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As a popular "green" engineering plastic, stereocomplex-type polylactide (SC-PLA) exhibits great application potential in various fields owing to its outstanding physicochemical performance and durability. However, the applications of SC-PLA still face formidable challenges mostly associated with its inferior melt-processability (i.e., the weak melt memory effect to motivate exclusive SC crystallization and extremely low melt viscosity) and the lack of necessary functional features (e.g., electrical conductivity) in some cases. Herein, we devise a facile and robust strategy to overcome these obstacles by incorporating carbon black (CB) into equimolar poly(L-lactide)/poly(D-lactide) (PLLA/PDLA) blend. It is interesting to find that the CB particles can adsorb many PLLA/PDLA chain segments on their surface and such strongly adsorbed PLA segments could interact with PLA chains outside the surface to form physical junctions capable of stabilizing the PLLA/PDLA chain assemblies in the melt, finally inducing the exclusive SC formation during subsequent crystallization. Meanwhile, the CB particles can substantially enhance the melt viscosity of the blend (from 3.9 Pa s to 844.1 Pa s when measuring at 250 °C and 50 Hz). Because of the greatly improved melt-processability, the PLLA/PDLA/CB composites have been successfully processed into highly crystalline products with exclusive SC crystallites and excellent thermomechanical performance by injection molding. Additionally, the CB particles can endow the composite products with fascinating electrical conductivity (19.0 S/m) and electromagnetic interference shielding effectiveness (26.6 dB). This work could open up a promising avenue towards high-performance and multifunctional PLA engineering Bioplastic. Image 1 • CB particles are used to improve the melt-processability and electrical performance of SC-PLA. • The CB particles exhibit strong adsorbability for PLLA/PDLA chain segments. • The adsorbed PLA segments contribute to the greatly enhanced melt memory effect and melt viscosity. • The PLLA/PDLA/CB composites can be injection molded into products with exclusive SC crystallites. • The obtained products possess superb thermomechanical and electrical properties. [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]

The branching structure formed by α terminal of natural rubber (NR) was believed to be critical for its superior mechanical properties. However, it is challenging to unravel and mimic the relationship between the terminal structures and properties of NR due to the complexity of the system. Herein we synthesized a model compound containing phosphate groups at the end of the polyisoprene rubber to explore the role of α-terminal. After a series of tests, it is found that the phosphate groups formed branching points with or without iron ions. TEM test showed that sizes of aggregates formed by phosphate groups changed to be smaller after addition of FeCl 3. Water contact angle test verify the formation of branching structures. Rheology test showed that branching structures increased their storage modulus G' compared to linear polymer. The effects of phosphate groups aggregations on the chain dynamics were also investigated. Dielectric relaxation analysis indicated that the branching structure formed by phosphate groups confined the chain movement. All the above results help us to get a deeper understanding on the structural formation and function about α-terminal groups of NR. Image 1 • A model compound containing phosphate groups at the end of the polyisoprene chain was synthesized. • The branching structure formed by phosphate groups was confirmed. • The effects of branching structure on storage modulus and chain dynamics were investigated. [ABSTRACT FROM AUTHOR]

Abstract: Stereocomplex (SC) crystallization between poly( l‐lactide) (PLLA) and poly( d‐lactide) (PDLA) exhibits tremendous potential to improve the properties of polylactide (PLA), but the practical processing of SC‐type PLA (SC‐PLA) is significantly hindered by the insufficient melt stability and serious degradation after complete melting of SC crystallites over 240 °C. In a previous work, powder metallurgy inspired low‐temperature (180–210 °C) compression sintering is proposed to fabricate SC‐PLA products from its nascent powder. However, its industrial application is still challenging mainly due to the low production efficiency (half an hour is required) as well as the weak ability to fabricate products with complex shapes. In this work, an effort to rapidly fabricate complex‐shaped SC‐PLA products using low‐temperature injection molding technology is reported, where SC‐PLA nascent powder is partially melted. To ensure appropriate powder flowability, small amounts of glyceryl monostearate are incorporated as a lubricant. The results show that, both the self‐nucleation and flow‐induced nucleation effects facilitate the SC crystallization across the interfaces between adjacent unmelted powder particles, which considerably shortens the sintering cycle to about 2 min. In this way, complex‐shaped SC‐PLA products (such as gears) with superb performance are successfully fabricated by injection molding for the first time. [ABSTRACT FROM AUTHOR]

A novel class of wide-range linear viscoelastic hydrogels are fabricated by designing a homogeneous network with multiple coordination interactions of different bonding strength. The network enables affine deformation and progressive dissociation of coordination interaction from weak to strong ones, leading to the wide-range linear viscoelasticity and the strong yet compliant mechanical properties. These properties are highly advantageous for the practical applications of the hydrogels as quantifiable stress-strain sensors and soft robotics. • Hydrogels are designed by a homogenous network with multi coordination interactions. • Such designing principles enable affine extension and progressive dissociation. • Hydrogels manifest wide-range linear viscoelasticity with high mechanical properties. • Hydrogels can be used as quantifiable stress-strain sensors. Wide-range linear viscoelastic materials with high mechanical properties have not been reported yet, despite their bright prospect in diverse applications. Herein, we fabricate a class of physical hydrogels manifesting linear stress-strain relationship up to a strain of 1700%, high tensile stress up to 12.0 MPa and fracture toughness up to 82.1 MJ/m3, yet the materials are quite soft with Young's modulus from 0.2 to 1.1 MPa. Such physical hydrogels are formed by designing a homogeneous network with multiple coordination interactions of different bonding strength. Under small deformation, the homogeneous network enables affine deformation featured by entropic elasticity with negligible energy dissipation. Further increasing the deformation, the elongated network chains progressively break the weak to strong coordination interactions, which not only leads to a linear increase in stress, but also generates constant growth in energy dissipation. Moreover, the hydrogels show linear relative resistance change-strain-stress behavior, and thus can be used as quantifiable stress-strain sensors to simultaneously monitor deformation and force of soft robotics, wearable devices, flexible electronics, rehabilitation and sport equipments. [ABSTRACT FROM AUTHOR]