Energy absorbing polymer-based composites

The ability of polymer-based fibre reinforced composite materials to absorb energy when subjected to high stress depends on the micromechanics of deformation and fracture of the individual laminae and the interaction between laminae. The micromechanismsdepend on the properties of the matrix, fibres and fibre-matrix interface. The capacity of material to absorb energy is important in many applications and particular reference is made to the response of structures to impact.     

Thermoplastic Cellulose-Based Compound for Additive Manufacturing

The increasing environmental awareness is driving towards novel sustainable high-performance materials applicable for future manufacturing technologies like additive manufacturing (AM). Cellulose is abundantly available renewable and sustainable raw material. This work focused on studying the properties of thermoplastic cellulose-based composites and their properties using injection molding and 3D printing of granules. The aim was to maximize the cellulose content in composites. Different compounds were prepared using cellulose acetate propionate (CAP) and commercial cellulose acetate propionate with plasticizer (CP) as polymer matrices, microcellulose (mc) and novel cellulose-ester additives; cellulose octanoate (C8) and cellulose palmitate (C16). The performance of compounds was compared to a commercial poly(lactic acid)-based cellulose fiber containing composite. As a result, CP-based compounds had tensile and Charpy impact strength properties comparable to commercial reference, but lower modulus. CP-compounds showed glass transition temperature (Tg) over 58% and heat distortion temperature (HDT) 12% higher compared to reference. CAP with C16 had HDT 82.1 °C. All the compounds were 3D printable using granular printing, but CAP compounds had challenges with printed layer adhesion. This study shows the potential to tailor thermoplastic cellulose-based composite materials, although more research is needed before obtaining all-cellulose 3D printable composite material with high-performance.     

In-situ synthesis of 3D printable mono- and Bi-metallic (Cu/Ag) nanoparticles embedded polymeric structures with enhanced electromechanical properties

The interest of additive manufacturing with 3D printing increases day by day, which provides improved mechanical, electrical, magnetic and thermal properties of 3D parts. The production of 3D parts with the stereolithography (SLA) method, which allows it to be produced with high precision, resolution and complex geometries, distinguishes itself from other alternative additive manufacturing methods (FDM. SLS. LOM. LMD etc.). However, studies on the preparation of functional 3D polymer nanocomposites with the SLA method are quite limited. This study aims to produce silver (Ag) and/or copper (Cu) based 3D polymer nanocomposites for enhancing its mechanical strength, thermal stability and electrical conductivity. Mono and bimetallic (Cu/Ag) nanoparticles have been in-situ synthesized by selective irradiation of laser beam method using a commercial SLA device. In this method, metal (Cu/Ag) acrylate containing photocurable resin is not only cured but also leads to thermal decomposition of metal ions into nanoparticles to form functional 3D structures. The mechanical, electrical and thermal properties of polymer nanocomposites are characterized in detail. As a result of the analysis, the nanoparticles, with an average diameter of 25–55 nm, are well dispersed in the polymer matrix without agglomeration. The temperature at which 5% weight loss of Ag and Cu based polymer structures is measured as 179.3 °C while the glass transition temperature is found to be 223.81 °C. Most importantly, the resistance values are significantly decreased from 456.62 GΩ (Gigaohm) to 1.50 GΩ by increasing the amount of Ag addition at 3D polymeric structures. Therefore, this study allows the production of polymer nanocomposites not only in complex structures but also in desired properties especially for electrically conductive materials, capacitors and electronic applications.     

Bio‐inspired Design and Additive Manufacturing of Soft Materials,Machines, Robots,and Haptic Interfaces

Soft materials possess several distinctive characteristics, such as controllable deformation, infinite degrees of freedom, and self‐assembly, which make them promising candidates for building soft machines, robots, and haptic interfaces. In this Review, we give an overview of recent advances in these areas, with an emphasis on two specific topics: bio‐inspired design and additive manufacturing. Biology is an abundant source of inspiration for functional materials and systems that mimic the function or mechanism of biological tissues, agents, and behaviors. Additive manufacturing has enabled the fabrication of materials and structures prevalent in biology, thereby leading to more‐capable soft robots and machines. We believe that bio‐inspired design and additive manufacturing have been, and will continue to be, important tools for the design of soft robots.     

SEM-EDS and XPS Studies of the High Temperature Oxidation Behaviour of Inconel 718

 The oxidation in air under isothermal conditions of Inconel 718 has been investigated at 900 °C. We have studied the firsts stages of the high temperature oxidation mechanism. The oxidised samples were examined using a number of surface analytical techniques including XPS and SEM-EDS. The results have shown that minor alloying elements strongly influence the oxidation behaviour of the alloy: Previous studies had shown that the rate of the external oxide scale growth and the intergranular oxide penetration during oxidation of Inconel 718 at 900 °C in air are lower than those of Inconel X or Incoloy 800. We suggest that the formation of a quasi continuous scale of the intermetallic phase Ni₃Nb at the oxide-alloy interface could have an important contribution to the good oxidation resistance of Inconel 718.     

Polymer 4D printing: Advanced shape-change and beyond

4D printing is an exciting branch of additive manufacturing. It relies on established 3D printing techniques to fabricate objects in much the same way. However, structures which fall into the 4D printed category have the ability to change with time, hence the “extra dimension.” The common perception of 4D printed objects is that of macroscopic single-material structures limited to point-to-point shape change only, in response to either heat or water. However, in the area of polymer 4D printing, recent advancements challenge this understanding. A host of new polymeric materials have been designed which display a variety of wonderful effects brought about by unconventional stimuli, and advanced additive manufacturing techniques have been developed to accommodate them. As a result, the horizons of polymer 4D printing have been broadened beyond what was initially thought possible. In this review, we showcase the many studies which evolve the very definition of polymer 4D printing, and reveal emerging areas of research integral to its advancement.     

SiO2/聚合物核壳型杂化粒子及其空心结构的制备

SiO2/聚合物核壳型杂化粒子及其空心结构以其独特的形貌在药物控制释放、催化剂载体、生物医药等领域应用前景广阔,引起了人们的广泛关注。本文着重从乳液聚合法、仿生矿化法等制备方法角度阐述了SiO2/聚合物核壳型杂化粒子及其空心结构的研究进展。乳液聚合制备SiO2/聚合物核壳型杂化粒子简单易行,一般需要预先合成SiO2纳米粒子,其合成过程通常需要一些非理想的条件,如高温高压、极端pH、昂贵或有毒的有机试剂等,而且预先合成的SiO2粒子无法与聚合物实现100%匹配,即总有纯的聚合物粒子存在。相比之下,原位仿生矿化法制备SiO2杂化粒子不仅在环境条件下可进行,而且能够精确控制其纳米尺度的形态及分级有序结构。目前对材料科学家来讲,要使人工合成SiO2/聚合物杂化粒子实现像自然生物硅那样优异的性能,仍然是很大的挑战。     

Statistical analysis of mechanical properties of wood-PLA composites prepared via additive manufacturing

Additive manufacturing circumscribes numerous technologies that allow for the construction of three-dimensional parts by superimposing layers of material. These technologies have undergone greater development in recent years. In this work, using 3D additive printing technology, the samples are prepared using biodegradable wood-PLA composite by varying the layer height (0.08?mm, 0.16?mm, and 0.24?mm), infill (30%, 60%, and 90%) and three different patterns such as layer, triangle, and hexagon. Using universal testing machines tensile properties, energy absorption, and toughness of samples are evaluated as per ASTM standards. The results show that better values are achieved with increase in the infill percentage and layer pattern provides better strength and stiffness. A statistical linear regression model was successfully developed to predict the mechanical properties with an accuracy of 96% predicted in layer pattern when compared to other. Linear regression method helps to find the relationships between two sub-properties of mechanical property of different types of materials and helps to predict the properties of unknown materials.     

Comparison between the Test and Simulation Results for PLA Structures 3D Printed,Bending Stressed

The additive manufacturing process is one of the technical domains that has had a sustained development in recent decades. The designers’ attention to equipment and materials for 3D printing has been focused on this type of process. The paper presents a comparison between the results of the bending tests and those of the simulation of the same type of stress applied on 3D-printed PLA and PLA–glass structures. The comparison of the results shows that they are close, and the simulation process can be applied with confidence for the streamline of filament consumption, with direct consequences on the volume and weight of additive manufactured structures. The paper determines whether the theories and concepts valid in the strength of materials can be applied to the additive manufacturing pieces. Thus, the study shows that the geometry of the cross-section, by its shape (circular or elliptical) and type (solid or ring shaped), influences the strength properties of 3D-printed structures. The use of simulation will allow a significant shortening of the design time of the new structures. Moreover, the simulation process was applied with good results on 3D-printed structures in which two types of filaments were used for a single piece (structure).     

An investigation into compressive responses of shape memory polymeric cellular lattice structures fabricated by vat polymerization additive manufacturing

A combination of additive manufacturing techniques with shape memory materials, so that the shape, property, or functionality of a 3D printed structure can change as a function of time, has recently created new progress in 4D printing. Low-density lattice structures, due to their unique mechanical properties and engineering characteristics, have been candidates for lightweight structures and energy absorbing applications. In the present work, Rhombic and Body-Centered Cubic (BCC) cellular lattice structures, as well as cylindrical bulk samples, were designed and fabricated with Digital Light Process (DLP) by using shape memory resin. The energy absorption of SMP samples was studied in terms of the capabilities of absorption and recovery. In addition, deformation mechanisms of the structures, the influence of strain rate, cyclic behavior and the strain recovery of the structures after each cycle were investigated. All the studies were done in three different cold, warm and hot programming schemes to evaluate the effects of temperature on shape memory effect of the products. Although both structures showed nearly the same strain recovery rates at all conditions, Rhombic structure was found to possess better functional and structural behaviors than BCC lattice in terms of strength, stiffness, and absorption as well as recovery of the induced energy.     

pH responsive adhesion of phospholipid vesicle on poly(acrylic acid) cushion grafted to poly(ethylene terephthalate) surface

Polymer-supported lipid bilayer is a key enabling technology for the design and fabrication of novel biomimetic devices. To date, the physical driving force underlying the formation of polymer-supported lipid bilayer remains to be determined. In this study, the interaction between dipalmitoylphosphocholine (DPPC) vesicle and poly(ethylene terephthalate) [PET] surface with or without grafted poly(acrylic acid) [PAA] layer is examined with several biophysical techniques. First, vesicle deformation analysis shows that the geometry of adherent vesicle on either plain PET or PAA-grafted PET surface is best described by a truncated sphere model. At neutral pH, the degree of deformation and adhesion energy are unaltered by the grafted polymerization of acrylic acid on PET surface. Interestingly, the average magnitude of adhesion energy is increased by 185% and −43% on PAA-grated PET and plain PET surface, respectively, towards an increase of pH at room temperature. Our results demonstrate the possibility of tuning the adhesive interaction between vesicle and polymer cushion through the control of polyelectrolyte ionization on the solid support.     

Additive manufacturing of fire‐retardant ethylene‐vinyl acetate

Thermocompression (with also extrusion and injection molding) is a classical polymer shaping manufacturing, but it does not easily allow designing sophisticated shapes without using a complex mold, on the contrary to 3D printing (or polymer additive manufacturing), which is a very flexible technique. Among all 3D printing techniques, fused deposition modeling is of high potential for product manufacturing, with the capability to compete with conventional polymer processing techniques. This is a quite low cost 3D printing technique, but the range of filaments commercially available is limited. However, in some specific 3D printing processes, no filaments are necessary. Polymers pellets feed directly the printing nozzle allowing to investigate many polymeric matrices with no commercial limitation. This is of high interest for the design of flame‐retarded materials, but literature is scarce in that field. In this paper, a comparison between thermocompression and 3D printing processes was performed on both neat ethylene‐vinyl acetate (EVA) copolymer and EVA flame retarded with aluminum triHydroxyde (ATH) containing different loadings (30 or 65 wt%) and with expandable graphite (EG), ie, EVA/ATH (30 wt%), EVA/ATH (65 wt%), and EVA/EG (10 wt%), respectively. Morphological comparisons, using microscopic and electronic microprobe analyses, revealed that 3D printed plates have lower apparent density and higher porosity than thermocompressed plate. The fire‐retardant properties of thermocompressed and 3D printed plates were then evaluated using mass loss calorimeter test at 50 kW/m². Results highlight that 3D printing can be used to produce flame‐retardant systems. This work is a pioneer study exploring the feasibility of using polymer additive manufacturing technology for designing efficient flame‐retarded materials.     

Polymer Networks: From Plastics and Gels to Porous Frameworks

Polymer networks, which are materials composed of many smaller components—referred to as “junctions” and “strands”—connected together via covalent or non‐covalent/supramolecular interactions, are arguably the most versatile, widely studied, broadly used, and important materials known. From the first commercial polymers through the plastics revolution of the 20^th century to today, there are almost no aspects of modern life that are not impacted by polymer networks. Nevertheless, there are still many challenges that must be addressed to enable a complete understanding of these materials and facilitate their development for emerging applications ranging from sustainability and energy harvesting/storage to tissue engineering and additive manufacturing. Here, we provide a unifying overview of the fundamentals of polymer network synthesis, structure, and properties, tying together recent trends in the field that are not always associated with classical polymer networks, such as the advent of crystalline “framework” materials. We also highlight recent advances in using molecular design and control of topology to showcase how a deep understanding of structure–property relationships can lead to advanced networks with exceptional properties.     

Synthesis and Morphogenesis of Organic and Inorganic Polymers by Means of Biominerals and Biomimetic Materials

We have studied the simultaneous synthesis and morphogenesis of polymer materials with hierarchical structures from nanoscopic to macroscopic scales. The morphologies of the original materials can be replicated to the polymer materials. In general, it is not easy to achieve the simultaneous synthesis and morphogenesis of polymer material even using host materials. In the present work, four biominerals and three biomimetic mesocrystal structures are used as the host materials or templates and polypyrrole, poly(3‐hexylthiopehene), and silica were used as the precursors for the simultaneous syntheses and morphogenesis of polymer materials. The host materials with the hierarchical structure possess the nanospace for the incorporation of the monomers. After the incorporation of the monomers, the polymerization reaction proceeds in the nanospace with addition of the initiator agents. Then, the dissolution of the host materials leads to the formation and morphogenesis of the polymer materials. The scheme of the replication can be classified into the three types based on the structures of the host materials (types I–III). The type I template facilitates the hierarchical replication of the whole host material, type II mediates the hierarchical surface replication, and type III induces the formation of the two‐dimensional nanosheets. Based on these results, the approach for the coupled synthesis and morphogenesis can be applied to a variety of combinations of the templates and polymer materials.     

Design and synthesis of self-healing polymers

Self-healing polymers represent a class of materials with built-in capability of rehabilitating damages. The topic has attracted increasingly more attention in the past few years. The on-going research activities clearly indicate that self-healing polymeric materials turn out to be a typical multi-disciplinary area concerning polymer chemistry, organic synthesis, polymer physics, theoretical and experimental mechanics, processing, composites manufacturing, interfacial engineering, etc. The present article briefly reviews the achievements of the groups worldwide, and particularly the work carried out in our own laboratory towards strength recovery for structural applications. To ensure sufficient coverage, thermoplastics and thermosetting polymers, extrinsic and intrinsic self-healing, autonomic and non-autonomic healing approaches are included. Innovative routes that correlate materials chemistry to full capacity restoration are discussed for further development from bioinspired toward biomimetic repair.     

Three-Dimensional Bioprinting of Decellularized Extracellular Matrix-Based Bioinks for Tissue Engineering

Three-dimensional (3D) bioprinting is one of the most promising additive manufacturing technologies for fabricating various biomimetic architectures of tissues and organs. In this context, the bioink, a critical element for biofabrication, is a mixture of biomaterials and living cells used in 3D printing to create cell-laden structures. Recently, decellularized extracellular matrix (dECM)-based bioinks derived from natural tissues have garnered enormous attention from researchers due to their unique and complex biochemical properties. This review initially presents the details of the natural ECM and its role in cell growth and metabolism. Further, we briefly emphasize the commonly used decellularization treatment procedures and subsequent evaluations for the quality control of the dECM. In addition, we summarize some of the common bioink preparation strategies, the 3D bioprinting approaches, and the applicability of 3D-printed dECM bioinks to tissue engineering. Finally, we present some of the challenges in this field and the prospects for future development.     

Fabrication of Photoprocessable Materials via Photopolymerization Using an Acid-Induced Photocleavable Platinum-Acetylide Crosslinker

Photopolymerization and photoprocessing are core technologies for molding and tuning polymer materials. However, they are incompatible with single materials owing to their contradictory photoreactivity. Herein, an acid-induced photocleavable crosslinker, a platinum–acetylide complex covered by permethylated cyclodextrins, enables the fabrication of photoprocessable materials via photopolymerization with N-(2-hydroxyethyl)acrylamide. The polymer networks are molded by 365 nm irradiation as well as softened and degraded by a cooperative reaction with HCl as an acidic additive under 365 nm UV light, or 470 nm visible light in the presence of a photosensitizer. Moreover, the crosslinker is applied to a photoadhesive triggered by 365 nm irradiation. The adhesion is detachable on-demand through acid-induced photodegradation with the same wavelength and intensity of irradiation. Thus, acid-induced photocleavage allows the integration of light-induced molding and processing under various lights of various wavelengths, opening up new strategies for polymer technologies.     

Understanding the impact properties of polymeric sandwich structures used for motorcyclists' back protectors

Conventional back protectors are comprised of two main parts: elastomeric foams to absorb the impact energy; and thermoplastic polymers to distribute the impact force on a wider area before the absorption process. Thermal comfort is usually maintained by vent holes within the structure. In the present work, the impact behavior of a number of samples made of materials commonly used for manufacturing such protectors was studied. Nitrile butadiene rubber as the soft layer and polyethylene thermoplastic as the hard layer were considered. The variables for the analyses were the thickness of the layers, the sample temperature and the distribution of the vent holes in the sample. The key findings are: the force distribution capability of the hard part and the stability of the impact properties with respect to temperature variations are fairly dependent on the thickness of the soft part; and a reasonable distance between two consecutive vent holes is required for achieving optimal impact protection.     

Enhanced self-healing driving force in polymer materials by regulating molecular structure

For self-healing polymers, obtaining excellent healing ability and mechanical properties usually need complex chemical structure, external healing conditions, and high manufacturing difficulty. Therefore, self-healing efficiency and rate, mechanical strength, and simple structure design as well as no additional healing conditions of the material are contradictory properties and are difficult to optimize simultaneously. Herein, self-healable thermoplastic poly (urethane urea) elastomers driven by surface energy were fabricated by the introduction of asymmetric alicyclic structures and the healing properties in polymers were optimized by regulating surface energy. The results showed that with the increasing of isophorone diamine contents, the surface energy driving force increased from 36 kPa to 149 kPa, the healing time decreased from 30d to 5d, and healing efficiency, and tensile strength reached 100.9% and 4.04 MPa at room temperature. At the same time, polymers also obtained a high healing efficiency under high-temperature healing conditions. The healing mechanism is that asymmetric alicyclic structures with steric hindrance and ring flip promote the dissociation of hydrogen bonds, provide sufficient chain mobility, decrease the junction density, and improve the surface energy as well as the dissociation and reconstruction of hydrogen bonds. Energetic polymer composites using thermoplastic poly (urethane urea) elastomers as matrix obtained excellent healing properties. This study will offer a novel healing approach for developing advanced self-healing polymer materials.     

Biomimetic Fabrication of Polymer Film with High Adhesive Superhydrophobicity by Duplicating Locust Wing Surface

Locust is a common flying insect. Locust wings were used as biomimetic templates to fabricate multi-functional polymer(polydimethylsiloxane, PDMS) films by soft lithography. The microstructure and wettability of the natural and artificial locust wing surfaces were investigated by means of a scanning electron microscope(SEM) and a video-based contact angle meter. The natural locust wing surface exhibits complicated hierarchical structures and high adhesive superhydrophobicity(contact angle 152°). The prepared polymer film faithfully reproduces the surface microstructures of the bio-template, and displays a good hydrophobicity and high adhesion(contact angle 144°). The complex wettability of the natural and artificial locust wing surfaces ascribes to the cooperative effect of hydrophobic composition and multi-dimensional rough microstructures. This work not only promotes our understanding of the wetting mechanism on bio-surfaces, but offers an inexpensive and effective approach for biomimetic fabrication of multi-functional interfacial materials.