Polyurethane-polyisocyanurate rigid (PIR) foams are used as thermal insulation materials in a wide range of applications such as construction and pipe insulation. Some of the utilizations require the maximum operating temperature of these materials to reach extremely high temperatures. This work is devoted to the study of changes in the chemical composition and the main physical-mechanical and thermophysical characteristics of PIR foams subjected to prolonged extreme heating in the presence of the material direct contact with air and in its absence. Based on the results obtained, prolonged extreme heating of such materials leads to a significant change in their chemical composition, mainly due to the thermal decomposition of allophanate, urethane and urea linkages, as well as the gradual formation of uretidione, linear carbodiimide polymer and the oxidation of ethers to esters. The relative compressive strength of these materials changes only to a small extent, while the thermal conductivity of these materials increases significantly during heating.

The overarching goal in sports gears to achieve higher levels of impact protection without an increased weight penalty motivated the pursuit of density gradation in cellular solids. The research reported herein studied the impact performance of density-graded polyurea elastomeric foams, including different gradation and interfacing strategies. The latter leveraged the natural adhesion properties of polyurea foam slurry to sequentially assemble graded structures with seamless interfaces. Moreover, conventional discretely graded polyurea foam structures were manufactured using bulk polyurea adhesive by individually bonding pre-fabricated sheets. Six density-graded foam configurations were characterized, including bi- and tri-layered foams with naturally bonded or adhered interfaces. Additionally, standard mono-density polyurea and another benchmark foams were tested as controls. Extracted samples were submitted to impact loading using an instrumented drop weight tower. The impact efficacy of the foams was analyzed using three dynamic performance metrics (DPMs), including the specific energy absorptivity (SEA), absorption efficiency, and local buckling-induced undulation, based on the averaged stress-strain response. The mono-density polyurea foam reported the largest SEA, outperforming all density-graded foam configurations. The limited density gradation is attributed to the inferior performance of graded structures. A brief biomechanics case study is presented to assess the potential interrelationship between the investigated foam structures and the head injury criterion (HIC), showing the superior performance of adhered trilayer polyurea foams. Finally, the average stress-strain responses were fitted using an empirical model, elucidating the effect of strain rates and base materials on their overall impact behavior.

Using small amounts of multi-walled carbon nanotubes (MWCNTs) functionalized with carboxyl groups, methyldiethanolamine and triethanolamine (from 0.005 to 0.1%), a series of rigid composite polyurethane-polyisocyanurate (PIR) and polyurethane (PUR) foams was obtained. The influence of these additives on the morphology of the cellular structure of the synthesized foams, as well as the change in their physical-mechanical and thermophysical characteristics, was analyzed. The effect of additions of functionalized MWCNTs on the change in compressive strength, Young’s modulus, thermal conductivity index, and mass loss during combustion of the synthesized foams has been studied. Based on the results obtained, the introduction of small amounts (up to 0.05%) of functionalized nanotubes in the foam composition improves the characteristics described above. The greatest effect was achieved using 0.05% carboxylated MWCNTs functionalized with triethanolamine.

In this current study, rigid polyurethane foams (RPUFs) composites were prepared using different percentage (3, 6, 9 and 12%) of the hemp fibers via one-shut one-step polymerization method. The influences of the hemp fiber addition on the RPUFs were investigated meticulously by means of Fourier-transform infrared spectroscopy (FTIR), thermo gravimetric analysis (TGA), thermal conductivity measurement and scanning electron microscopy (SEM) techniques by evaluating the alternations in the chemical structures of the component, thermal stability, apparent density, insulation performance and cellular topology of the produced samples. The structural analysis revealed that there existed the strong secondary chemical bonds between the functional groups belonging to the components and, depending on that, the improvement in the thermal stability of the foam samples was recorded accompanied by the formation of the better interfacial adhesion. Furthermore, thermal conductivity values of the hemp fiber-loaded RPUFs were observed to increase regularly with the increasing of the content level of the hemp fibers. This was explained by enhancement in the bulk phase conduction level depending of the apparent density rising, reduction in CO 2 concentration inside cells as well as the formation of the distorted cellular structures. The obtained air permeability results displayed that the hemp fibers incorporated successfully with RPUF structure, which provides the occurrence of the novel micro barriers and pathways limiting the passage of the air throughout the matrix. The taken scanning electron microscopy images also indicated that the cellular morphology and dimensional stability of the produced foams affected negatively by the hemp fiber addition. At high contents, the wrinkled, non-uniform and irregular cellular structures were observed with ruptured and collapsed walls and struts.

Using methacrylic acid (MAA) and methyl methacrylate (MMA) as core monomers and polystyrene as the shell layer, polymer hollow microspheres (PHM) with good stability were prepared by using an alkali osmotic swelling method followed by spray drying. The average size of the PHM was approximately 875 nm. As a filling cross-linking agent, the PHM were added to a skin collagen material to disperse and fix, and a “polymer hollow microsphere composite collagen fiber” (PHCC) material was obtained. The results show that the PHM improve the mechanical strength, thermal stability and water resistance of the skin collagen material. The PHCC material has a low thermal conductivity (0.035 W/(K·m)) and excellent sound insulation performance and retains the soft and delicate touch of leather, which has application value in high-grade decorative materials and functional leather. This provides a new approach for developing flexible sound-absorbing thermal insulation materials.

In this work, polypropylene (PP) was foamed via rotational molding using a chemical blowing agent (CBA) based on azodicarbonamide over a range of concentration (0 to 0.5% wt.). The samples were then analyzed in terms of morphological, thermal and mechanical properties. The morphological analysis showed a continuous increase in the average cell size and cell density with increasing CBA content. Increasing the CBA content also led to lower foam density and thermal conductivity. Similarly, all the mechanical properties (tension, flexion and impact) were found to decrease with increasing CBA content. Finally, the efficiency of the rotomolding process was assessed by producing neat PP samples via compression molding. The results showed negligible differences between the rotomolded and compression molded properties at low deformation and rate of deformation indicating that optimal rotomolding conditions were selected.

The review summarises the trends in the development of research on the synthesis of polymethacrylimides (PMIs) and polyacrylimides by the method of intramolecular thermal imidisation of (meth)acrylic polymers. Along with the widely used industry variant of PMI foam of the ‘Rohacell’ series based on bulk copolymers of methacrylonitrile and methacrylic acid, intensive research on alternative variants began after 2005. This review describes the main and side reactions when using polymer precursors of different structures as well as the effect of precursor composition and structure on the properties of the resulting poly(meth)acrylimides. It has been shown that the achievements of the last 15 years provide a basis for reducing the cost of poly(meth)acrylimides which will significantly expand the areas and scale of their application.

Novel three-dimensional (3-D) hierarchical multiconfiguration graphene/polyaniline-based aerogels were synthesized via in situ polymerization and directed freeze-drying method. The composite aerogels enhanced excellent thermal and electrical performances, at the same time, their 3-D hierarchical multiconfiguration was robust and stable, which made them more beneficial to be applied to thermal or electrical fields. Graphene oxide/polyaniline (GO/AP) and reduced graphene oxide (RGO/AP) were prepared. The multiconfiguration structure can be apparently observed through scanning electron microscopy image of GO/AP aerogel: the aerogels were composed of skeleton structure with paralleled open holes; the skeleton structure was made up by hierarchical GO sheet with AP network; and the AP network consisted of AP skeleton and nanopores. GO/AP aerogels showed higher heat resistance than single AP aerogel. In addition, compared with GO/AP and AP aerogels, RGO/AP aerogel had the best electrical performances (vertical electrical conductivity: 1.23 S cm −1 and specific capacitance: 580 F g −1 ). What is more, attributed to the multiconfiguration structure, the composite aerogels exhibited excellent performances in holes extending direction.

Developing a multiple functional wound dressing suitable for different stages of wound healing is important for patients with special wound such as burn or decubital ulcers. In this study, poly (vinyl alcohol) (PVA), dextran, and chitosan are integrated to produce ideal wound dressing where glutaraldehyde (GA) is used as the cross-linker. The result demonstrated that 6% PVA hydrogel with 0.25% chitosan was found to provide antimicrobial ability. The PVA/chitosan hydrogel combined with 4% dextran utilizing GA cross-linking also presents the high cell proliferation ability, which suggests that the hydrogel is potential as a wound dressing. In the following physical analyses, the addition of chitosan and dextran appeared to promote the thermostability, mechanical properties, water retention, and moisturizing ability in the PVA hydrogel. In conclusion, the PVA/chitosan/dextran hydrogel has promising potential such as high water content, antimicrobial property, and well cell proliferation, which can be applied to wound healing application.

A continuous method without any solvent is proposed to produce porous hollow fibers for membrane (HFM) applications. In this case, linear low-density polyethylene was combined with azodicarbonamide to produce samples via extrusion. In particular, the processing (chemical blowing agent content and temperature profile) and post-processing (stretching velocity) conditions were optimized to obtain a cellular structure having a high cell density and uniform cell size distribution. From the samples obtained, a complete set of characterization was performed (morphological, mechanical, physical, and gas transport). The results show that HFM having a higher cell density can increase gas permeability, especially for hydrogen. Overall, it is shown that low-cost polyolefins having a suitable cellular structure can be used for gas separation membranes.