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     

Porous biodegradable polyesters. II. Physical properties,morphology, and enzymatic and alkaline hydrolysis of porous poly(ϵ‐caprolactone) films

Porous poly(?‐caprolactone) (PCL) films were prepared by water extraction of poly(ethylene oxide) (PEO) from their solution‐cast phase‐separated blend films and the dependence of their blend ratio [X_PCL = PCL/(PEO + PCL)] and molecular weight of PEO on the porosity, pore size, crystallinity, crystalline thickness, mechanical properties, morphology, and enzymatic and alkaline hydrolysis of the porous PCL films were investigated. The film porosity or extracted weight ratio was in good agreement with the expected values, irrespective of X_PCL and molecular weight of PEO. The maximum pore size was larger for the porous films prepared using PEO having a lower molecular weight, compared with films prepared using PEO having a higher molecular weight at the same X_PCL. Differential scanning calorimetry of the porous PCL films revealed that their crystallinity and crystalline thickness were almost constant, regardless of X_PCL and molecular weight of PEO. The Young's modulus and tensile strength of the porous films decreased, whereas the elongation‐at‐break increased with decreasing X_PCL. The enzymatic and alkaline hydrolysis rates of the porous films increased with a decrease in X_PCL and an increase in the molecular weight of PEO. The porous PCL films having Young's modulus in the range of 2–24 kg/mm² and enzymatic hydrolysis rate in the range of one‐ to 20‐fold that of the nonporous PCL film could be prepared by altering X_PCL and the molecular weight of PEO. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 2281–2291, 2001     

Relationship between the structure and mechanical properties of polypropylene: Effects of the molecular weight and shear‐induced structure

A series of homopolymer polypropylenes (PPs), within a weight‐average molecular weight (M_w) range of 100–1600 kg/mol, were manufactured as dumbbell microspecimens. The effects of the molecular weight and shear‐induced crystallization on the mechanical properties and morphology were studied to gain a better understanding of the structure–property relationship. The results showed that the crystallinity decreased from 50 to 41% and the lamellar thickness increased as M_w increased. Tensile tests demonstrated that the stiffness and especially the tensile strength rose to extremely high values (Young's modulus = 2400 N/mm², stress at 30% strain = 120 N/mm²). Furthermore, the strain hardening effect was strongly affected by the lamellar thickness and highly oriented superstructures. Dynamic mechanical analysis demonstrated that the mobility of the molecular chains depended on M_w and on the lamellar thickness. In addition, the viscoelastic properties of unannealed and annealed samples indicated further the existence of shish‐kebab structures caused by shear‐induced crystallization during injection molding. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 519–533, 2007     

Films made from poly(vinyl alcohol‐co‐ethylene) and soluble biopolymers isolated from postharvest tomato plant

Blended films were obtained from polyvinyl alcohol‐co‐ethylene (EVOH) with 52 kDa weight average molecular weight (M_w) and three water soluble biopolymers isolated from exhausted tomato plants hydrolysates. Two biopolymers contained mainly polysaccharides and had 27 and 79 kDa M_w, respectively. The third contained mainly lignin‐like C moieties and had 392 kDa M_W. The films were fabricated with a biopolymer/EVOH w/w ratio ranging from 0.1 to 0.9. All blends had molecular weight and solubility which were substantially different from the starting materials. They were characterized for the chemical nature, and the thermal, rheological, and mechanical properties. Evidence of a chemical reaction between the biopolymers and EVOH was found. Generally, the films exhibited higher mechanical strength but lower strain at break then the neat EVOH. The best performing blended film was fabricated from the 27 kDa M_w polysaccharide. This contained less than 10% biopolymer. It exhibited 1043 MPa Young's modulus and 70% strain at break against 351 MPa modulus and 86% strain for neat EVOH. The results offer scope for investigating biopolymers sourced from other biowastes to understand more the reasons of the observed effects and exploit their full potential to modify or to replace synthetic polymers. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41935.     

壳聚糖分子量对酵母细胞固定化培养的影响

以海藻酸钠-壳聚糖微胶囊（AC微胶囊）为研究对象,以酵母细胞S.cerevisiae BY4741为细胞模型,分别考察了相同成膜反应时间和相同成膜厚度两种情况下,壳聚糖分子量对微囊膜膨胀行为、微囊内细胞增殖情况及微囊化细胞培养过程中细胞泄漏的影响规律。研究结果显示,在成膜反应时间相同的情况下,壳聚糖分子量越小,向海藻酸钙凝胶网络扩散越容易,交联成膜越厚,微胶囊膜越能耐受渗透压膨胀。但在控制相同膜厚的情况下,大分子量壳聚糖由于分子链长,与凝胶微球表面海藻酸钠分子的作用位点多,易纠结相邻海藻酸钠分子链形成更致密的络合交联,呈现更高的耐受渗透压膨胀的特性。AC微囊化细胞培养48 h后,小分子量壳聚糖充分成膜反应制备的AC微胶囊,虽然膨胀不显著,但由于膜结构占据了更多微胶囊体积,既缩小了酵母细胞的增殖空间,又极大增加了传质阻力,反而限制了细胞增殖。培养过程中,各组微胶囊均未发现明显的细胞泄漏现象。     

Effect of morphology on shear viscosity for binary blends of polycarbonate and polystyrene

The structure and rheological properties of binary blends of polycarbonate (PC) and polystyrene (PS) were investigated using various PS samples with different molecular weights, namely PS1k (M_w = 1,000), PS53k (M_w = 53,000), and PS240k (M_w = 240,000). The blends with PS53k and PS240k show phase-separated structures, whereas the blend with PS1k is miscible. The shear viscosity decreases greatly on addition of PS53k and PS240k, especially at high shear rates, which would be a great advantage at processing operations. Because the nonlinear response occurs in the small strain region for multilayered films of PC and PS240k, the origin of the significant viscosity drop for the phase-separated system is interfacial slippage at the phase boundary.     

Effect of molecular weight and molecular weight distribution on the rheological properties of aqueous poly(ethylene oxide) solution

The effect of the molecular weight and the molecular weight distribution on the rheological properties of aqueous poly(ethylene oxide) (PEO) solutions has been investigated with four PEO samples differing in their M_w, M_w/M_n and purity. The main result of this study is that the steady shear viscosity as well as the complex dynamic viscosity of the samples with broad molecular weight distribution greatly differed from the viscosities of the samples having a narrow molecular weight distribution. Furthermore, the samples with broad molecular weight distribution showed a distinct molecular weight dependent non-Newtonian behavior at increasing shear rates and frequencies. This behavior was not observed for the sample with a narrow molecular weight distribution. Both effects are mainly attributed to the influence of the high molecular weight fraction in the PEO samples of broad molecular weight distribution. The often reported degradation of PEO solutions was not observed within the time scale of our experiment.     

Casting solvent effect on crystallization behavior of poly(vinyl acetate)/poly(ethylene oxide) blends: DSC study

Poly(vinyl acetate) (PVAc)/poly(ethylene oxide) (PEO) blends were prepared by casting from either benzene or chloroform. The solvent effects on the crystallization behavior and thermodynamic properties of the blends were studied by the differential scanning calorimeter (DSC). Two grades of PEO with different molecular weights (PEO200 with M_w = 200,000 g/mol and PEO2 with M_n = 2000 g/mol) were used in this work. The thermal analysis revealed that the blends cast from either benzene or chloroform were miscible in the molten state. The crystallization of PEO in the benzene-cast blends was more easily suppressed than it was in the chloroform-cast blends. Furthermore, the benzene-cast blends showed a greater negative value of Flory-Huggins interaction parameter than those cast from chloroform in the PVAc/PEO200 poly-blend system. It was supposed that the benzene-cast blends had more homogeneous morphology. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 411–421, 1997     

Preparation and properties of polyurethane/benzyl amylose semi‐interpenetrating networks

A series of semi‐interpenetrating polymer networks (semi‐IPNs) films were prepared from 20 wt % of benzyl amylose (BA) of different M_w and castor oil‐based polyurethane (PU) in N,N‐dimethylformamide (DMF). The weight‐average molecular weight (M_w), and radii of gyration (<S²>_z^1/2) of benzyl amylose were determined by laser scattering measurement, and the results suggested BA was in a compact coil conformation in DMF. Furthermore, the properties and miscibility of the polyurethane/benzyl amylose (PUBA) films were studied by scanning electronic microscopy, differential scanning calorimetry, dynamic mechanical thermal analysis, ultraviolet–visible spectrophotometer, and tensile testing. The PUBA films possessed much higher optical transmittance and tensile strength than the pure PU film regardless of the molecular weight of BA, but lower values of elongation at break were observed. With decreasing of the BA M_w from 9.24 × 10⁵ to 2.69 × 10⁵, interestingly, the elongation at break of the films increased from 135 to 326%. This might be ascribed to the decrease of crosslinking density of PU networks and the enhancement in freedom of the molecular motion. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Effect of sonolysis on kinetics and physicochemical properties of treated chitosan

Low molecular weight chitosan with weight‐average molecular weight from 161 to 22,000Da were obtained by sonolysis. Optimal conditions for sonolysis were described. The influence of sonolysis condition and the molecular parameters of initial chitosan on the degradation rate and degradation rate constant were investigated in detail. Weight‐average molecular weight (M_w) and molecular weight dispersion (M_w/M_n) of samples were measured by gel permeation chromatography. The structure of degraded chitosan were characterized by Fourier transform infrared, X‐ray diffraction, and electrospray ionization mass spectrometry. For a given sonolysis time, the decrease in molecular weight has been found to be greatest at lowest reaction temperature and lowest chitosan concentration. Molecular weight of samples decreased exponentially with increasing sonication time at early stages. The action mode of ultrasound on the splitting of molecular chain of chitosan has been discussed. The degree of deacetylation of the main hydrolysis products almost unchanged compared with the initial chitosan. The decrease of molecular weight led to transformation of crystal structure but the chemical structures of residues were not modified. Ultrasonic treatment on chitosan is an alternative, safe method to prepare chitosan having different molecular weights, which are more suitable for biomedical and food applications. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Low molecular weight water‐soluble chitosans: Preparation with the aid of cellulase,characterization, and solubility

Preparation of water‐soluble chitosan (WSC) was made by treating partially N‐deacetylated chitosan with acetic anhydride in aqueous acetic acid. The optimal conditions of preparing WSC were determined on the basis of orthogonal tests. Low molecular weight WSC with broad molecular weight (600–1.5 kDa) were obtained by the depolymerization of WSC using cellulase at optimum condition of pH 4.5 and 60°C. The solubility of WSC in water and aqueous organic solvents was investigated in detail. Weight–average molecular weight (M_w) and molecular weight distribution (M_w/M_n) of samples were measured by gel permeation chromatography. The structure of WSC and its degraded products were characterized by XRD, FTIR, and MALDI‐TOF MS. The decrease of molecular weight led to transformation of crystal structure and the increase of solubility, but the chemical structures of residues were not modified compared to WSC, which was not hydrolyzed. The solubility of the WSC in water and aqueous organic solvents increased with the decrease of molecular weight. The solubility of the WSC with low molecular weight was rather high even in aqueous dimethylacetamide and dimethylsulfoxide. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 1098–1105, 2006     

Synthesis of nonionic flocculants by gamma irradiation of mixtures of polyacrylamide and poly(ethylene oxide)

The synthesis of polyacrylamide (PAM) graft poly(ethylene oxide) (PEO) has been investigated and the reaction conditions were varied by gamma irradiation to optimize polystyrene latex flocculation by the copolymers. The effects of the gamma ray dosage, the PEO chain length, the ratio of PEO to PAM, and the crosslinking degree of copolymer were studied. The most effective flocculant was obtained by exposing a mixture of 1.2 wt % PAM (M_w = 5 × 10⁶) and 0.94 wt % PEO (M_w = 5000) to 816 krad of gamma radiation. The resulting copolymer contained 24 wt % PEO. Crosslinking to give insoluble gels was an undesirable side reaction increased with γ-ray dose and decreased with PEO addition. The most effective flocculants contained more than 15 wt % PEO with little crosslinking. The grafting behavior of triblock copolymer, poly(ethylene oxide)-b-poly(propylene oxide)-b-poly(ethylene oxide) (E_mP_nE_m, where m and n are oxyethylene and oxypropylene unit, respectively), onto PAM by gamma radiation was also studied; grafting occurred but effective flocculants were not obtained. © 1994 John Wiley & Sons, Inc.     

Effects of the molecular weight on the properties of thermoplastics prepared from soy protein isolate

Commercial soy protein isolate (SPI) was fractionated into four fractions by an acidifying method from pH 5.7 to 4.5 with 2M HCl. A mixture of SPI with glycerin (50 g/100 g of dry SPI) was compression‐molded to obtain thermoplastic sheets. The weight‐average molecular weight (M_w) of the fractions, the structure, and the mechanical properties of the thermoplastic SPI sheets were investigated with light scattering, IR spectroscopy, wide X‐ray diffraction patterns, differential scanning calorimetry, ultraviolet spectroscopy, scanning electron microscopy, and tensile testing. After heating compression, the SPI sheets were transparent and exhibited a smooth and homogeneous structure. Moreover, the crystallinity degree of the thermoplastic SPI was obviously higher than that of the premix before compression because of the formation of intermolecular hydrogen bonding. The M_w's of the fractions were 1.17 × 10⁵ to 3.21 × 10⁵, and they increased with increasing pH value in fractionation. The mechanical properties and water resistance (R) of the SPI sheets increased with increasing M_w of the SPI fractions. The tensile strength and breaking elongation of the SPI sheets with an M_w value of 3.21 ×10⁵ were 5.7 MPa and 135%, respectively, and the R value was 0.54 after immersion in water for 15 days. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 3373–3380, 2001     

The reactive modification of polyethylene. I: The effect of low initiator concentrations on molecular properties

Commercial samples of high density, linear low density, and low density polyethylene were modified by injection of low concentrations of free radical initiator during extrusion. Molecular properties monitored included molecular weight distribution, degree of unsaturation, and branching. When the polyethylene teed to this reactive extrusion process had similar values of M_w, but varying polydispersity, degree of branching and degree of unsaturation, the magnitude of the change in molecular weight distribution was found to be in the following order: HDPE 1 > LDPE2 > LLDPE. In general, terminal vinyls enhanced molecular weight increase, and branching promoted degradation. However, for a second high density polyethylene sample with M_w = 154,000 (rather than the previous sample's M_w of 85,600), the change in molecular weight distribution was small and located at the lower molecular weight end. This work provided data for the kinetic model development detailed in Part II.     

Influence of polymer microstructure on the performance of post‐treated latex‐based pressure sensitive adhesives

Latex‐based butyl acrylate (BA)/acrylic acid (AA)/2‐hydroxyethyl methacrylate (HEMA) pressure sensitive adhesive (PSA) films with various microstructures were heated to improve their performance. The treated PSA films showed significantly better performance than original latex‐based PSA films with similar polymer microstructures. The effect of the heat treatment depended on the polymer microstructure of the untreated PSA films (or corresponding latices). Decreasing the amount of very small sol polymers (i.e., M_x < 2M_e) in gel‐free untreated PSA films, or both very small (i.e., M_x < 2M_e) and very large sol polymers (i.e., M_x > 20M_e) in gel‐containing untreated PSA films led to treated PSA films with significantly better performance. (Note: M_e is the molecular weight between two adjacent entanglement points in a polymer material.) In addition, simultaneously increasing the sol polymer molecular weight (M_w) as well as the size of the chain segments between two adjacent cross‐linking points (M_c) of the gel polymer in the original PSAs resulted in treated PSA films with better performance. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Rheological and mechanical properties of recycled polypropylene

In order to verify the possibility of manufacturing good quality articles by recycled polypropylene (PP), a study on the effect of many recycling operations on the rheological and mechanical properties of PP was conducted. The amount of degradation occurring during the reprocessing was estimated in the melt state by means of rheological measurements and the results obtained were correlated with the weight average molecular weight M_w and the molecular weight distribution MWD. Since the properties in the solid state are strictly dependent upon the molecular structure parameters and the morphology, mechanical properties were checked on films produced from virgin and recycled PP with a cast technology. Moreover, in order to estimate the effect of film composition and of the number of reprocessings on the final properties of the manufactured articles, blend films having different percentages of PP recycled several times and virgin PP were prepared.     

Effects of ionic strength and pH on the diffusion coefficients and conformation of chitosans molecule in solution

The effects of ionic strength and pH on the diffusion coefficients and gross conformation of chitosan molecules in solution were studied. Chitosan with 83% degree of deacetylation (DD) was prepared from red shrimp (Solemocera prominenitis) processing waste. Ten different molecular weight chitosans were prepared by ultrasonic degradation, and their molecular weights were determined by static light scattering. The weight-average molecular weight (M_w) were between 78 to 914 kilo dalton (KDa). Solution of different ionic strengths (I = 0.01, 0.10, and 0.20) but the same pH (2.18) and different pHs (2.37, 3.10, and 4.14) but the same ionic strength (I = 0.05) were prepared to measure their mutual diffusion coefficient (D_m). The diffusion coefficients for standard condition (D_20,w) were derived from D_m. Intrinsic viscosities ([η]) were determined by a capillary viscometer in different pH solutions. The Mark–Houwink exponents a and ε were obtained from plots of Log [η] and Log D_20,w versus Log M_w, respectively. The results show that diffusion coefficients increased with increasing ionic strength or with increasing pH or with decreasing M_w. Value of ε and a were between 0.503 to 0.571 and ranged from 0.543 to 0.632, respectively. The results indicates that chitosans conformation were in random coil in solutions in the ranges of ionic strength and pH studied. The values of a*, ε* and a**, ε**, Mark–Houwink exponents of smaller and higher than 223 KDa chitosans, respectively, were between 0.752 to 0.988 and 0.585 to 0.777 for smaller M_w chitosans and 0.406 to 0.428 and 0.430 to 0.518 for larger M_w chitosans, respectively. Molecular-weight-induced conformational transition occurred because smaller M_w chitosans was more extended than higher M_w chitosans. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 2041–2050, 1999     

The viscoelastic properties of rubber–resin blends. II. The effect of resin molecular weight

In blends of rubber and low molecular weight resins, the compatibility of the system controls the viscoelastic properties and ultimately the performance of the composition as a pressure sensitive adhesive. The effect of the resin molecular weight on compatibility was examined by studying rubber–resin blends prepared from resins which represent a range of molecular weights. Viscoelastic properties were measured using a mechanical spectrometer on 1:1 blends of rubber and a series of polystyrene resins and poly(vinylcyclohexane) resins. Based on plots of G′ and tan δ vs. temperature, blends of natural rubber and polystyrene resin show incompatibility at resin M_w of about 600 and above. Blends of natural rubber and poly(vinyl cyclohexane) are incompatible at resin M_w of about 1800, but are compatible at M_w of about 650. Blends of styrene–butadiene rubber and polystyrene resins are compatible at resin M_w of about 650 but appear to contain a low volume incompatible phase at M_w of about 900. Therefore, the compatibility of a rubber–resin blend depends upon the molecular weight of the resin. Even systems expected to be compatible will show evidence of incompatibility as the molecular weight of the resin is raised above some limiting value.     

Change in the molecular weight distribution of poly(ethylene oxide) caused by the complexation with poly(acrylic acid)

The complexation between poly(ethylene oxide) (PEO) and poly(acrylic acid) (PAA) was made by using double the molar quantity of either polymer component at pH 2 where the resulting complex completely precipitates. After the removal of the precipitate, PEO or PAA remaining in the supernatant was subjected to gel permeation chromatography to investigate the change in the molecular weight distribution (MWD) caused by the complexation. No remarkable difference is observed in the MWD curves for PEO[1] (M_w=1.37 × 10⁴) before and after the complexation with PAA[1] (M_w=1.10 × 10³) and PAA[2] (M_w=4.16 × 10⁵). However, the MWD curves of PEO[2] (M_w=1.26 × 10⁵) and PAA[2] become shortened and shift to the low molecular weight side after the complexation with PAA[1] or [2] and PEO[2], respectively. This tendency is enhanced by increasing the complexation temperature. From these results, it is indicated that the complexation between PEO and PAA deals with an equilibrium reaction, and the equilibrium constant is dependent on the chain length of both polymer components and also on the complexation temperature.     

The preparation of multiaxially oriented polyethylene morphologies with high mechanical properties in planar direactions

The development of multiaxially oriented films of low molecular weight (M_w ≈ 59,000) high density polyethylene with high mechanical properties in planer directions has been pursued by inducing fibrillar crystallization under curvilinear flow conditions in a contained geometry using an extrudomolding process and by simulating similar crystallization conditions in an optical plate–plate rheometer. The films, like the uniaxially drawn morphologies of the same low molecular weight high density polyethylene by solid-state extrusion, had a high modulus (12–20 GPa) and strength (0.25 GPa) along the residual flow lines but they exhibited also a modulus enhancement (5 GPa) in the transverse direction as a result of the orientation gradient of the molecular chains in the thickness directions.