Volume 39, Issue 2

The thermo-oxidative and thermal degradation kinetic parameters of polymethyl methacrylate-methacryloxyethyltrimethyl ammonium chloride/silica aerogel composites (PMMA-MTC/SA) were investigated in this paper and were compared with the thermal stability and thermal conductivity of different types of composites. As a composite with electrostatic interaction, the thermo-oxidative and thermal degradation activation energies ( E ) of PMMA-MTC/SA were 173.97 and 188.05 kJ/mol, respectively. The results indicated that the electrostatic interaction could indeed enhance the thermal stability of silica/polymethyl methacrylate composites on the premise of good mechanical properties and heat insulation performance. It is of great significance for the further development of silica-based thermal insulation composites.

Poly(vinyl chloride) (PVC) plastisols are widely used in the production of flexible PVC foams. In this study, we investigated the evolution of the complex viscosity of PVC plastisol by dynamic oscillatory tests, the storage modulus of the PVC compound by dynamic mechanical analysis, and the thermal behavior including the decomposition of three chemical blowing agents (CBAs), namely, azodicarbonamide, 4,4′-oxybis(benzenesulfonyl hydrazide), and sodium bicarbonate, by differential scanning calorimetry. Furthermore, the morphology and quality of the foams obtained from the corresponding plastisols were characterized by scanning electron microscopy. The results indicated that the onset decomposition temperature T2(5%) of a CBA in plastisol is the most critical indicator of the foam quality. The temperature difference corresponding to [T2(5%) – Tη max ] was also proved to be another important parameter. When T2(5%) is within the optimum temperature range of a PVC plastisol, the bigger the [T2(5%) – Tη max ] difference, the better the quality of the foams.

Study of the crystallization kinetics is particularly necessary for the analysis and design of processing operations, especially the non-isothermal crystallization behavior, which is due to the fact that most practical processing techniques are carried out under non-isothermal conditions. The non-isothermal crystallization behaviors of polyamide 6 (PA6) and PA6/high-density polyethylene/maleic anhydride/2,5-dimethyl-2,5-di( tert -butylperoxy)hexane (PA6/HDPE/MAH/L-101) composites were investigated by differential scanning calorimetry (DSC). The crystallization kinetics under non-isothermal condition was analyzed by the Jeziorny and Mo equations, and the activation energy was determined by the Kissinger and Takhor methods. The crystal structure and morphology were analyzed by wide-angle X-ray diffraction (WXRD) and polarized optical microscopy (POM). The results indicate that PA6/HDPE/MAH/L-101 has higher crystallization temperature and crystallization rate, which is explained as due to its heterogeneous nuclei.

Biodegradable polymer/bioceramic composite scaffolds can overcome the limitations of conventional ceramic bone substitutes, such as brittleness and difficulty in shaping. To better mimic the mineral components and microstructure of natural bone, a novel nano-hydroxyapatite (nHAp)–chitosan composite scaffold including gelatin and polymer (poly(lactic acid)) with high porosity was developed using a sol-gel method and subsequently lyophilized for efficient bone tissue engineering. The nanocrystalline structure of hydroxyapatite was observed using X-ray diffraction analysis and the composite showed crystallinity due to the presence of nHAp. The pore diameter of the composite containing 5% nHAp was found to be 125 μm, while the composites with 10%, 15%, and 20% nHAp revealed a smaller pore size in the range of 15–28 μm. The highest compressive strength of 5.5 MPa was observed for the 10% nHAp-containing scaffold, whereas thermogravimetric analysis showed 90%–94% degradation at a temperature of 600°C, which demonstrated its excellent thermal stability. Antibacterial and cytotoxicity test results revealed that the composite is resistant toward microbial attack and has low sensitivity in cytotoxicity. The compressive strength data suggests that the composite does not have enough strength as that of human compact bone; however, the highly porous structure as observed in scanning electron microscopy makes it possible for use as an excellent substrate in the spongy bone of humans.

A unique technology for producing thermoplastic vulcanizate (TPV) has been developed using an intermeshing-type internal mixer (ITM). TPV produced by the ITM was compared with that produced using a co-rotating twin screw extruder (Co-TSE) to assess the former’s commercial possibilities. TPV, originating from ethylene-propylene-diene monomer (EPDM) and polypropylene (PP), was produced by both machines with equal filled volumes, same shear rate, and same specific mechanical energy. Results indicate that ITMs can be used to produce TPV with mechanical properties comparable to those of TPV produced by Co-TSE. TPV can be produced with a lower shear rate with ITM compared to Co-TSE. A long residence time can be maintained in the mixing chamber of the ITM, allowing high conversion of the cross-linking reaction and resulting in better elastic recovery properties due to the higher cross-linking density. However, this resulted in higher viscosity of TPV produced by ITM.

Ethanol recovery via pervaporation is greatly influenced by membrane separation performance, which can be enhanced by adding hydrophobic fillers such as silicalite-1. Silicalite-1 was prepared by controlling the gel molar composition in hydrothermal synthesis, and it was incorporated into a polydimethylsiloxane (PDMS) membrane on Teflon. The silicalite-1 Si-O-Si structures interacted with the -Si(CH 3 ) 2 -O- backbone of the PDMS chain. The thermal gravimetric analysis results showed that the silicalite-1 improved the thermal stability and raised the initial decomposition temperature from 405°C to 450–470°C. Increasing silicalite-1 content from 5 to 20 wt% enhanced the relative ethanol/water swelling from 1.33% to 1.52% and advanced the contact angle from 112.6° to 138.6°. Addition of 20 wt% silicalite-1 improved the separation factor in broth from 2.55 to 5.56. When using 20 wt% silicalite-1/PDMS membrane and replacing the ethanol solution with broth, fouling reduced the flux from 597 to 482 g m −2 h −1 , but the broth composite increased the separation factor from 3.14 to 5.56. The overall pervaporation separation index with a santol broth of the 20 wt% silicalite-1/PDMS and commercial PDMS membranes were 2199 and 2110. The prepared membranes had similar overall performance as a commercial membrane.

Antistatic fibers or conductive fibers can be obtained from formation of a metal conductive layer, for example silver, on the surface of polymeric fibers through a redox reaction. However, in the process of fabricating silver-polymer conductive fibers, the binding force between silver and the polymeric fiber matrix is too weak and the poor weather resistance greatly affects the performance of the conductive fibers. This work aims to synthesize composite conductive layers of polyaniline (PANi)-silver coated on polyester fibers to prepare conductive polymeric fibers, in order to improve the combining ability between the conductive layers and the fiber matrix. The morphology, thermostability, mechanical properties, washing resistance and corrosion resistance of the resultant fibers obtained from different synthesis conditions were characterized. Batch experimental results showed that the concentration of the reagent and the reaction time could affect the resistance of the PANi-silver coated conductive fibers. The results also demonstrated that the PANi-silver composite conductive fibers have better properties than those of the silver-polymer conductive fibers.

The present study attempted to modify the surface of polymeric membranes by mixing 2-(perfluoroalkyl)ethanol with polyethersulfone to improve the hydrophobicity of the membrane. The characteristics of the surface-modified membrane were examined by using the contact angle, liquid entry pressure (LEP w ), X-ray photoelectron spectroscopy spectra, and scanning electron microscopy measurements. The modified membrane was tested for SO 2 absorption. The surface contact angle and LEP w values increased by the addition of fluoroalcohol. The fluorine/carbon atomic ratio decreased with increasing evaporation period. The modified membrane was utilized for the absorption of SO 2 from the simulated flue gas in alkaline medium (0.5 m NaOH solution). The SO 2 removal efficiency slightly decreased probably due to the transformation of the finger-like structure into a sponge-like structure, and the increase in the membrane resistance. The SO 2 absorption rate also increased as the gas flow rate increased.

The aim of this study is to analyze the effect of natural additive incorporation on processing nanocomposites and their effect on the functional characteristics of nanocomposites such as water uptake characteristics, drug adsorption and dissolution behaviors. Chitosan and montmorillonite were processed with olive oil and glycerin natural additives. In order to compare the processing results, the structure and the morphology of the polymer nanocomposites were examined by using infrared spectra, X-ray diffractograms and electron microscope images. Processing with nontoxic and healthful olive oil as a hydrophobizing agent overcame the high water uptake properties of the polymer nanocomposites and eliminated the use of other expensive chemicals. The nanocomposites without additives adsorbed the highest amounts of methylene blue at equilibrium. In vitamin B12 dissolution studies, not only the additives but also the reinforcement affected the results. Obviously, it can be seen that both the natural additive types and the reinforcement modification effects governed the drug adsorption and dissolution behaviors of the new tailored polymer nanocomposites. Moreover, the additives also improved the processing and handling abilities of these polymer nanocomposites. According to the results, these nanocomposites are promising candidates for medical applications like as a carrier for drug delivery and for skin treatment studies.

Dissolution of poorly water-soluble active pharmaceutical ingredients (APIs) in polymeric melts plays an important role in the manufacturing of solid dispersions and solid solutions. The understanding of the dissolution is essential for selecting the processing equipment, the operating conditions, and the polymer excipients. The methodology presented in this work for ketoprofen (KTO) and polymer excipients serves as a screening process to select the best API-polymer formulation for hot melt extrusion (HME) to target a specific release profile. KTO dispersion within the polymer was characterized by differential scanning calorimetry (DSC), X-ray diffraction (XRD), and dissolution tests. Thermal characterization shows that a single phase amorphous solid solution (one glass transition temperature [T g ]) was achieved under the HME processing conditions and screw configuration; and with the combination of polymer excipients, an extended release profile of KTO was accomplished, releasing 100% of KTO in 24 h.

The additive manufacturing process of the laser sintering of polymers (LS) allows the production of complex parts right from CAD data. However, the manufactured parts often show dimensional inaccuracies. In order to fundamentally determine the influencing parameters on the accuracy of LS parts, a hatching specimen, a layer-specimen and defined part geometries are manufactured and subsequently measured. These, combined with a theoretical observation of the layer wise geometry buildup, are used to determine the fundamental portions of the development of dimensions in building direction (z-direction). The results indicated a defined powder adhesion height at the top and the bottom of a melted layer, along with the dependency of melt depth and the hatch number for small structures. Depending on the nominal heights of an LS part, either an oversize or undersize was detected.