A series of bio-based hydrophobically modified isosorbide dimethacrylates, with para-, meta-, and ortho- benzoate aromatic spacers (ISBGBMA), are synthesized, characterized, and evaluated as potential dental restorative resins. The new monomers, isosorbide 2,5-bis(4-glyceryloxybenzoate) dimethacrylate (ISB4GBMA), isosorbide 2,5-bis(3-glyceryloxybenzoate) dimethacrylate (ISB3GBMA), and isosorbide 2,5-bis(2-glyceryloxybenzoate) dimethacrylate (ISB2GBMA), are mixed with triethylene glycol dimethacrylate (TEGDMA) and photopolymerized. The resulting polymers are evaluated for the degree of monomeric conversion, polymerization shrinkage, water sorption, glass transition temperature, and flexural strength. Isosorbide glycerolate dimethacrylate (ISDGMA) is synthesized, and Bisphenol A glycerolate dimethacrylate (BisGMA) is prepared, and both are evaluated as a reference. Poly(ISBGBMA/TEGDMA) series shows lower water sorption (39–44 µg/mm3) over Poly(ISDGMA/TEGDMA) (73 µg/mm3) but higher than Poly(BisGMA/TEGDMA) (26 µg/mm3). Flexural strength is higher for Poly(ISBGBMA/TEGDMA) series (37–45 MPa) over Poly(ISDGMA/TEGDMA) (10 MPa) and less than Poly(BisGMA/TEGDMA) (53 MPa) after immersion in phosphate-buffered saline (DPBS) for 24 h. Poly(ISB2GBMA/TEGDMA) has the highest glass transition temperature at 85 °C, and its monomeric mixture has the lowest viscosity at 0.62 Pa·s, among the (ISBGBMA/TEGDMA) polymers and monomer mixtures. Collectively, this data suggests that the ortho ISBGBMA monomer is a potential bio-based, BPA-free replacement for BisGMA, and could be the focus for future study.

The purpose of this discussion of fiber process–structure–property relationships is to illustrate the power of thermal analysis (TA) in the understanding and characterization of the complex processing history that is reflected in the nano–micro–macro structures of fibers, as well as the key structural and property parameters that define fiber performance. What is emphasized is the relationship between process conditions, fiber structure formation, and TA techniques. While the examples given relate to specific synthetic fibers with diameters of microns to a few tens of microns, the structure of all fibers (high-aspect-ratio materials of more or less circular cross section) will have similar features, and the relationship of morphology to properties is independent of formation conditions.

A model was developed to describe the nitration of cellulose in mixed acids used in the production of military grade nitrocellulose. Acid dissociation, swelling, diffusion, and chemical reaction were considered to model the nitration of industrially important cellulose materials for given reaction times and conditions. This model is supported by experimental work conducted to measure the dynamics of swelling and diffusion in wood pulp slivers, and the model was validated using the results of lab-scale nitration reactions. Microcomputed tomography was also used to perform a structural analysis of wood pulp slivers that were cut on industrial, rotary cutting machines to evaluate features that may influence the reactivity of these materials.

This figure by Piyush Modak and colleagues shows a patented porous architecture (20 x magnification) formed by a dynamic Schiff base network between acrylated chitosan (aCHN) & oxidized dextran (oDEX). This aCHN-oDEX network is a tunable, platform technology with various medical applications. Schiff base bonds in this network are mobile and reversible allowing additional Schiff base bonds to form over time, leading to a lower energy state and densification. In addition, the network shrinks, even when completely immersed in physiological solution, instead of swelling. And the shrinkage allows the 3D network to be used in enclosed structures such as the brain and spine. DOI: 10.1002/app.49756

Thermomechanical analysis (TMA) is one of the most important thermal analysis techniques. TMA and thermodilatometry measure some dimension as a function of temperature. The difference between them is that thermodilatometry measures the dimensional changes when negligible load is applied to the sample, while in TMA the load may be significant. TMA for fibers is a frequently used thermal analysis technique, because it can measure the thermal shrinkage and shrinkage force when the temperature is being raised. In this chapter the comparison of shrinkage force is given for drawn, heat set and relaxed fibers, and the origin of shrinkage force is explained. Fibers in most cases are characterized by the coefficient of linear thermal expansion measured in the fiber axis direction. The use of the newest TMA technique, modulated temperature TMA is presented and it is shown how to use the Reversing Dimension Change for characterizing shallow and broad glass transitions.

Early in the development of polymer science, Prof. H. Mark suggested that the tensile modulus of polymers should correlate with both the chemical and physical structures of the macromolecule. It was further recognized that maximum property levels would be achieved when all of the molecular chain backbone bonds of the polymer were lined up in the direction of measurement. Such an extended chain morphology has been demonstrated with gel spun polyethylene and with nematogenic polyamides and polyesters. Only main-chain liquid crystalline polymers (LCPs) exhibiting nematic behavior in the fluid state have found fiber applications. All of the LCPs are composed of stiff, highly aromatic monomers and are characterized by domains of high local orientation in the solid state (orientation function >0.95). If processed into fibers, the locally oriented domains are transformed into a single domain of high global molecular orientation parallel to the fiber direction. The thermal analysis literature, associated with lyotropic and thermotropic LCP fibers, is not extensive and work through the first decade of the 21st century and is well summarized in the books edited by Turi and by Menczel and Prime. In this chapter, the materials science of LCP fibers is reviewed, the recent application of TA techniques to LCP fibers is summarized, and the utility and impact of thermal analysis techniques in the understanding of LCP process–structure–property relations are discussed in detail.

In this study, we utilized the reversible property of aqueous Schiff bases to design a dynamic three-dimensional (3D) network. Two derivatized polysaccharides-acrylated chitosan (aCHN) and oxidized dextran (oDEX)-form a 3D network rapidly (<10 s) in situ without the use of external crosslinking agents. Reversible Schiff base (-N(sic)C-) pairs are formed between the amines of aCHN and aldehydes of oDEX. These bonds are mobile and reversible, allowing the network to form additional bonds, leading to lower energy state and densification. In the presence of a primary organic amine, the network dissolves completely, demonstrating network reversibility. The network has strong cohesion (85 +/- 7 mmHg) and adhesion (0.017 +/- 0.003 MPa) strengths. Rheological examination of the network demonstrates that both elastic storage (G') and viscous loss (G") moduli do not plateau but keep increasing over time. The network shrinks continuously over time, expelling fluid even when completely immersed in physiological solution, in contrast with conventional crosslinked networks that imbibe water and swell. Both rheology and shrinkage demonstrate the dynamic nature of the aCHN-oDEX networks. The dynamic nature of these networks is tunable and the properties of gelation, rheology, cohesion, adhesion, and densification can be modulated depending on the application of interest.

ABSTRACTNatural polysaccharides like chitosan and dextran have garnered considerable interest in biomedical applications due to their biocompatibility, biodegradability, and nontoxicity. Nonetheless, the development of a reproducible class of medical devices from these materials is challenging and has had limited success. Chitosan and dextran are inherently variable and synthesis using these materials is prone to inconsistencies. In this study, we put forward a robust product development regimen that allows these natural materials to be developed into a reproducible class of biomaterials. First, an array of validated characterization methods (Proton Nuclear Magnetic Resonance, titrations, Ultraviolet spectroscopy, Size Exclusion Chromatography—Multi‐Angle Light Scattering, Size Exclusion Chromatography—Refractive Index, and proprietary methods) were developed that allowed rigorous specifications to be set for unprocessed chitosan and dextran, chitosan and dextran intermediates, and chemically modified materials—acrylated chitosan (aCHN) and oxidized dextran (oDEX). Second, a robust and reproducible synthesis scheme involving various in‐process controls was developed to chemically modify the unprocessed polysaccharides. Third, purification methods to remove byproducts and low‐molecular‐weight impurities for both aCHN and oDEX were developed. The study presents a viable strategy for converting variable, natural materials into a reproducible class of biomaterials that can be applied in various biomedical applications. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020, 137, 48454.

A model has been developed to describe the reaction kinetics of single cellulose fibers (SCFs) in mixtures of nitric acid, sulfuric acid, and water during the production of highly nitrated nitrocellulose. Experiments were performed to provide insight into factors affecting the rate and extent of reaction for the nitration of wood-pulp-derived cellulose fibers in mixed acids and to provide kinetic data for model evaluation and kinetic parameter estimation. This work provided considerable information regarding the nature of the chemical reaction, and demonstrated that fiber properties do not play a significant role in the reaction kinetics or extent of reaction. This finding is particularly important because it allows for much broader range of wood pulps to be considered for industrial-scale nitration than have historically been used. A semiempirical kinetic model was developed to describe the conversion of cellulose to nitrocellulose as an equilibrium controlled reaction using these results. This kinetic model yielded excellent agreement with experimental results over the entire range of temperatures, fiber types, and reaction times studied.

A multi-scale analysis, at the mu m -> nm -> angstrom-scale on the influence of thermal treatment on the microstructure of the thermotropic polymer based on 60 mol% (1,4)-hydroxybenzoic acid (B), 5 mol% (2,6)-hydroxynaphthoic acid (N), 17.5 mol% terephthalic acid (T) and 17.5 mol% biphenol (BP) -named COTBP- was carried out. Extruded tapes 30 mu m thick were heat treated at 300 degrees C for up to 300 min. Wide-angle X-ray scattering of asextruded tapes revealed high macromolecular alignment. Small-angle X-ray scattering exhibited diamond-shaped diffuse scattering along the equatorial axis and, strikingly, meridional scattering revealed long-range order of ca. 43.9 nm periodicity. Heat treatment reduced surface roughness, increased the birefringence, and sharpened the meridional and main interchain reflections indicating an increase of crystallinity, molecular register and alignment. On the other hand, SAXS intensity decreased in 2 theta and became azimuthally narrower evidencing lateral compression of scattering features. The width of scattering objects decreased from 8.7 to 6.6 nm, whereas their length increased from 20.9 to 22.8 nm, and the misorientation angle B. decreased from 2.1 degrees to 0.5 degrees. Because heat treatment was carried out without applied tension, the results also revealed a self-reinforcing effect. The structural re-organization correlated with significant increase of thermal properties, i.e. the changes relative to as-extruded tape of degradation and melting temperatures were Delta T-dec similar to 20 K, Delta T(s -> n)75 K, and the change of Young's modulus was Delta E similar to 50 GPa.

Collagen fibers form the structural scaffolds of vertebrate tissues that store elastic energy, facilitate joint movement, and dissipate excess energy upon completion of joint movement. The purpose of this chapter is to discuss the molecular, microfibrillar and fibrillar structures of collagen fibers and the mechanism by which energy is stored, transmitted, and dissipated. The ability of collagen fibers to prevent premature mechanical failure of vertebrate tissues is also examined as well as the failure mechanisms of collagen fibers.

The discovery of electric fields in biological tissues has led to efforts in developing technologies utilizing electrical stimulation for therapeutic applications. Native tissues, such as cartilage and bone, exhibit piezoelectric behavior, wherein electrical activity can be generated due to mechanical deformation. Yet, the use of piezoelectric materials have largely been unexplored as a potential strategy in tissue engineering, wherein a piezoelectric biomaterial acts as a scaffold to promote cell behavior and the formation of large tissues. Here we show, for the first time, that piezoelectric materials can be fabricated into flexible, three-dimensional fibrous scaffolds and can be used to stimulate human mesenchymal stem cell differentiation and corresponding extracellular matrix/tissue formation in physiological loading conditions. Piezoelectric scaffolds that exhibit low voltage output, or streaming potential, promoted chondrogenic differentiation and piezoelectric scaffolds with a high voltage output promoted osteogenic differentiation. Electromechanical stimulus promoted greater differentiation than mechanical loading alone. Results demonstrate the additive effect of electromechanical stimulus on stem cell differentiation, which is an important design consideration for tissue engineering scaffolds. Piezoelectric, smart materials are attractive as scaffolds for regenerative medicine strategies due to their inherent electrical properties without the need for external power sources for electrical stimulation.

Thermally induced Angstrom and nanometer-scale reorganization in thermotropic liquid crystalline polymer based on (1,4)-hydroxybenzoic acid (B) and (2,6)-hydroxynaphthoic acid (N) was investigated by simultaneous wide-angle and small-angle X-ray scattering (SAXS, respectively). Extruded tapes 50 mu m thick were annealed at 240 degrees C under dry air conditions. The as-received tape exhibited fiber-like structure with crystalline order, whereas the SAXS patterns exhibited diamond-shaped diffuse scattering elongated along the equatorial axis elucidating nanovoid morphology oriented along the extrusion axis. Guinier analyses showed that the radius of gyration R-g of nanovoids were ca. 17 nm along the extrusion axis. Heat treatment produced a sharpening of the 002 meridional reflection and the 110 equatorial reflection suggesting an improvement of molecular register and packing. The molecular alignment, as quantified by the order parameter (P) over bar (2), increased as well as the degree of crystallinity chi. On the other hand, SAXS intensity along the equatorial axis decreased evidencing reduction of R-g, i.e. lateral compression of the nanovoids and better molecular packing. Thermal treatment increased the thermal stability and the uniaxial tensile Young's modulus, Delta E, along extrusion axis. However, the tapes exhibited microhardness anisotropy and the indentation anisotropy,.H, gradually decreased suggesting reduction of elastic recovery in the molecular chain direction. Scanning electron microscopy evidenced an outer skin with an internal layered morphology that transformed into sheet-like morphology with meandering fibrils. This investigation evidenced microstructure and morphology reorganization correlating with improved thermal and mechanical properties. Copyright (C) 2015 John Wiley & Sons, Ltd.

Jet fuels are stabilized with polymers assembling in solution [Also see Report by Wei et al. ]