Eco-Friendly Flame-Retardant Phase-Change Composite Films Based on Polyphosphazene/Phosphorene Hybrid Foam and Paraffin Wax for Light/Heat-Dual-Actuated Shape Memory

Multiactuated shape memory materials are a class of promising intelligent materials that have received great interest in the fields of self-healing, anticounterfeiting, biomedical, soft robotic, and smart thermal management applications. To obtain a light/heat-dual-actuated shape memory material for thermal management applications in fire safety, we have designed a type of halogen-free flame-retardant phase-change composite film based on polyaryloxyphosphazene (PDAP)/phosphorene (PR) hybrid foam as a support material and paraffin wax (PW) as a phase-change material (PCM). PDAP was synthesized as a flexible foam matrix through the ring-opening polymerization of hexachlorocyclotriphosphazene, followed by a substitution reaction of aryloxy groups. The porosity of the PDAP foam is improved by introducing PR nanosheets, facilitating a high latent heat capacity of the PDAP-PR/PW composite films for thermal management applications. The PDAP-PR/PW composite films can implement rapid shape recovery within 65 s in the heating process, which is much shorter than that of the corresponding film without PR nanosheets (185 s). Furthermore, the PDAP-PR/PW composite films also exhibit light-actuated shape memory behavior thanks to their good solar-to-thermal energy absorption and conversion contributed by PR nanosheets as a highly effective photothermal material. More importantly, the presence of PR nanosheets imparts an excellent flame-retardant property to the PDAP-PR/PW composite films. The PDAP-PR/PW composite film can be self-extinguished within 2 s after the flame. Through an innovative integration of flexible polyphosphazene foam, PR nanosheets, and solid-liquid PCM to obtain a sensitive actuating response to light and heat, this study offers a new approach for developing multiactuated and eco-friendly flame-retardant shape memory materials to meet the requirement of applications with a requirement of fire safety in soft actuators, thermal therapy, control devices, and so on.

Morphological, Mechanical and Thermal Properties of Rubber Foams: A Review Based on Recent Investigations

During recent decades, rubber foams have found their way into several areas of the modern world because these materials have interesting properties such as high flexibility, elasticity, deformability (especially at low temperature), resistance to abrasion and energy absorption (damping properties). Therefore, they are widely used in automobiles, aeronautics, packaging, medicine, construction, etc. In general, the mechanical, physical and thermal properties are related to the foam's structural features, including porosity, cell size, cell shape and cell density. To control these morphological properties, several parameters related to the formulation and processing conditions are important, including foaming agents, matrix, nanofillers, temperature and pressure. In this review, the morphological, physical and mechanical properties of rubber foams are discussed and compared based on recent studies to present a basic overview of these materials depending on their final application. Openings for future developments are also presented.

Natural Rubber Blend Optimization via Data-Driven Modeling: The Implementation for Reverse Engineering

Natural rubber formulation methodologies implemented within industry primarily implicate a high dependence on the formulator’s experience as it involves an educated guess-and-check process. The formulator must leverage their experience to ensure that the number of iterations to the final blend composition is minimized. The study presented in this paper includes the implementation of blend formulation methodology that targets material properties relevant to the application in which the product will be used by incorporating predictive models, including linear regression, response surface method (RSM), artificial neural networks (ANNs), and Gaussian process regression (GPR). Training of such models requires data, which is equal to financial resources in industry. To ensure minimum experimental effort, the dataset is kept small, and the model complexity is kept simple, and as a proof of concept, the predictive models are used to reverse engineer a current material used in the footwear industry based on target viscoelastic properties (relaxation behavior, tanδ, and hardness), which all depend on the amount of crosslinker, plasticizer, and the quantity of voids used to create the lightweight high-performance material. RSM, ANN, and GPR result in prediction accuracy of 90%, 97%, and 100%, respectively. It is evident that the testing accuracy increases with algorithm complexity; therefore, these methodologies provide a wide range of tools capable of predicting compound formulation based on specified target properties, and with a wide range of complexity.

Effect of Vulcanization and CO2 Plasticization on Cell Morphology of Silicone Rubber in Temperature Rise Foaming Process

Both vulcanization reaction and CO₂ plasticization play key roles in the temperature rise foaming process of silicone rubber. The chosen methyl-vinyl silicone rubber system with a pre-vulcanization degree of 36% had proper crosslinked networks, which not only could ensure enough polymer matrix strength to avoid bubble rupture but also had enough dissolved CO₂ content in silicone rubber for induced bubble nucleation. The CO₂ diffusion and further vulcanization reaction occur simultaneously in the CO₂ plasticized polymer during bubble nucleation and growth. The dissolved CO₂ in the pre-vulcanized silicone rubber caused a temperature delay to start while accelerating further vulcanization reactions, but the lower viscoelasticity caused by either CO₂ plasticization or fewer crosslinking networks was still the dominating factor for larger cell formation. There was a sudden increase in elastic modulus and complex viscosity for pre-vulcanized silicone rubbers at higher temperature because of the occurrence of further vulcanization, but CO₂ plasticization reduced the scope of change of rheological properties, and the loss factor was close to 1 around 170 °C, which is corresponding to the optimum foaming temperature. The foamed silicone rubber had a higher cell density and smaller cell size at a higher temperature rising rate, which is due to higher CO₂ supersaturation and faster vulcanization reaction. These results provide some insight into the coupling mode and effect of CO₂ plasticization and vulcanization for regulating cell structure in foaming silicone rubber process.

Chemistry, Processing, Properties, and Applications of Rubber Foams

With the ever-increasing development in science and technology, as well as social awareness, more requirements are imposed on the production and property of all materials, especially polymeric foams. In particular, rubber foams, compared to thermoplastic foams in general, have higher flexibility, resistance to abrasion, energy absorption capabilities, strength-to-weight ratio and tensile strength leading to their widespread use in several applications such as thermal insulation, energy absorption, pressure sensors, absorbents, etc. To control the rubber foams microstructure leading to excellent physical and mechanical properties, two types of parameters play important roles. The first category is related to formulation including the rubber (type and grade), as well as the type and content of accelerators, fillers, and foaming agents. The second category is associated to processing parameters such as the processing method (injection, extrusion, compression, etc.), as well as different conditions related to foaming (temperature, pressure and number of stage) and curing (temperature, time and precuring time). This review presents the different parameters involved and discusses their effect on the morphological, physical, and mechanical properties of rubber foams. Although several studies have been published on rubber foams, very few papers reviewed the subject and compared the results available. In this review, the most recent works on rubber foams have been collected to provide a general overview on different types of rubber foams from their preparation to their final application. Detailed information on formulation, curing and foaming chemistry, production methods, morphology, properties, and applications is presented and discussed.

New trends in cellular silicone: Innovations and applications

The purpose of this article is to provide an overview of manufacturing processes used in the development of cellular silicone for a wide variety of applications. The combination of intrinsic properties of silicone and foam is considered as an attractive solution in many applications. With regard to the long-standing interest of the industry in silicone chemistry, foaming is very common from hydrosilylation/condensation reactions. This well-known technology leads to homogeneous, elastic, low density and biocompatible foams. However, the size of the cells remains large, the reactions are sensitive to humidity and the dangerousness of the hydrogen could be an industrial concern. Many researches are moving towards alternatives to the manufacture of silicone cellular materials such as gas foaming, phase separation, emulsion and sacrificial models, and syntactic charges. In addition, the theories of sorption, diffusion, nucleation and cell growth are detailed to explain the formation of gaseous foam. CO2 is commonly used to physically foam silicone because of its good solubility. However, the diffusive behavior of CO2 is high in silicone as explained by the free volume theory. Silicone–CO2 foaming is essentially triggered by rapid depressurization leading to a cell density around 1 × 109 cells/cm3 in the best case. In addition, templated foams are divided into emulsion polymerization (polyHIPE), sacrificial foams and syntactic foams. These methods are simple because they do not need specific foaming equipments. Pore sizes are also tunable as function of template sizes.

A new promising nucleating agent for polymer foaming: effects of hollow molecular-sieve particles on polypropylene supercritical CO2 microcellular foaming

Because polypropylene (PP) foam normally exhibits nonuniform cell size and cracked cellular structure, a narrow cell-size distribution and a well-defined morphology are always the focus of PP foaming technology. In this work, hollow molecular-sieve (MS) particles were applied as a potential nucleating agent in supercritical carbon dioxide (scCO2) foaming of PP. It was observed that the addition of MS particles largely narrowed the cell-size distribution. The resultant PP/MS foams exhibited significant concurrent enhancement in their cell density and mechanical properties: the cell density increased remarkably, by approximately 10 times, and the tensile strength increased from 6.1 MPa to 12.6 MPa. The hollow-structure MS particles resulted in a higher heterogeneous nucleation efficiency in the PP foaming process. We believe that the trapping of CO2 in the hollow holes of MS particles largely increased the solubility CO2 in PP and a number of gas cavities were formed. The existence of gas cavities reduced the energy barrier of heterogeneous nucleation, favoring the formation of a well-defined cellular structure. Additionally, the regular-hexagon shape of the cells might endow the PP foam with better mechanical properties compared with a circular cell shape.

Introduction of a long-chain branching structure by ultraviolet-induced reactive extrusion to improve cell morphology and processing properties of polylactide foam

Long-chain branching structure introduced by UV-induced reactive extrusion could widen its foaming processing window.