Synthesis and characterization of two-stage curing reactive bio-based polymers

Two-stage curing reactive bio-based polymers network namely, poly(octanediol-co-dodecanedioate-co-citrate-co-itaconate) (PODCI) were successfully synthesized using 1,8-octanediol, citric acid, itaconic acid and 1,12-dodecanedioic acid. In the first curing stage, a prepolymer of PODCI was thermally crosslinked. At a later time, a second curing was completed thru photo-initiated free-radical polymerization. Here, we discovered that permanent shape of the thermally crosslinked PODCI was successfully reconfigured by application of second stage curing. The molar ratio of itaconic acid (IA) to citric acid (CA) and time of photo-curing was varied. Based on XRD analysis, the polymer crystallinity of the bio-based polymer decreased with time of photo-curing. The swelling ratio of bio-based polymer decreased from 2750 % to 250 % as soon as completion of second stage curing. PODCI existed as a semi-crystalline polymer with a melting transition temperature of 40.2 ℃. Also, PODCI exhibited excellent shape memory properties with shape recovery by nearly 100%

Water transport properties of boron nitride nanosheets incorporated thin film nanocomposite membrane for salt removal

This work has focused on the fabrication of thin film composite (TFC) and thin film nanocomposite (TFN) membranes for reverse osmosis (RO) application. Raw boron nitride (BN) and chemically activated boron nitride (A-BN) were used as nanofillers in polysulfone support layer and trimesoyl chloride (TMC) to improve the membrane performance. Different concentrations of BN and A-BN (ranging from 0 to 1 wt %) were added to the polysulfone (PSf) microporous support and polyamide layer was formed on top of PSf support through interfacial polymerization of 1,3-Phenylendiamine and trimesoyl chloride. The fabricated TFN membranes were characterized in terms of membranes structure, contact angle, separation properties, as well as RO performance. According to AFM and SEM images, TFN membranes showed larger average pore size and higher surface roughness as compared with TFC membrane. Thus, TFN membrane showed higher pure water flux but lower NaCl rejection. The addition of BN led to increase in pore size of membrane without increase the selectivity of membrane. The addition of both BN and A-BN into polyamide layer does not aid to improve the properties of membrane. In conclusion, BN nanoparticles showed the potential to be used as nanofillers that aid in formation of larger pore size

Structural and characterization studies of insoluble Thai Bombyx mori silk fibroin films

Bombyx Mori fiber consists of two major proteins which are fibroin and sericin. The silk fibroin (SF) is the core structural protein of silk fiber. SF protein structures comprise of primary and secondary structures; where the primary structure contains series of amino acid and secondary structure with Silk I refers to the water-soluble and Silk II, high β sheet extent which is insoluble. This study was conducted to compare the structural and characterization of insoluble Thai Bombyx Mori SF with different types of post-treatement. Thai silk cocoons, which were degummed and dissolved in 9.3 M LiBr solution at 60 °C. The obtained SF solutions were dialyzed and purified. SF films were prepared by solution casting and immersing in methanol and ethanol, followed by water annealing in water saturated vacuum. Post-treatment was purposely done to regenerate and induce of the β sheet structure to enhance the insolubilities and the stabilities properties of the SF films. The SF films structural conformation, characterization and thermal stability were characterized. Attenuated total reflectance-Fourier transformed infrared spectroscopy (ATR-FTIR) showed that SF films were presented in a more stable form after ethanol post treatment, which also supporting by X-ray diffraction (XRD) analysis which indicated the tendency to higher structural organization. Thermal analysis resutls showed that SF was thermally stable and improved after post treatment. The contact angle of post treated SF increased the hydrophobicity of the films. The thai SF films could be the promising candidate for applications in tissue regeneration, optical devices, and flexible electronic displays with the possibility to control the SF structure and properties

Mechanical and thermal properties of biodegradable hydroxyapatite/poly(sorbitol sebacate malate) composites

In this project, novel hydroxyapatite (HAp)/poly(sorbitol sebacate malate) (PSSM) composites for potential application in soft tissue engineering were developed. The composites consist of the biodegradable polyester prepared from sorbitol, sebacic acid, malic acid and various amount of HAp (5, 10, and 15 wt%). Effects of different weight percents of HAp on the properties of the composites were studied. Fourier transform infrared spectroscopy was performed to analyze chemical interactions between HAp/PSSM. Tensile tests and differential scanning calorimetry were conducted to evaluate the mechanical and thermal properties of HAp/PSSM composites. Tensile testing on HAp/PSSM composites showed that their mechanical properties improved with increasing concentration of HAp. The Young's modulus and tensile strength of the composites ranged from 16.20±1.73 to 23.96±2.56 MPa and 626.96±81.04 to 1,026.46±105.12 MPa, respectively. The glass transition temperature of all samples was slightly higher than room temperatur

Tunable topological phase transition in soft Rayleigh beam system with imperfect interfaces

Acoustic metamaterials, particularly the topological insulators, exhibit exceptional wave characteristics that have sparked considerable research interest. The study of imperfect interfaces affect is of significant importance for the modeling of wave propagation behavior in topological insulators. This paper models a soft Rayleigh beam system with imperfect interfaces, and investigates its topological phase transition process tuned by mechanical loadings. The model reveals that the topological phase transition process can be observed by modifying the distance between imperfect interfaces in the system. When a uniaxial stretch is applied, the topological phase transition points for longitudinal waves decrease within a limited frequency range, while they increase within a larger frequency scope for transverse waves. Enhancing the rigidity of the imperfect interfaces also enables shifting of the topological phase transition point within a broader frequency range for longitudinal waves and a confined range for transverse waves. The transition of topologically protected interface modes in the transmission performance of a twenty-cell system is verified, which include altering frequencies, switching from interface mode to edge mode. Overall, this study provides a new approach and guideline for controlling topological phase transition in composite and soft phononic crystal systems.Comment: 39 pages,8 figure

Inferior market performance of initial public offerings issued by family firms : myth or reality?

This study sought to investigate whether the notion that family firms underperform non-family firms in terms of their stock price is valid or groundless, with emphasis on Chinese family firms that form the majority of local enterprises in Singapore. Analysis of the information was conducted on both the short- and long-run

Kappa-carrageenan/halloysite nanocomposite hydrogels as potential drug delivery systems

Novel kappa-carrageenan (Kc)/halloysite nanotube (HNT) nanocomposite hydrogels were synthesized via physical crosslinking for the gastro-intestinal tract (GIT) release. The influence of HNT nanoparticle content on Kc/HNT hydrogel properties such as thermal, swelling, drug loading and in vitro release was examined. Thermal results revealed that the incorporation of HNT nanoparticles enhanced the thermal stability of the nanocomposite hydrogels. Also, the nanocomposite hydrogels showed higher swelling, drug loading and release behavior compared to the pure Kc hydrogel. In vitro release from the Kc-HNT hydrogels exhibited that rhodamine B (RB), a cationic model drug, released higher than orange G (OG), an anionic model drug. RB in vitro release from the nanocomposite hydrogels reached to approximately 72%, while 54% of OG was released. Finally, in vitro cytotoxicity test revealed that both Kc and Kc-HNT hydrogels are biocompatible. Taking together, it was shown that Kc-HNT hydrogels may have a great potential applications in oral drug delivery systems

Controlling three-dimensional ice template via two-dimensional surface wetting

Directional freezing (DF) is a fast, scalable, and environmental friendly technique for fabricating monoliths with long- range oriented pores, which can be applied toward a wide variety of materials. However, the pore size is typically larg- er than 20 l m and cannot be spatially controlled, which prevent the technique from being used more widely. In this work, effect of wettability of the freezing substrate on the pore size of monolithic polyethylene glycol cryogels is studied. Smaller pores can be generated via more hydrophilic substrates, and tubular pores smaller 5 l m can be created using a poly(vinyl alcohol) coated copper substrate. A numerical fitting between water contact angle of the substrates and pore size is then obtained. Moreover, pore size can be locally varied duplicating wetting patterns of the substrates. The concept of using two dimensional patterns to build monoliths with three dimensional microstructures can probably be extended to other material systems. DF is an effecient and scalable processing method for fabricating materials with long-range oriented pores. However, the smallest pore feature size reported is around 20 m m, which is in many cases too large for application such as separation and catalysis. We show here, with exemplary cryogels, that both spatial control and feature size reduction (by one order of magnitude) can be realized in DF by controlling the wettability of the ice growth substrate

A novel poly(xylitol-co-ledodecanedioate)/hydroxyapatite composite with shape-memory behaviour

A novel shape-memory polymer, poly(xylitol-co-dodecanedioate) (PXDD) was developed and the effect of hydroxyapatite (HA) in PXDD/HA composites on the chemical interactions, shape-memory and crystallization behaviours was studied. FIR confirmed the formation of PXDD and also showed that the chemical structure did not change with the addition of HA. DSC and XRD revealed that the degree of crystallinity (X-c) of PXDD/HA composites improved in parallel to increasing HA content. The permanent shape is recovered with a precision of almost 100% as soon as the recovery temperature (T-rec=48 degrees C) is reached. The findings of the study showed that PXDD/HA composites have great potential as shape-memory implant in minimal invasive surgeries. (C) 2014 Elsevier B.V. All rights reserved

Polyol-based biodegradable polyesters: a short review

Catalyst-free thermal polyesterification has recently emerged as a potential strategy for designing biodegradable thermoset polymers, particularly polyol-based polyesters for biomedical applications. These thermoset polyesters are synthesized through polycondensation of polyol and polyacid without the presence of catalyst or solvents. The mechanical properties, degradation rates, crystallinity, hydrophilicity, and biocompatibility can be controlled by adjusting the monomer feed ratios and curing conditions. These polyesters often degrade via surface erosion that allows the polymers to maintain structural integrity throughout hydrolysis. Additionally, polyol-based polyesters demonstrated good biocompatibility as non-toxic catalysts and/or solvents involved in the reaction, and the monomers used are endogenous to human metabolism which can be resorbed and metabolized in various physiological pathways. This review summarizes the polyol-based biodegradable polyesters that were synthesized by catalyst-free polyesterification