Photodegradation of Poly(L‐lactic acid): Effects of Photosensitizer

Summary: Amorphous and crystallized poly(L ‐lactic acid) (PLLA‐A and PLLA‐C, respectively) films with different contents of N,N,N′,N′‐tetramethyl‐1,4‐phenylenediamine (TMPD) as a photosensitizer were prepared, and the effects of the addition of TMPD on the photodegradation of PLLA films were investigated. It was found that the addition of TMPD effectively enhanced the photodegradation of PLLA films and thereby decreased their molecular weight of PLLA films regardless of their crystallinity, and that PLLA films with different molecular weights can be prepared by the addition of different amounts of TMPD and subsequent UV irradiation. Too high contents of TMPD however caused the brittleness of PLLA films due to a large decrease in molecular weight. The PLLA chains in crystalline regions as well as those in amorphous regions are photodegradable even at an early stage, in marked contrast to their hydrolytic degradation, where the chains in the amorphous regions are selectively degraded. The basic changes in glass transition, cold crystallization, and melting temperatures (T_g, T_cc, and T_m, respectively) of PLLA films during UV irradiation can be ascribed to low‐temperature annealing effects; i.e., annealing‐induced stabilization in chain packing should have elevated T_g, and annealing‐induced formation of crystallite nuclei should have lowered T_cc and increased T_m. The exceptional large decreases in T_cc and T_m of UV‐irradiated PLLA‐A films and in T_g of UV‐irradiated PLLA‐C films at high TMPD contents are attributable to the large decrease in molecular weight, whereas the exceptional decrease in T_m of PLLA‐C films at high TMPD contents can be due to the folding surface structural change of crystalline regions or to the lattice disorder caused by molecular structural changes.

of PLLA‐A films before UV irradiation and after UV irradiation for 60 h as a function of TMPD content.     

Enzymatic degradation of poly(L‐lactic acid) fibers: Effects of small drawing

The enzymatic degradation of poly(L ‐lactic acid) (PLLA) fibers with different low draw ratios (1.0, 1.2, and 1.4 times) was investigated in tris‐HCl buffer solution (pH = 8.6) with proteinase K by the use of gravimetry, scanning electron microscopy (SEM), gel permeation chromatography (GPC), differential scanning calorimetry (DSC), and tensile testing. Surprisingly, even the small drawings (1.2 and 1.4 times) disturbed the proteinase K catalyzed enzymatic degradation of the PLLA fibers. This should have been because the enzyme could not attach to the extended (strained) chains in the amorphous regions of the uniaxially oriented PLLA fibers or could not catalyze the cleavage of the strained chains. The accumulation of crystalline residues formed as a result of selective cleavage, and removal of the amorphous chains was not observed, even for as‐spun PLLA fibers. This indicated the facile release of formed crystalline residues from the surface of the as‐spun PLLA fibers during enzymatic degradation. Such release may have been because the crystalline regions of the as‐spun PLLA fibers were oriented with their c axis parallel to the machine direction, as reported for biaxially oriented PLLA films. Gravimetry, SEM, and tensile testing could trace the enzymatic degradation of the PLLA fibers, although the enzymatic degradation of the PLLA fibers was untraceable by GPC and DSC. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 2064–2071, 2007     

Y-doped SrTiO3 based sulfur tolerant anode for solid oxide fuel cells

A solid oxide fuel cell (SOFC) anode with high sulfur tolerance was developed starting from a Y-doped SrTiO₃ (SYTO)-yttria stabilized zirconia (YSZ) porous electrode backbone, and infiltrated with nano-sized catalytic ceria and Ru. The size of the infiltrated particles on the SYTO-YSZ pore walls was 30–200 nm, and both infiltrated materials improved the performance of the SYTO-YSZ anode significantly. The infiltrated ceria covered most of the surface of the SYTO-YSZ pore walls, while Ru was dispersed as individual nano-particles. The performance and sulfur tolerance of a cathode supported cell with ceria- and Ru-infiltrated SYTO-YSZ anode was examined in humidified H₂ mixed with H₂S. The anode showed high sulfur tolerance in 10–40 ppm H₂S, and the cell exhibited a constant maximum power density 470 mW cm⁻² at 10 ppm H₂S, at 1073 K. At an applied current density 0.5 A cm⁻², the addition of 10 ppm H₂S to the H₂ fuel dropped the cell voltage slightly, from 0.79 to 0.78 V, but completely recovered quickly after the H₂S was stopped. The ceria- and Ru-infiltrated SYTO-YSZ anode showed much higher sulfur tolerance than conventional Ni-YSZ anodes.     

Diffusive permeability of ionic solutes in charged chitosan membrane

The permeabilities of three kinds of solutes with similar sizes such as anionic benzenesulfonic acid, neutral styrene glycol, and cationic theophylline in the chitosan membrane were investigated. The chitosan membrane becomes cationic below its pKa value. Benzenesulfonic acid showed the highest permeability, whereas theophylline showed the lowest, although these solutes have almost the same size. This can be explained by the electrostatic attraction or repulsion between the solute and the membrane instead of the size exclusion effect. The permeabilities of benzenesulfonic acid and theophylline increased and decreased, respectively, with the decrease of pH from 7.4 to 4.0 because of the increase of the charge density of the membrane. Thus, the selectivity of benzenesulfonic acid to theophylline increased and reached about 30 at pH 4.0, in contrast to the selectivity of nearly unity in poly(vinyl alcohol) (PVA) membrane. The partition coefficients for three solutes showed the similar tendencies to those in the permeabilities. Contrary to the results of the permeabilities, the partition coefficients increased with the increase of the degree of the crosslinking in the membrane. This is probably due to the increase of the electrostatic interaction between the solute and the membrane brought about by the smaller mesh size and also due to the increase of the bound water fraction in the membrane. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 397–404, 1999     

Porous biodegradable polyesters. I. Preparation of porous poly(L‐lactide) films by extraction of poly(ethylene oxide) from their blends

Porous poly(L ‐lactide) (PLLA) films were prepared by water extraction of poly(ethylene oxide) (PEO) from solution‐cast PLLA and PEO blend films. The dependence of blend ratio and molecular weight of PEO on the porosity and pore size of films was investigated by gravimetry and scanning electron microscopy. The film porosity and extracted weight ratio were in good agreement with the expected for porous films prepared using PEO of low molecular weight (M_w = 1 × 10³), but shifted to lower values than expected when high molecular weight PEO (M_w = 1 × 10⁵) was utilized. The maximum pore size was larger for porous films prepared from PEO having higher molecular weight, when compared at the same blending ratio of PLLA and PEO before water extraction. Differential scanning calorimetry of as‐cast PLLA and PEO blend films revealed that PLLA and PEO were phase‐separated at least after solvent evaporation. On the other hand, comparison of blend films before and after extraction suggested that a small amount of PEO was trapped in the amorphous region between PLLA crystallites even after water extraction and hindered PLLA crystallization during solvent evaporation. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 629–637, 2000     

Kinetic studies of thermally induced phase separation in polymer–diluent system

Thermally induced phase separation was studied by the light scattering in polypropylene/methyl salicylate system. Data could be well fitted with the linear Cahn theory for spinodal decomposition (SD) in the early stage of phase separation. Characteristic properties of the early stage of SD, such as an apparent diffusion coefficient and an interphase periodic distance, were obtained. The periodic distance ranged from 3 μm to 4 μm. The growth of the phase‐separated structure obeyed power‐law scaling in the later stage, and the structure factor could be scaled into a universal time‐independent form. Domain sizes obtained from the light‐scattering measurements were consistent with the optical microscope measurements. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 1028–1036, 2000     

Polydopamine-coated poly(vinylidene fluoride) membranes with high ultraviolet resistance and antifouling properties for a photocatalytic membrane reactor

We modified poly(vinylidene fluoride) (PVDF) membranes with a polydopamine (PDA) coating for photocatalytic membrane reactor application with appropriate UV resistance and studied the effects of the PDA coating conditions (i.e., coating time and dopamine concentration) and UV irradiation time on the modified PVDF membrane properties. The PVDF membrane that was surface-coated with the appropriate dopamine solution concentration and coating time played a key role in controlling the membrane properties and in protecting the modified membrane against UV radiation. The optimization of the coating condition not only completely protected the modified membrane from free-radical attack initiated through UV irradiation but also improved the membrane hydrophilicity, antifouling properties, filtration performance, and mechanical strength of the membrane. UV irradiation of the membrane that was surface-coated with a high-concentration dopamine solution for a long coating time resulted in a higher mechanical strength than that of the membrane without the application of UV irradiation. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47312.     

Physiological and psychological evaluations in low- and high-frequency noise using near-infrared spectroscopy

This study aims to evaluate physiological and psychological states using near infrared spectroscopy in noise environments with low or high frequencies. Our system assumes that noise affects brain activity in the frontal lobe. In order to evaluate the subject’s states in a noise environment, we constructed an experimental system that measures the subject’s states. The experimental method adopted here was borrowed from our previous studies. In the present study, we collected experimental data about the subject’s unpleasant or pleasant experiences by producing a noise environment with low and high frequencies. We conclude that noises with low or high frequencies affect our psychological states as well as brain activity in the frontal lobe.     

Non-destructive monitoring of creaming of oil-in-water emulsion-based formulations using magnetic resonance imaging

A non-destructive method for monitoring creaming of emulsion-based formulations is in great demand because it allows us to understand fully their instability mechanisms. This study was aimed at demonstrating the usefulness of magnetic resonance (MR) techniques, including MR imaging (MRI) and MR spectroscopy (MRS), for evaluating the physicochemical stability of emulsion-based formulations. Emulsions that are applicable as the base of practical skin creams were used as test samples. Substantial creaming was developed by centrifugation, which was then monitored by MRI. The creaming oil droplet layer and aqueous phase were clearly distinguished by quantitative MRI by measuring T₁ and the apparent diffusion coefficient. Components in a selected volume in the emulsions could be analyzed using MRS. Then, model emulsions having different hydrophilic–lipophilic balance (HLB) values were tested, and the optimal HLB value for a stable dispersion was determined. In addition, the MRI examination enables the detection of creaming occurring in a polyethylene tube, which is commonly used for commercial products, without losing any image quality. These findings strongly indicate that MR techniques are powerful tools to evaluate the physicochemical stability of emulsion-based formulations. This study will make a great contribution to the development and quality control of emulsion-based formulations.