Graphene platelets versus phosphorus compounds for elastomeric composites: flame retardancy, mechanical performance and mechanisms.

Polymers are widely used but their flammability remains a serious issue causing fatalities and property damage. Herein we present an investigation into the effectiveness of graphene platelets (GnPs) to simultaneously improve the flame retardancy and mechanical properties of ethylene propylene diene monomer rubber (EPDM). EPDM was melt compounded respectively with GnPs and a commercial flame retardant (ammonium polyphosphate, APP) to produce two groups of composites. Although both fillers were well dispersed in EPDM, GnPs significantly improved the mechanical properties of EPDM whilst APP compromised some of the mechanical properties particularly at high fractions. This difference was attributed to the filler particle size and interfacial bonding. Through cone calorimetry testing, 21 wt% char yield was recorded for the EPDM/GnP composite at 12.0 vol%, in comparison with 8 wt% for the EPDM/APP composite. APP was able to lower the peak heat release rate (PHRR) and specific mass loss rate (MLR), but unfortunately it decreased the ignition time and fire performance index (FPI). By contrast, GnPs has been found to increase ignition time by 29% and FPI by 62%, while still achieved the same level of reductions in PHRR and specific MLR, demonstrating clear advantages over APP. During combustion the highly thermally stable GnPs bonded with the viscous, degraded EPDM macromolecules, forming a thick solid char layer which prevented the transport of heat and smoke, contributing to its superior flame retarding performance over APP.

Influence of growth rates, microstructural properties and biochemical composition on the thermal stability of mycelia fungi.

Mycelium fungal species exhibit fire retardant characteristics. The influence of the growth media on the fungal growth rates, biochemical composition, and microstructural characteristics and their relationship to thermal properties is poorly understood. In this paper, we demonstrate that molasses can support the growth of non-pathogenic Basidiomycota phylum fungal species producing bio-derived materials with potential fire retardation characteristics. Scanning electron microscopy and Fourier transform infrared (FTIR) spectrometry were used to interrogate the microstructural and biochemical properties of the molasses-grown mycelia species. Thermal decomposition of molasses-fed mycelia was evaluated via thermogravimetric analysis interfaced with FTIR for real-time evolved gas analysis. The morphological and microstructural characteristics of the residual char post-thermal exposure were also evaluated. The material characterization enabled the establishment of a relationship between the microstructural, biochemical properties, and thermal properties of molasses-fed mycelia. This paper presents a comprehensive exploration of the mechanisms governing the thermal degradation of three mycelial species grown in molasses. These research findings advance the knowledge of critical parameters controlling fungal growth rates and yields as well as how the microstructural and biochemical properties influence the thermal response of mycelia.

Towards antiviral polymer composites to combat COVID-19 transmission.

Polymer matrix composite materials have the capacity to aid the indirect transmission of viral diseases. Published research shows that respiratory viruses, including severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2 or COVID-19), can attach to polymer substrata as a result of being contacted by airborne droplets resulting from infected people sneezing or coughing in close proximity. Polymer matrix composites are used to produce a wide range of products that are "high-touch" surfaces, such as sporting goods, laptop computers and household fittings, and these surfaces can be readily contaminated by pathogens. This article reviews published research on the retention of SARS-CoV-2 and other virus types on plastics. The factors controlling the viral retention time on plastic surfaces are examined and the implications for viral retention on polymer composite materials are discussed. Potential strategies that can be used to impart antiviral properties to polymer composite surfaces are evaluated. These strategies include modification of the surface composition with biocidal agents (e.g., antiviral polymers and nanoparticles) and surface nanotexturing. The potential application of these surface modification strategies in the creation of antiviral polymer composite surfaces is discussed, which opens up an exciting new field of research for composite materials.

Novel Electrically Conductive Porous PDMS/Carbon Nanofiber Composites for Deformable Strain Sensors and Conductors.

Highly flexible and deformable electrically conductive materials are vital for the emerging field of wearable electronics. To address the challenge of flexible materials with a relatively high electrical conductivity and a high elastic limit, we report a new and facile method to prepare porous polydimethylsiloxane/carbon nanofiber composites (denoted by p-PDMS/CNF). This method involves using sugar particles coated with carbon nanofibers (CNFs) as the templates. The resulting three-dimensional porous nanocomposites, with the CNFs embedded in the PDMS pore walls, exhibit a greatly increased failure strain (up to ∼94%) compared to that of the solid, neat PDMS (∼48%). The piezoresistive response observed under cyclic tension indicates that the unique microstructure provides the new nanocomposites with excellent durability. The electrical conductivity and the gauge factor of this new nanocomposite can be tuned by changing the content of the CNFs. The electrical conductivity increases, while the gauge factor decreases, upon increasing the content of CNFs. The gauge factor of the newly developed sensors can be adjusted from approximately 1.0 to 6.5, and the nanocomposites show stable piezoresistive performance with fast response time and good linearity in ln(R/R0) versus ln(L/L0) up to ∼70% strain. The tunable sensitivity and conductivity endow these highly stretchable nanocomposites with considerable potential for use as flexible strain sensors for monitoring the movement of human joints (where a relatively high gauge factor is needed) and also as flexible conductors for wearable electronics (where a relatively low gauge factor is required).

Strain Sensors with Adjustable Sensitivity by Tailoring the Microstructure of Graphene Aerogel/PDMS Nanocomposites.

Strain sensors with high elastic limit and high sensitivity are required to meet the rising demand for wearable electronics. Here, we present the fabrication of highly sensitive strain sensors based on nanocomposites consisting of graphene aerogel (GA) and polydimethylsiloxane (PDMS), with the primary focus being to tune the sensitivity of the sensors by tailoring the cellular microstructure through controlling the manufacturing processes. The resultant nanocomposite sensors exhibit a high sensitivity with a gauge factor of up to approximately 61.3. Of significant importance is that the sensitivity of the strain sensors can be readily altered by changing the concentration of the precursor (i.e., an aqueous dispersion of graphene oxide) and the freezing temperature used to process the GA. The results reveal that these two parameters control the cell size and cell-wall thickness of the resultant GA, which may be correlated to the observed variations in the sensitivities of the strain sensors. The higher is the concentration of graphene oxide, then the lower is the sensitivity of the resultant nanocomposite strain sensor. Upon increasing the freezing temperature from -196 to -20 °C, the sensitivity increases and reaches a maximum value of 61.3 at -50 °C and then decreases with a further increase in freezing temperature to -20 °C. Furthermore, the strain sensors offer excellent durability and stability, with their piezoresistivities remaining virtually unchanged even after 10 000 cycles of high-strain loading-unloading. These novel findings pave the way to custom design strain sensors with a desirable piezoresistive behavior.