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There are principally two mechanisms to improve the impact resistance of polymer-based composites, intrinsic toughening and extrinsic toughening. But the interplay between them is far from being well understood. Here, glass fiber was incorporated into polypropylene to promote extrinsic toughening mechanism, while addition of elastomer and annealing were adopted for intrinsic toughening. In this way, the interaction among glass fiber, elastomer and annealing could be discussed based on various characterizations, and their combined effect on mechanical properties of the composites could be determined. The results show that the intrinsic toughening mechanism of elastomer will be suppressed by glass fiber irrespective of the support of annealing, though annealing could work synergistically with glass fiber to toughen polypropylene. The possible structure-property relations are discussed. This work will provide deeper insight into the toughening behavior of polymer composites and practical guidance for the design of composites with excellent stiffness-toughness balance. [ABSTRACT FROM AUTHOR]

Abstract: β-Modification and annealing were adopted to improve the impact strength of long glass fiber reinforced (LFPP) composites. It was found that either β-modification or annealing is an efficient way to toughen LFPP composites, and largely enhanced impact toughness can be achieved via simultaneously using β-modification and annealing, particularly for the toughness at low temperatures (−40°C to −20°C). Meanwhile, the tensile strength and Young’s modulus of the composites could be maintained. Various characterizations were used to understand the microstructure changes and toughening mechanism after β-modification and annealing. The results show that the higher extent of the matrix plastic deformation could be the main reason for the enhanced toughness as induced by β-modification and annealing. The possible structural origins for the higher extent of matrix plastic deformation are also discussed. [Copyright &y& Elsevier]

Cellular silicone foams are renowned for their exceptional flexibility, ultra-elasticity, and durability, which have gained significant attention in diverse applications. However, manufacturing porous silicone foams featuring substantial bending curvatures and customized mechanical properties remains a challenge. Herein, this work presents a new strategy for manufacturing curved porous silicone foams with both 4D printed bending curvature and tailored meta-mechanical properties. The foam is achieved by direct ink writing of composite silicone inks embedded with thermal expandable microspheres as foaming agents. The work studied in detail the thermal expansion of microspheres, foaming of composite silicone inks, as well as properties of the expanded foam. Utilizing the strain mismatch under thermal stimuli, the printed bilayer structures achieved shape-shifting. Additionally, silicones composed of stacked bilayer filaments exhibited negative stiffness properties under compression, leading to enhanced energy absorption capacity, which can be fine-tuned through different printing structural designs, demonstrating its potential in fields such as energy dissipation and shock absorption while protecting objects with curved shapes. This work presents a novel 4D printing strategy for manufacturing thin-shelled cellular silicone foams with both substantial bending curvature and tailored meta-mechanical properties. The foam is achieved by direct ink writing of composite silicone inks embedded with thermal expandable microspheres as foaming agents. This study investigated the thermal expansion of microspheres and composite silicone inks, as well as changes in the size, density, and modulus of the expanded silicone foam. By printing structures of stacked bilayer filaments with varying thermal expansion ratios, 4D printing of various geometrical structures due to strain mismatch, as well as negative stiffness effect due to snap- through buckling of stacked filaments under compression, were achieved. The combination of those characteristics demonstrated enhanced energy absorption capacity and potentials of the 4D printed cellular silicones in protecting objects with curved shapes from impact. [Display omitted] [ABSTRACT FROM AUTHOR]

Abstract: In this study, cellulose nanocrystals (CNCs) were incorporated into poly(propylene carbonate) (PPC), which is a biodegradable alternative copolymer of propylene oxide and carbon dioxide, CNCs were prepared by sulfuric treatment of cellulose filter. An effective approach to prepare PPC environment-friendly composites is shown. The obtained PPC/CNCs nanocomposites display orders of magnitude increase in mechanical properties by adding a small amount of CNCs, in particular, with only 0.1wt% of CNCs incorporated, a 10-fold increase in tensile strength and 7-fold increase in Young’s modulus were achieved. The thermal stability of the nanocomposites is significantly improved as measured by dynamic mechanical analysis and differential scanning calorimetry. This is due to a combination of CNCs reinforcement in the soft matrix and increased effective molecular weight of the nanocomposties. The present nanocomposites outperform PPC composites reinforced with other nano-sized stiff and anisotropic fillers. [Copyright &y& Elsevier]