force and adding compatilizer are two different methods used for regulating the size of dispersed phase of polymer blends. Nevertheless, the comparison of the effect of the high shear force and adding compatilizer on the phase morphologyies and properties is less studied, not to mention the synergistic effect. In this work, the incompatible PP/PLA binary blends with large polarity differences were prepared using high-shear processing, compared with the effect of adding ethylene-(methyl acrylate)-(glycidyl methacrylate) (EMA-GMA) as reactive compatibilizer for PP/PLA blends. It was found that adding compatilizer under relative low shear force was more efficient on improving the interface, showing blurred boundaries, compared with the reduction of the dispersed phase size under high shear force without compatilizer. As a result, the blends with the compatilizer presented a higher elongation at break; yet the yield strength of the binary blends prepared under high shear force was higher than that of the ternary blends. Furthermore, the synergistic effect of adding compatibilizer and high shear force was limited, which could be attributed to the fact that the degree of reactive compatibilization had already reached saturation under the rotation speed of 100 rpm due to the high efficiency of EMA-GMA. Graphical abstract Image 1 Highlights • The comparison of the effect of the high shear force and adding compatilizer is systematically studied. • The size of the PLA dispersed droplets decreases significantly under high rotation speed and relatively low temperature. • The PP/PLA binary blends prepared using high-shear processing show higher yield strength and lower toughness. [ABSTRACT FROM AUTHOR]

Melt blending is a promising and practical method to prepare electrical conductive polymer composites containing multiwalled carbon nanotubes (MWCNTs). The key is to achieve a good dispersion of MWCNTs in polymer matrix. In this study, olefin block copolymer (OBC)/MWCNTs composites were prepared using co-rotating twin-screw extruder with high rotation speed and the influence of screw rotation speed on the dispersion, shortening of MWCNTs and the macro-properties of composites was systematically investigated. It was found that the entangled agglomerates of MWCNTs could be easily destroyed by using high rotation speed and an improved dispersion of MWCNTs was observed as increasing of rotation speed from 50 to 500 rpm. However, with further increasing of rotation speed from 500 to 1000 rpm, no better dispersion was evidenced but a reduction of nanotubes length was detected. As a result, the best electrical conductivity and mechanical properties of OBC/MWCNTs composites were achieved via using the rotation speed of 500 rpm. And the electrical percolation threshold obtained was about 1.5 wt%. This study provides significant guidance for large-scale preparation of conductive composites materials by using co-rotating twin-screw extruder with high rotation speed. [ABSTRACT FROM AUTHOR]

Melt mixing and solution mixing are two commonly used methods for the preparation of polymer nanocomposites. In this work, thermoplastic polyurethane (TPU) composites with unmodified MWCNTs and carboxyl MWCNTs (MWCNT-COOH) were prepared using melt mixing and solution mixing. The dispersion of filler in TPU matrix and the macro-properties of composites under different processing conditions were systematically investigated. It was found that for pristine MWCNTs, a better dispersion was obtained using solution method at relatively low content of fillers (≤2.5 wt%); but when the content of MWCNT was above 2.5 wt%, melt mixing under high shear force was more effective to achieve a homogeneous dispersion. The similar result was confirmed in TPU/MWCNT-COOH composites, with the critical concentration shifted to 5.0 wt%, indicating that the interaction between CNT and TPU also played role on the dispersion of CNT in TPU matrix via solution mixing. Our finding is important for the preparation of polymer/CNT nanocomposites with good dispersion depending on the filler content and mixing methods. Image 1052 • The dispersion state of CNT in TPU matrix with solution and melt mixing was compared. • The effect of the concentration and the surface modification of CNT on the dispersion of CNT in TPU matrix was studied. • Melt mixing under high shear force with unmodified MWCNTs is a better way to obtain high-performance composites. [ABSTRACT FROM AUTHOR]

In this study, the crystalline morphology and mechanical property of Olefin Block Copolymer (OBC) were tailored by adding a small amount (up to 10 wt%) of ultrahigh molecular weight polyethylene (UHMWPE). To do this, OBC and UHMWPE was solution blended first and then subjected to compression molding or injection molding, respectively. It was found that a small quantity of UHMWPE (0.5 wt%, 1 wt%) can be fully mixed with OBC, while phase separation occurs when UHMWPE content is higher than 2.5 wt%, as suggested by SEM and DSC results. For compression molded samples, an obvious increase of Young's modulus from 12 MPa to 22 MPa while maintaining the good elasticity of OBC was observed as the content of UHMWPE is less than 2.5 wt% (in the phase miscible range). With further increasing of UHMWPE content to 10 wt%, only slightly increased Young's modulus is seen. Thus the miscibility between OBC and UHMWPE plays an important role in determining the mechanical property for compression molded samples. However, a continuous increase of Young's modulus was observed with the increase of UHMWPE content for samples obtained via injection molding, with a slight increase (from 23 MPa to 40 MPa) as the content of UHMWPE is less than 2.5 wt%, while with a large increase (from 40 MPa to 156 MPa) as the content of UHMWPE increases from 2.5 wt% to 10 wt%, accompanied with a greatly decrease of elongation (from 1100% to 50%). Even elastomer-to-plastic transition takes place when the content of UHMWPE is large (5 wt%, 10 wt%). Structural analysis of injection-molded samples shows that shish-kebab-like structures can be successfully induced as addition of UHMWPE along with gradually increased crystal orientation. It was interesting to find that small-addition of UHMWPE favors increased tie-effect due to the miscibility between OBC and UHMWPE, which is helpful to the elasticity retaining as well as strength enhancement, while large-addition of UHMWPE gives rise to phase separation and mixed shish-kebabs (OBC/UHMWPE hybrid shish-kebabs and UHMWPE homo-shish-kebabs), leading to elastomer-to-plastic transition. [ABSTRACT FROM AUTHOR]

• Low-pressure-oxygen plasma was introduced to the preparation of conductive foams. • Skeleton of plasma-treated foams have better affinity with conductive layer. • The as-prepared foams exhibit excellent compressive sensitivity and durability. Rapid development of artificial intelligence and wearable electronics facilitate the demand for high performance piezoresistive sensors. Not only high sensitivity but also good mechanical property as well as long-term usage are critical parameters to value piezoresistive sensors performance. In this work, a flexible, highly sensitive and versatile piezoresistive sensor with 3D porous structures, based on commercially available polyurethane (PU) foams coated with cellulose nanofiber @ carbon black (CNF@CB) conductive layer, was fabricated. We are particularly interested in the effect of interaction between the conductive filler and PU foam on the sensor performance. Thus, low-pressure oxygen plasma treatment was innovatively adopted to modify and activate PU scaffold to enhance the affinity between PU framework and CNF@CB conductive layer. Strong interfacial interaction is not only contributed to the sensitivity but also to the mechanical reinforcement of conductive foams, which is helpful to the long-term usage. The as-prepared PU/CNF@CB conductive foams exhibit very high compressive sensitivity of 0.35 kPa−1 (about 100% increase compared with the untreated ones), along with good mechanical property (29 kPa at 50% compressive strain, about 27% increase compared with the untreated ones) and electrical property (0.047 S/m). In addition, good stability and durability are demonstrated for the prepared PU/CNF@CB conductive foams especially under micro-pressure or micro-strain which is a huge challenge for bulk piezoresistive sensors. Such a kind of sensitive material combined with low-cost, flexibility, high sensitivity, duration, is very attractive in high-tech area. [ABSTRACT FROM AUTHOR]

Recently, stereocomplex-type polylactide (SC-PLA) has generated growing interest because the unique SC crystals can provide drastic improvement in the heat/chemical resistances and durability of bio-derived and biodegradable PLA, exhibiting great potential to compete with some petroleum-derived engineering plastics in diverse applications. However, SC-PLA suffers from poor melt memory effect as well as significant thermal degradation after being completely melted at temperatures above 250 °C, which make it challenging to converse SC-PLA into useful products using versatile melt-processing technologies. With these challenges in mind, in this work, we propose a facile and practical strategy to fabricate SC-PLA products with exceptional thermomechanical properties through low-temperature melt-processing of SC-PLA powder with a bimodal melting temperature distribution. The results show that the melting temperature (T m) bimodality makes SC-PLA powder able to be easily injection molded at a relatively low temperature of 210 °C (between the two T m s) due to the selective melting of the low- T m SC-PLA component (SC- l PLA, ca. 20–40 wt%), indicating a good melt-processability. Meanwhile, the high- T m SC-PLA (SC- h PLA) component can directly deliver its desirable properties to the injection molded SC-PLA products. More importantly, during the injection molding process, the unmelted SC- h PLA particles can also induce the exclusive SC crystallization of the SC- l PLA melt as nucleating agent and greatly amplify the shear stress imposed on the melt as "rigid particles", finally generating numerous oriented SC structure in the SC- l PLA. Consequently, the injection molded SC- h PLA/SC- l PLA products exhibit impressively high tensile strength (74.3 MPa) and Vicat softening temperature (211.6 °C). Overall, this work presents an effective guidance for achieving desirable melt-processability of SC-PLA without sacrificing its thermomechanical properties and provides an industrial processing route towards high-performance SC-PLA products. Image 106841 • SC-PLA products were fabricated by low-temperature melt-processing of bimodal SC-PLA powder. • The melting temperature bimodality plays a key role in achieving balanced melt-processability and product performance. • The SC- l PLA component can provide the powder with good low-temperature melt-processability. • The SC- h PLA component can endow the melt-processed products with exceptional thermomechanical performance. • SC- h PLA induced exclusive SC formation and crystal orientation can also contribute to the enhanced performance. [ABSTRACT FROM AUTHOR]

Herein, we reported the formation mechanism of hybrid crystalline (cylindrite) in isotactic polypropylene (iPP)/carbon fiber (CF) via pulling a CF within the iPP melt. The α‐row nuclei layer closely attached to the surface of CF acts as a self‐nucleation site, rather than a heterogeneous nucleation one, to grow cylindrites. As a result, the polymorphic feature of iPP/CF cylindrite is significantly influenced by the microstructure of α‐row nuclei. With decreasing crystallization temperature (Tc), the polymorphic cylindrite changes from pure α‐form to mixed α‐/β‐form and to β‐rich form. The main characteristics of this change include: (a) the outlines of α‐row nuclei layer correspond to wave‐like, saw‐like, and straight lines; (b) the orientation level of iPP molecules in the α‐row nuclei layer become higher; (c) the α‐lamellae rearrange from loose to compact; and (d) the distance between the growth sites of β‐sectors and the surface of CF is evidently longer than in the case of α‐sectors. Moreover, this study provides a guideline for developing the interfacial enhanced iPP/CF composites through manipulation of polymorphic structure in cylindrites. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019, 57, 368–377 The correlation between the α‐row nuclei and shear‐induced iPP/CF variable cylindrite (pure α‐cylindrite, mixed α/β‐cylindrite, and β‐rich cylindrite) was systematically established by comparing the detailed microstructure. The systematical growth processes of shear‐induced cylindrites with different crystalline temperatures are illustrated. Furthermore, it was concluded that the polymorphism of cylindrite is strongly dependent on the orientation and packing density of the fibril lamellae in the α‐row nuclei. [ABSTRACT FROM AUTHOR]