Low Density Resin Impregnated Ceramic Article Having an Average Density of 0.15 to 0.40 G/CC

A low-density resin impregnated ceramic article advantageously employed as a structural ceramic ablator comprising a fired preform of ceramic fibers. The fibers of the ceramic preform are coated with an organic resin film. The organic resin can be a thermoplastic resin or a cured thermosetting resin. In one embodiment, the resin is uniformly distributed within the ceramic article. In a second embodiment, the resin is distributed so as to provide a density gradient along at least one direction of the ceramic article. The resin impregnated ceramic article is prepared by providing a fired preform of ceramic fibers; immersing the preform of ceramic fibers in a solution of a solvent and an organic resin infiltrant; and removing the solvent to form a resin film on the ceramic fibers

Nitrogen-Rich Perylene Nanosheet Enhanced Bismaleimide Resin

The low toughness of bismaleimide resin (BMI) hinders its application in the aerospace field. In order to improve the strength and toughness of BMI resin simultaneously, this study proposes to introduce perylene-dicyandiamide (P-DCD) nanosheets with an ultra-s rigid conjugated planar structure into the polymer matrix of bismaleimide resin through hydrogen bonding and cross-linking to construct modified composites. The research results showed that the modified cured composites exhibited excellent mechanical properties, with a significant increase in impact strength of 135.8%, flexural strength and flexural modulus of 87.1% and 44.6%, respectively. The thermal properties of the resin were maintained before and after modification, with the glass transition temperature (Tg) of 284.0 ˚C and decomposition temperature > 520 ˚C. Meanwhile, the strengthening and toughening mechanism of the bismaleimide-based system modified by additive P-DCD were also explored. The results showed that the functional group of dicyandiamide in nanosheets and the hydrogen bonding effect in P-DCD synergically increased the cross-linking network and compatibility between P-DCD and the matrix resin

Synthesis and properties of a novel highly thermal stable N-propargyl monomer containing benzoxazole ring

© 2017, © The Author(s) 2017. A novel highly thermal stable propargyl functional compound containing benzoxazole ring, N, N, N′, N′-tetra propargyl-5-amino-2-(p-aminophenyl) benzoxazole (TPAPB), was proposed and synthesized using a phase-transfer catalytic method. The cure behavior of TPAPB was investigated by non-isothermal differential scanning calorimetry analysis. The solubility and rheological properties of TPAPB, as well as its broad temperature window from 130°C to 200°C with low viscosity, offered excellent processability for TPAPB to be used as a potential monomer of thermosetting polymer resin. It was found that the glass transition temperature of cured TPAPB was 359°C, and the temperature of 5% weight loss was 418°C in argon with the char residue up to 70% at 700°C. The polymerized resin exhibited high heat resistance and thermal stability, together with its processability, making it good candidate as highly heat-resistant polymer matrix for advanced composite applications

Surface characterization of LDEF carbon fiber/polymer matrix composites

XPS (x-ray photoelectron spectroscopy) and SEM (scanning electron microscopy) analysis of both carbon fiber/epoxy matrix and carbon fiber/polysulfone matrix composites revealed significant changes in the surface composition as a result of exposure to low-earth orbit. The carbon 1s curve fit XPS analysis in conjunction with the SEM photomicrographs revealed significant erosion of the polymer matrix resins by atomic oxygen to expose the carbon fibers of the composite samples. This erosion effect on the composites was seen after 10 months in orbit and was even more obvious after 69 months

Process–Structure–Properties in Polymer Additive Manufacturing

Additive manufacturing (AM) methods have grown and evolved rapidly in recent years. AM for polymers is an exciting field and has great potential in transformative and translational research in many fields, such as biomedical, aerospace, and even electronics. Current methods for polymer AM include material extrusion, material jetting, vat polymerisation, and powder bed fusion. With the promise of more applications, detailed understanding of AM—from the processability of the feedstock to the relationship between the process–structure–properties of AM parts—has become more critical. More research work is needed in material development to widen the choice of materials for polymer additive manufacturing. Modelling and simulations of the process will allow the prediction of microstructures and mechanical properties of the fabricated parts while complementing the understanding of the physical phenomena that occurs during the AM processes. In this book, state-of-the-art reviews and current research are collated, which focus on the process–structure–properties relationships in polymer additive manufacturing

The synthesis and characterization of conjugated polyradicals: an approach to organic magnets

The thesis describes investigations into the preparation and magnetic properties of new conjugated polymers, with pendant free radical sites, produced from substituted acetylenes. The first two chapters involve reviews of the literature concerning organic ferromagnetism and the preparation and structure of the materials produced by polymerizing phenylacetylene. The syntheses of esters of propiolic acid and propargyl alcohol, and their polymerization using metathesis catalysts are described in chapter three. The preparation of new substituted triphenyhnethanes and triphenylmethanols, and the syntheses of new ethynyl-substituted arylacetylenes, are described in chapters four and five, together with their full characterization. The polymerizations of phenylacetylene and the new substituted arylacetylenes using well-defined tungsten, molybdenum and rhodium catalysts are reported in chapter six, together with electron spin resonance and magnetic susceptibility studies. All the polymers produced in this study were found to be paramagnetic, and the main target polymer, poly((4-ethynylphenyl)diphenylmethyl) was found to display a reversible increase in spin concentration with increasing temperature. The conclusions drawn from these studies were that conjugated polyradicals were prepared, but that subsequent spin-pairing took place

LDEF Materials Workshop 1991, part 1

The workshop comprised a series of technical sessions on materials themes, followed by theme panel meetings. Themes included materials, environmental parameters, and data bases; contamination; thermal control and protective coatings and surface treatments; polymers and films; polymer matrix composites; metals, ceramics, and optical materials; lubricants adhesives, seals, fasteners, solar cells, and batteries. This report contains most of the papers presented at the technical sessions. It also contains theme panel reports and visual aids. This document continues the LDEF Space Environmental Effects on Materials Special Investigation Group (MSIG) pursuit of its charter to investigate the effects of LEO exposure on materials which where not originally planned to be test specimens and to integrate this information with data generated by principal investigators into an LDEF materials data base

Catalysis: from science to industry : proceedings of VII International scientific school-conference for young scientists, October 11-15, 2022

The collection is devoted to important and perspective directions of modern catalysis: fundamentals of catalyst preparation and catalytic processes, promising catalytic processes and industrial implementation of catalytic processes

Molecular Dynamics simulation of polyhedral oligomeric silsesquioxanes (POSS) and their polymeric nanocomposites

Within this thesis, I use atomistic Molecular Dynamics simulation to elucidate the thermomechanical properties of polyhedral oligomeric silsesquioxanes (POSS). These molecules have unique and interesting properties due to their nanoscale size and organic-inorganic nature. POSS species comprise a rigid silica core which is functionalised with organic moieties at the vertices. These nanoparticles exhibit a wide range of behaviours and properties due to the scope of viable functionalising groups. I largely focus here on the cubic T8 conformation, which typically ranges from 1-10 nm in diameter. For pure POSS systems, I use systematic simulation studies to characterise the sensitivity of the glass transition temperature (Tg), an important macroscopic property, to molecular structure. For POSS species functionalised with eight exible groups, I identify a key molecular feature, namely, the breathing mode, as the degree of freedom that controls the macroscopic Tg. Due to their high degree of inter-molecular entanglement, these systems exhibit very little molecular mobility. Thus, it is the molecular-level movements within the functionalising groups that underpin the systemic change from a glassy state to rubbery state. The in uence of structural morphology in tetra functionalised T8 systems are also studied. Here, I observe the adoption of richer packing arrangements and shifts in the Tg values due to alternative arrangements of the functionalising groups about the central core. I also examine the spontaneous formation of crystalline structures from amorphous starting configurations by systems of rigid POSS molecules. Due to the versatility in their structure, POSS are frequently included as a component in nanocomposite materials. Within this work, I have study POSS-polymer hybrids as both blended and grafted nanocomposites. I use hydroxyl-terminated polybutadiene (HTPB) for the polymer matrix and explain the observed changes in Tg as a product of the molecular behaviour and interactions. When grafted, POSS have a local anchoring effect on the dihedral rotational freedom available to the C-C single bonds of the HTPB backbone. Thus, I observe a significant increase in the Tg for these systems. When blended, rigid POSS hybrids exhibit significant phase separation, whereas flexible POSS species are much more dispersed within a HTPB matrix. Both systems impart less specific impact on the dihedral rotation of the HTPB matrix than is observed in the grafted systems. However, increases in Tg are consistently observed with increasing POSS concentration. Through the simulation of POSS blended with a chemically similar but sterically different matrix, I further characterise the mixing behaviours of POSS species as a function of their functionalising group. These studies provide insight into the structure-property relationship for a variety of POSS species as pure entities and nanocomposite hybrids, thus providing understanding for future programmes of synthesis or nanocomposite design, as well as necessary target properties for candidate coarse-grained models of POSS systems

IMIDE-FUNCTIONALIZED CONJUGATED POLYMERS: SYNTHESIS, STRUCTURE-PROPERTY AND DEVICE STUDIES

Organic semiconductors are widely studied as potential active components for consumer electronics due largely to their easily tuned properties and the promise of lower-cost solution-based processing technology. Imide-functionalized organic small molecule compounds have been one of the more important and studied organic semiconductors. However, very few imide-functionalized conjugated polymers have been reported in the literature. The body of this dissertation focuses on the synthesis, structure-property and device studies of imide-functionalized conjugated polymers. Reasons for choosing arylene imides as polymer building blocks include: a) they impart low-lying LUMOs to polymers, allowing band-gap engineering through choice of comonomers with variable electron-donating ability; b) imide-nitrogens provide points to attach side chains to manipulate solubility and solid-state packing; c) they are easily prepared. Structure-property studies include electrochemical measurements, UV-Vis absorption spectroscopy, differential scanning calorimetry (DSC), x-ray diffraction, and in some cases evaluation as active components in field-effect transistors (OFETs) and photovoltaic devices (PVDs). The published method to synthesize 3,6-dibromo-pyromellitic bisimides (PMBI) was streamlined and poly(phenylene ethynylene)s (PPEs) with variable band gaps were prepared from them (Chapter 2). As noted in all the chapters, electrochemical and optical measurements reveal that the LUMO of the polymers is indeed dictated by the arylene imide, while the HOMO, and therefore the optical energy gap is controlled through varying the electron donor monomer. Intramolecular hydrogen bonding was employed for increasing backbone coplanarity and therefore the polymer could have higher conjugation. One of these polymers demonstrated the narrowest band gap (1.50 eV) for any published PPE. Chapter 3 describes the first published conjugated copolymers from naphthalene bisimides (NBI), here using thiophene-based comonomers as donor units. Polymers with high molecular weight and decent solubility were obtained by choosing appropriate side chains. The optical energy gaps could be tuned across the visible and into the near IR. Preliminary OFET studies revealed electron mobility as high as ~0.01 cm2/Vs. One low band gap polymer provided OFETs with electron mobility of ~0.04 cm2/Vs and hole mobility of ~0.003 cm2/Vs, which is also among the highest mobilities of ambipolar polymeric semiconductors. Using the same approach as in Chapter 3, phthalimide-based monomers were incorporated into polymer backbones for developing new high performance p-type polymer semiconductors for OFETs and PVDs (Chapter 4). Some analogues based on benzothiadiazole, PMBI, and thiophene imides as acceptors were prepared for comparison. Again, high molecular weight, soluble polymers with band gaps spanning the visible and into the near IR were obtained. OFETs from one of the polymers yielded hole mobility ~0.3 cm2/Vs under ambient atmosphere without post-processing thermal annealing, which places it squarely within the state-of-the-art for conjugated polymers. Due to the high mobility and low band gap, this polymer also leads to PVDs with moderately good power conversion efficiency (PCE: ~2%)