Irena Pulko

The morphology of polyHIPE materials directly governs their permeability, surface area, and mechanical properties, therefore developing novel strategies to enhance emulsion uniformity and influencing the droplet size is crucial for advancing their practical applications. Methyl methacrylate (MMA) and ethylene glycol dimethacrylate (EGDMA) containing high internal phase emulsions (HIPEs) with internal phase volume fractions between 75% and 85% were prepared using a surfactant and homogenized with an overhead stirrer. Following emulsification, the HIPEs were either directly photopolymerised or first subjected to ultrasonic treatment and then photopolymerised. All resulting materials exhibited characteristic polyHIPE morphologies, comprising highly porous, interconnected structures. The primary pore diameters typically ranged from 3 to 23 μm. In all cases, ultrasound treatment resulted in a substantial reduction in average pore size, with decreases ranging from 10% to 50%, depending on the formulation. Morphological changes are attributed to acoustic cavitation and enhanced droplet disruption during sonication, confirming the influence of ultrasound on emulsion structure and the resulting pore architecture. Furthermore, compression testing showed that the improved pore uniformity introduced by sonication influences mechanical properties, resulting in higher compressive strength and increased elasticity compared to non-sonicated samples of the same composition.

The hybridisation of injection moulding (IM) and additive manufacturing (AM) offers the opportunity to combine the high productivity of IM and the high flexibility of AM into a single process. IM parts can be overprinted through fused filament fabrication (FFF) to allow for the customisation of parts or to add new functionalities. However, the right material pair must be chosen, and processing parameters must be optimised to achieve suitable adhesion between the components. The present study dealt with the investigation of the influence of the interfacial area, substrate surface roughness and overprinting processing parameters on the adhesion between the polyamide 6 (PA6) substrate and thermoplastic polyurethane (TPU) rib overprinted via FFF. PA6 substrates were produced through the IM of plates into a mould with different textures to obtain substrates with three different surface roughnesses. The ribs with varied interfacial areas were overprinted onto produced substrates using a desktop FFF 3D printer. To study the effect of overprinting processing parameters, the ribs were overprinted under varying printing and substrate temperatures and printing speeds according to the Box–Behnken design of experiments (DoE). The chemical composition and thermal properties of used materials were determined via attenuated total reflectance–Fourier transform infrared spectroscopy (ATR-FTIR), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA). The surface properties of prepared substrates were studied via digital optical microscopy (OM), through surface roughness measurements using a confocal microscope, through contact angle (CA) measurements and through the determination of free surface energy (SFE). The adhesion between the components was determined by evaluating the tear-off strength using a universal testing machine (UTM). With an increasing interfacial area, the tear-off strength decreased, while substrate surface roughness had no statistically significant effect. Overprinting parameters influenced the tear-off strength in the order of printing speed > printing temperature > substrate temperature. High values of tear-off strength were found for the lowest printing speed, while there were no important differences found between the middle and upper values. With increasing printing and substrate temperatures, the tear-off strength increased linearly. The highest value of tear-off strength (0.84 MPa) was observed at a printing temperature, substrate temperature and printing speed of 250 °C, 80 °C and 2 mm/s, respectively.

The processing of polymers and polymeric materials always leaves some residual stresses in the final product, which can have a positive but usually a negative effect on the properties of the final product. Polycarbonate was injection molded into the mold, which was heated to 50, 60, or 70°C to produce test specimens with different amounts of residual stresses. They were then annealed at various temperatures below T_g to partially remove the stresses or heated to 145°C (above T_g) to completely remove them. Comparison between annealed and as‐molded samples showed a strong influence of residual stresses on mechanical properties. Dynamic mechanical analysis (DMA) analysis showed that the loss modulus can be divided into the intrinsic loss modulus, which is a material property, and the residual stress, which can be relaxed at a given temperature. The stress relaxation curve, obtained by subtracting the loss modulus of the annealed sample from the loss modulus of the as‐molded sample gives us the ability to estimate the residual stresses that have been or can still be relaxed by heating to a given temperature.

The effects of three commercial aryl phosphate flame retardants (FRs; bisphenol A bis(diphenyl diphosphate) [BDP], triphenyl phosphate (TPP), and a proprietary oligomeric phosphate ester (OPE)) and a compatibilizer (methacrylate‐butadiene‐styrene copolymer [MBS]) on the thermal and mechanical properties of FR‐recycled PC/acrylonitrile‐butadiene‐styrene copolymer (r‐PC/r‐ABS) blends are investigated. The addition of FRs to r‐PC/r‐ABS blends increases the storage, tensile, and flexural moduli, indicating a reinforcing effect. However, at elevated temperatures, FRs reduce the glass transition temperature and act as plasticizers. The thermal stability of r‐PC/r‐ABS/FR blends at 10% mass loss increases in the following order: r‐PC/r‐ABS/TPP < r‐PC/r‐ABS/BDP < r‐PC/r‐ABS/OPE < r‐PC/r‐ABS/OPE/MBS. Kinetics of thermal decomposition of the FR r‐PC/r‐ABS blends is studied calculating the thermal decomposition activation energies by the Flynn–Wall–Ozawa method. Scanning electron microscopy shows that r‐PC/r‐ABS/OPE blend is only partly miscible, while homogeneous structure is formed in the r‐PC/r‐ABS/OPE/MBS blend, which is supported by its good mechanical and thermal properties. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020, 137, 48377.

Recently, a series of new monomers and polymerization mechanisms has been applied to the templating of high internal phase emulsions (HIPEs) providing a route to hierarchically porous materials with a range of functionalities and applications. The high degree of control over the pore size is another attractive feature of these materials. Usually, the continuous phase contains monomers, the droplet phase is used to template the large, primary pores, which are interconnected by secondary pores. The addition of nonpolymerizable components to the continuous phase can result in phase separation during polymerization and tertiary pores. Applications include polymer supports for catalysis and synthesis, separation and filtration, cell culture media, enzyme supports, and structural and isolation applications.