Showing papers in "Journal of Applied Polymer Science in 1997"

Novel hydrophilic chitosan-polyethylene oxide nanoparticles as protein carriers

Abstract: Hydrophilic nanoparticulate carriers have important potential applications for the administration of therapeutic molecules. The recently developed hydrophobic-hydrophilic carriers require the use of organic solvents for their preparation and have a limited protein-loading capacity. To address these limitations a new approach for the preparation of nanoparticles made solely of hydrophilic polymers is presented. The preparation technique, based on an ionic gelation process, is extremely mild and involves the mixture of two aqueous phases at room temperature. One phase contains the polysaccharide chitosan (CS) and a diblock copolymer of ethylene oxide and propylene oxide (PEO-PPO) and, the other, contains the polyanion sodium tripolyphosphate (TPP). Size (200–1000 nm) and zeta potential (between +20 mV and +60 mV) of nanoparticles can be conveniently modulated by varying the ratio CS/PEO-PPO. Furthermore, using bovine serum albumin (BSA) as a model protein it was shown that these new nanoparticles have a great protein loading capacity (entrapment efficiency up to 80% of the protein) and provide a continuous release of the entrapped protein for up to 1 week. © 1997 John Wiley & Sons, Inc.

Synthesis of polypropylene oligomer—clay intercalation compounds

Abstract: The synthesis of polypropylene (PP) oligomer—clay intercalation compounds was studied by using three kinds of PP oligomers and organophylic clay. PP oligomers were two types of maleic-anhydride-modified PP oligomers containing different amount of maleic anhydride groups and one type of hydroxy modified PP oligomer. Organophylic clay was sodium-ion-exchanged montmorillonite with octadecylammonium ion (C18—Mt). PP oligomer was mixed with C18—Mt at 200°C. Maleic-anhydride-modified PP oligomer, which was of high acid value type, and hydroxy-modified PP oligomer were intercalated between silicate layers of clay; and PP oligomer—clay intercalation compounds were synthesized successfully. But maleic-anhydride-modified PP oligomer, which was of low acid value type, was not intercalated. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 1781–1785, 1997

Oil palm fibers: Morphology, chemical composition, surface modification, and mechanical properties

Abstract: Oil palm fiber is an important lignocellulosic raw material for the preparation of cost-effective and environment-friendly composite materials. The morphology and properties of these fibers have been analyzed. The properties of two important types of fibers, the oil palm empty fruit bunch fiber and the oil palm mesocarp fiber (fruit fiber) have been described. The surface topology of the fibers has been studied by scanning electron microscopy. Thermogravimetry and differential thermal analysis were used to determine the thermal stability of the fibers. Fiber surface modifications by alkali treatment, acetylation, and silane treatment were tried. The modified surfaces were characterized by infrared spectroscopy and scanning electron microscopy. The chemical constituents of the fibers were estimated according to ASTM standards. Mechanical performance of the fibers was also investigated. Microfibrillar angle of the fibers was theoretically predicted. The theoretical strength of the fibers was also calculated and compared with the experimental results. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 821–835, 1997

Citrate esters as plasticizers for poly(lactic acid)

Abstract: Citrate esters were used as plasticizers with poly(lactic acid) (PLA). Films were extruded using a single-screw extruder with plasticizer contents of 10, 20, and 30% by weight. All of the citrate esters investigated were found to be effective in reducing the glass transition temperature and improving the elongation at break. It was observed that the plasticizing efficiency was higher for the intermediate-molecular-weight plasticizers. Hydrolytic and enzymatic degradation tests were conducted on these films. It was found that the lower-molecular-weight citrates increased the enzymatic degradation rate of PLA and the higher-molecular-weight citrates decreased the degradation rate as compared with that of unplasticized PLA. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 1507–1513, 1997

Biodegradable polymer blends of poly(lactic acid) and poly(ethylene glycol)

Abstract: Poly(lactic acid) (PLA) and poly(ethylene glycol) (PEG) were melt-blended and extruded into films in the PLA/PEG ratios of 100/0, 90/10, 70/30, 50/50, and 30/70. It was concluded from the differential scanning calorimetry and dynamic mechanical analysis results that PLA/PEG blends range from miscible to partially miscible, depending on the concentration. Below 50% PEG content the PEG plasticized the PLA, yielding higher elongations and lower modulus values. Above 50% PEG content the blend morphology was driven by the increasing crystallinity of PEG, resulting in an increase in modulus and a corresponding decrease in elongation at break. The tensile strength was found to decrease in a linear fashion with increasing PEG content. Results obtained from enzymatic degradation show that the weight loss for all of the blends was significantly greater than that for the pure PLA. When the PEG content was 30% or lower, weight loss was found to be primarily due to enzymatic degradation of the PLA. Above 30% PEG content, the weight loss was found to be mainly due to the dissolution of PEG. During hydrolytic degradation, for PLA/PEG blends up to 30% PEG, weight loss occurs as a combination of degradation of PLA and dissolution of PEG. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 1495–1505, 1997

Mechanical behavior of sheets prepared from sugar beet cellulose microfibrils

Abstract: The mechanical behavior of films cast from sugar beet cellulose microfibrils was investigated through tensile tests. The obtaining of these microfibrils by chemical and mechanical treatments from the raw beet pulp is described. Depending on their purification level, individualization state, and moisture content, differences in tensile modulus are observed. It is found that pectins act as a binder between the cellulose microfibrils, which tends to increase the Young's modulus in dry atmosphere and to decrease it in moist conditions. The extraction of the cellulose microfibrils from the sugar beet cell wall and the obtainment of microfibril suspensions with partial individualization of the microfibrils by a mechanical treatment lead to the formation of a network of cellulose microfibrils within the film, which in turn increases the tensile modulus. Furthermore, the effect of the remaining pectins is compared with the effect of pectins previously removed and added to completely purified cellulosic microfibrils. As expected, once removed and so partly degraded, those pectins have nearly no influence on the mechanical properties. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 1185–1194, 1997

Mechanical properties of pineapple leaf fiber‐reinforced polyester composites

Abstract: Pineapple leaf fiber (PALF) which is rich in cellulose, relatively inexpen- sive, and abundantly available has the potential for polymer reinforcement. The present study investigated the tensile, flexural, and impact behavior of PALF-reinforced polyes- ter composites as a function of fiber loading, fiber length, and fiber surface modification. The tensile strength and Young's modulus of the composites were found to increase with fiber content in accordance with the rule of mixtures. The elongation at break of the composites exhibits an increase by the introduction of fiber. The mechanical proper- ties are optimum at a fiber length of 30 mm. The flexural stiffness and flexural strength of the composites with a 30% fiber weight fraction are 2.76 GPa and 80.2 MPa, respec- tively. The specific flexural stiffness of the composite is about 2.3 times greater than that of neat polyester resin. The work of fracture (impact strength) of the composite with 30% fiber content was found to be 24 kJ m 02 . Significant improvement in the tensile strength was observed for composites with silane A172-treated fibers. Scanning electron microscopic studies were carried out to understand the fiber-matrix adhesion, fiber breakage, and failure topography. The PALF polyester composites possess superior mechanical properties compared to other cellulose-based natural fiber composites. q 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 1739-1748, 1997

“Antiplasticization” in starch-glycerol films?

Abstract: Calorimetric, mechanical, and thermomechanical properties have been measured on starch films with various glycerol/water contents. For calorimetric measurements, a continuous decrease in Tg was observed as glycerol increases from 0 to 25%. Mechanical properties exhibit a minimum of elongation at break for glycerol content ∼ 12%. In slightly hydrated starch films not containing another plasticizer, a β relaxation is detected by DMTA around −68°C. This relaxation is modified by the presence of glycerol, the α relaxation of which appears in the same temperature range. Results are discussed comparing with the well-known antiplasticization effect in synthetic polymers such as PVC and PC. The combination of the plasticizer α mode and the polymer β mode is considered. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 63: 1047–1053, 1997

Structure and thermal/mechanical properties of poly (∈-caprolactone)-clay blend

Abstract: Montmorillonite was organically modified with distearyldimethylammonium chloride. This organically modified clay (OMON) and poly (ϵ-caprolactone) (PCL) were solvent-cast blended with chloroform, and the structure and properties of the resulting PCL-clay blends were investigated. From isothermal crystallization experiments, it was found that a small amount of OMON in the blend accelerated the crystallization of PCL, whereas a large amount of the organophilic clay delayed it. From small-and wide-angle X-ray scattering measurements, it was found that the silicate layers forming the clay could not be dispersed individually in the PCL blends. In other words, the clay seemed to exist as the tactoids consisting of some silicate layers. These tactoids formed a remarkable geometric structure; that is, their surface planes lay almost parallel to the blend film surface. Furthermore, the tactoids were stacked with insertion of PCL lamellae in the film-thickness direction. Preferred orientation of the PCL crystallites was induced by the presence of the clay. During the drawing process of the blends, fibrillation took place with formation of planelike voids developed on the plane parallel to the film surface. From dynamic viscoelastic measurements, it was shown that intercalation of PCL chains into the layered silicates did not take place in the blends prepared by the solvent-cast method used in this work. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 2211–2220, 1997

Agglomeration and electrical percolation behavior of carbon black dispersed in epoxy resin

Abstract: In conductive polymer compounds, the filler volume fraction at which a network of touching particles is formed is not a constant but depends on the manufacturing process. By applying three main features—particle-particle interaction, dynamics of agglomeration, and structure of agglomerates—which are well known in colloid science to filled polymers, the electrical percolation behavior can be understood. Thus, it is possible to explain the hitherto found low percolation thresholds of less than 0.5 vol% in carbon-black-filled resins and, hence, further reduce the threshold to 0.06 vol%. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 63: 1741–1746, 1997

Influence of glycerol and water content on the structure and properties of extruded starch plastic sheets during aging

Abstract: The properties of starch plastic sheets were investigated by stress—strain measurements in relation with starch crystallinity. Granular potato starch was plasticized with different amounts of glycerol and water by extrusion. The materials were amorphous directly after processing. During aging above the glass transition temperature at various humidities single helical (V and E-type) and double helical (B-type) crystallinity was formed. The rate of crystallization is a function of water and glycerol content. The amorphous rubbery materials were soft and weak with high elongations. During aging the materials became less flexible with higher elastic modulus and tensile stress. The changes are related to changes in water content and glass transition temperature and to changes in B-type crystallinity. The changes in stress—strain properties are explained by the formation of helical structures and crystals, which results in a reinforcement of the starch network by physical crosslinking. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 1411–1422, 1997

Isothermal crystallization and chain mobility of poly(L-lactide)

Abstract: Isothermal melt crystallization of poly(L-lactide) (PLLA) has been studied in the temperature range of 90 to 135°C. A maximum in crystallization kinetic was observed around 105°C. A transition from regime II to regime III is present around 115°C. The crystal morphology is a function of the degree of undercooling. At crystallization temperatures (Tc) below 105°C, further crystallization occurs upon heating; this behavior is not detected for Tc above 110°C. The analysis of the heat capacity increment at glass transition temperature (Tg) and of dielectric properties of PLLA indicates the presence of a fraction of the amorphous phase which does not relax at the Tg, and the amount of this so-called rigid amorphous phase is a function of Tc. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 911–919, 1997

Polypropylene–wood fiber composites: Effect of treatment and mixing conditions on mechanical properties

Abstract: Polypropylene/wood fiber composites were prepared at three different temperatures: 170°C, 180°C, and 190°C. The surface of wood fibers was modified through the use of silane coupling agents and/or coating with polypropylene or maleated polypropylene. The fiber coating was performed by propylene polymerization in the presence of wood fibers or by immersion in an o-dichlorobenzene polypropylene (or maleated polypropylene) solution. Tensile and three-point bending tests were performed in order to evaluate the adhesion between matrix and wood fibers. Evidence shows that 180°C is the best mixing temperature, while the use of vinyl-tris (2-methoxy ethoxy) silane with or without maleated polypropylene coating is the best surface treatment. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65:1227–1235, 1997

Studies on thermally stimulated shape memory effect of segmented polyurethanes

Abstract: The shape memory behavior of a series of polycaprolactone/diphenylmethane diisocyanate/butanediol (PCL/MDI/BDO) segmented polyurethanes of different composition was studied. The molecular weight of PCL diols was in the range of 1600-7000, and the hard segment content varied from 7.8 to 27% by weight. Film specimens for shape memory measurements were prepared by drawing at temperatures above the melting temperature of the soft segment crystals and subsequent quick cooling to room temperature under constrained conditions. The shape memory process was observed and recorded in a heating process. Parameters describing the recovery temperature, ability, and speed were used to study the influence of structure and processing conditions on the shape memory behavior of the sample. It was found that the high crystallinity of the soft segment regions at room temperature and the formation of stable hard segment domains acting as physical crosslinks in the temperature range above the melting temperature of the soft segment crystals are the two necessary conditions for a segmented copolymer with shape memory behavior. The response temperature of shape memory is dependent on the melting temperature of the soft segment crystals. The final recovery rate and the recovery speed are mainly related to the stability of the hard segment domains under stretching and are dependent on the hard segment content of the copolymers.

Flexible polyurethane foam. I. Thermal decomposition of a polyether‐based, water‐blown commercial type of flexible polyurethane foam

Abstract: This study of the pyrolysis of a flexible polyurethane foam showed that the composition of the products depends on the conditions of the pyrolysis. If the volatiles are removed rapidly from the system, they will contain tolylene diisocyanate (TDI). However, under confined conditions, the TDI will be replaced by diamino toluene (DAT). These results can be explained by assuming two decomposition routes to be operative; one leading to the regeneration of the two source materials, TDI and the polyol; the other to DAT and a double-bond-terminated polyether (the polyol with its terminal hydroxy groups replaced by double bonds). The TDI route is the faster, however: if the volatile TDI is confined to the pyrolysis zone, an equilibrium will be established between the urethane group and the TDI plus polyol. Such conditions will favor the slower, though irreversible, route leading to the formation of DAT. On pyrolysis, the urea groups in the foam dissociates into TDI and DAT. These will recombine in the vapor phase to form an aerosol of polyurea. It is proposed that this aerosol is the “yellow smoke” reported in the literature.12,27 © 1997 John Wiley & Sons, Inc.

Diffuse reflectance Fourier transform infrared spectra of wood fibers treated with maleated polypropylenes

Abstract: The esterification reaction between wood fibers and maleated polypropylenes was investigated. The reaction was conducted in a reactor in the presence of xylene used as a solvent and sodium hypophosphite as catalyst. The reaction between wood fibers and pure maleic anhydride was also investigated. The appearance of an infrared absorption band near 1730 cm−1 indicated that maleated polypropylene chemically reacted by esterification with bleached Kraft cellulose. However, no direct evidence of an esterification reaction was obtained between thermomechanical pulp and maleated polypropylene. The Fourier transform infrared (FTIR) studies showed also that both bleached Kraft cellulose and thermomechanical pulp reacted with maleic anhydride with the formation of ester links. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 1163–1173, 1997

Poly(vinyl alcohol)‐clay and poly(ethylene oxide)‐clay blends prepared using water as solvent

Abstract: Montmorillonite (MON) was solvent-cast blended with poly(vinyl alcohol) (PVA) and poly(ethylene oxide) (PEO) using water as cosolvent. The structure and properties of the blend films have been investigated. From small- and wide-angle X-ray scattering measurements of the blends, the silicate layers of MON are found to be well dispersed individually in the PVA-MON blends, while the silicate layers in PEO-MON blends are found to exist in the form of a large clay tactoid. Furthermore, for both blends, it is found that the silicate layers are parallel to the film surface of the blends, and that preferred orientation of polymer crystallites is induced by the presence of MON. The effects of the MON content on the thermal behavior of the PVA- and PEO-MON blends have been studied with a differential scanning calorimeter. Furthermore, the effects of geometry of the silicate layers on dynamic behavior of the blends have been studied. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 573–581, 1997

Phosphorus-containing epoxy for flame retardant. III: Using phosphorylated diamines as curing agents

Abstract: Two phosphorus-containing diamine compounds, bis(4-aminophenoxy)-phenyl phosphine oxide and bis(3-aminophenyl)phenyl phosphine oxide, were synthesized for use as curing agents of epoxy resins. Phosphorylated epoxy resins were obtained by curing Epon 828 and Eponex 1510 with these two diamine agents. For raising the phosphorus contents of the resulting epoxy resins, the phosphorus-containing epoxy, bis(glycidyloxy)phenyl phosphine oxide (BGPPO), was also used. These two diamine agents showed similar reactivity toward epoxies. Their reactivities were higher than DDS and lower than DDM. High char yields in TGA evaluation were found for all the phosphorylated epoxy resins, implying their high flame retardancy. The excellent flame-retardant properties of these phosphorylated epoxy resins were also demonstrated by the high limiting oxygen index (LOI) values of 33 to 51. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 63: 895–901, 1997

Rheological properties of carboxymethyl cellulose

Abstract: This work is a complete and comprehensive study of the rheological properties of carboxymethyl cellulose (CMC) solutions. The study was carried out using the computer controlled RheoStress RS100 system of Haake. CMC concentration in the test solutions ranged by weight from 1 to 5%. This range was sufficiently wide to reveal the nearly Newtonian behavior at the lower end of concentrations, and the definitely pseudoplastic, thixotropic, and viscoelastic behaviors of CMC solutions at the higher end of concentrations. The scope of the study included measurements of steady-state parameters, transient shear stress response, and yield stress. In addition, the thixotropic, creep recovery, and dynamic responses of solutions with high concentrations were measured. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 289–301, 1997

Effect of size, surface charge, and hydrophobicity on the translocation of polystyrene microspheres through gastrointestinal mucin

Abstract: Microspheres (MS) have been proposed for use as oral vaccine delivery vehicles (VDV); however, due to poor and variable absorption their clinical utility is limited. The effects of size, ζ-potential, and surface hydrophobicity on the translocation (PT) permeabilities of polystyrene (PS) MS with varying surface functional groups (amidine, carboxyl, carboxylate-modified [CML], and sulfate) were determined through gastrointestinal (GI) mucin. PT were determined, under steady-state conditions, using a modified Ussing-type diffusion chamber and a mucin packet developed for use with the Transwell-Snapwell system. PT followed the Stokes-Einstein relationship, demonstrating the limited ability of larger MS (>0.5 μm) to diffuse through the mucin layer. PT also varied according to the surface characteristics. Even though the ζ-potential did not correlate with the transport of MS through mucin, surface ionization appears to be important in MS translocation. The PS-amidine MS were significantly less hydrophobic and had a higher PT than that of the other MS, suggesting that hydrophobicity is also a significant factor in MS transport through mucin. While these results suggest that mucin may be a significant barrier to the oral absorption of vaccines and VDVs in vivo, the rate-limiting barrier for the absorption of MS will be the intestinal mucosa. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 63: 1481–1492, 1997

Bamboo fiber‐reinforced polypropylene composites: Crystallization and interfacial morphology

Abstract: Bamboo fiber-reinforced polypropylene (PP) composites were prepared. PP and two maleated polypropylenes (s-MAPP and m-MAPP) were used as matrices. Crystallization and interfacial morphology were studied by using differential scanning calorimetry (DSC), wide angle X-ray diffraction (WAXD), and optical microscopy. It has been shown that the addition of bamboo fiber to any of the three polymers causes an increase in the overall crystallization rate. A considerable amount of β-form crystallinity was produced in the PP, s-MAPP, and m-MAPP by mixing with bamboo fiber; and all the bamboo fiber-filled samples contain both the α- and the β-forms. The relative amount of the β-form in the samples was calculated from WAXD data by the K value. There is no β-form observed in the pure PP, s-MAPP, and m-MAPP. Bamboo fiber acted as both a reinforcement and a β-nucleator. The nucleation density of both s-MAPP and m-MAPP at the fiber surface is remarkably higher than that of PP because an improved interfacial adhesion is reached in the case of s-MAPP and m-MAPP as matrices. The transcrystalline growth of s-MAPP and m-MAPP on the bamboo fiber surface was observed under optical microscope with crossed polars. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 1267–1273, 1997

The effect of average soft segment length on morphology and properties of a series of polyurethane elastomers. II. SAXS‐DSC annealing study

Abstract: A series of eight thermoplastic polyurethane elastomers were synthesized from 4,4′-methylene diphenyl diisocyanate (MDI) and 1,4-butanediol (BDO) chain extender, with poly(hexamethylene oxide) (PHMO) macrodiol soft segments. The PHMO molecular weights employed ranged from 433 g/mol to 1180 g/mol. All materials contained 60% (w/w) of the macrodiol. The materials were characterized by differential scanning calorimetry (DSC) following up to nine different thermal treatments. In addition, three of the materials were selected for characterization by small-angle x-ray scattering (SAXS) following similar thermal treatments. The DSC experiments showed the existence of five hard segment melting regions (labelled T1-T5), which were postulated to result from the disordering or melting of sequences containing one to five MDI-derived units, respectively. Evidence for urethane linkage dissociation and reassociation during annealing at temperatures above 150°C is presented. This process aids in the formation of higher melting structures. Annealing temperatures of 80–100°C provided the maximum SAXS scattering intensity values. Materials containing longer soft segments (and, therefore, longer hard segments) were observed to develop and sustain higher melting hard domain structures and also develop maximum average interdomain spacing values at higher annealing temperatures. Another additional series of three PHMO-based polyurethanes having narrower hard segment length distributions, was synthesized and characterized by DSC in the as-synthesized and annealed states. The resulting DSC endotherms provided further evidence to suggest that the T1-T5 endotherms were possibly due to melting of various hard segment length populations.

Comparison of the fracture and failure behavior of injection‐molded α‐ and β‐polypropylene in high‐speed three‐point bending tests

Abstract: The fracture and failure mode of α- and β-isotactic polypropylene (α-iPP and β-iPP, respectively) were studied in high speed (1 m/s) three-point bending tests on notched bars cut from injection-molded dumbbell specimens and compared. The fracture response of the notched Charpy-type specimens at room temperature (RT) and −40°C, respectively, was described by terms of the linear elastic fracture mechanics (LEFM), namely fracture toughness (Kc) and fracture energy (Gc). Kc values of both iPP modifications were similar, while Gc values of the β-iPP were approximately twofold of the reference α-iPP irrespective of the test temperature. It was demonstrated that β-iPP failed in a ductile and brittle-microductile manner at RT and −40°C, respectively. By contrast, brittle fracture dominated in α-iPP at both testing temperatures. Based on the fracture surface appearance, it was supposed that β-to-α (βα) transformation occurred in β-iPP. The superior fracture energy of β-iPP to α-iPP was attributed to a combined effect of the following terms: morphology, mechanical damping, and phase transformation. Results indicate that their relative contribution is a function of the test temperature. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 2057–2066, 1997

Effect of degree of deacetylation of chitin on the properties of chitin crystallites

Abstract: In the present article, chitin from crab shell was systematically deacetylated using a NaOH treatment with control of the reaction time. The degree of deacetylation, monitored using solid-state NMR, revealed that the reaction was pseudo-first order. Based on this, swollen and NaOH-saturated particles are proposed as the reaction system. The weight loss of the partially saponified and neutralized samples after HCl hydrolysis increased linearly with the degree of deacetylation. The crystallinity of the samples was found to increase after acid hydrolysis. According to conductimetric titration, the surface charge density of the crystallites, after acid hydrolysis, was found to increase with base treatment time. The effect of surface charge on the formation of a chiral nematic phase, due to the rodlike nature of the crystallites, was explored. These results show that because the contribution of charged particles to the ionic strength was significant the double layer compression was affected, especially since the surface charge density was close to the Manning limit. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65:373–380, 1997

Conductive Blends of Thermally Dodecylbenzene Sulfonic Acid-Doped Polyaniline with Thermoplastic Polymers

Abstract: In the present study, a conductive polyaniline-dodecyl benzene sulfonic acid (PANI-DBSA) complex, prepared by a thermal doping process, and its blends with thermoplastic polymers, prepared by melt processing, were investigated. PANI- DBSA characterization included conductivity measurements, morphology, crystallogra- phy, and thermal behavior. The blends' investigation focused on the morphology and the interaction between the components and on the resulting electrical conductivity. The level of interaction between the PANI and the matrix polymer determines the blend morphology and, thus, its electrical conductivity. Similar solubility parameters of the two polymeric components are necessary for a high level of PANI dispersion within the matrix polymer and, thus, enable the formation of conducting paths at low PANI content. The morphology of these blends is described by a two-structure hier- archy: (a) a primary structure, composed of small dispersed polyaniline particles, and (b) a short-range fine fibrillar structure, interconnecting the dispersed particles. q 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 243-253, 1997

Polyetherimide-modified epoxy networks: Influence of cure conditions on morphology and mechanical properties

Abstract: The morphologies and mechanical properties of thermoplastic-modified epoxy networks generated through the reaction-induced phase separation procedure were studied as a function of isothermal cure conditions. The selected model system was diglycidyl ether of bisphenol A cured with 4,4′-methylenebis [3-chloro,2,6-diethylaniline] in the presence of a nonfunctionalized polyetherimide. Appropriate precuring and postcuring schedules were selected. The precure temperature had a strong effect on final morphologies because it affected the viscosity of the system at the cloud point and the extent of the separation process. The morphologies generated are discussed in connection with phase separation mechanisms. The ratio of the height of the loss peaks corresponding to each phase was an appropriate parameter to qualitatively predict the shape of morphology and to determine if the system was phase-inverted or not. The fracture toughness, KIc was significantly improved only when bicontinuous or inverted structures were generated, resulting from the plastic drawing of the thermoplastic-rich phase. Before phase inversion, KIc was hardly higher than that of the neat matrix due to poor interfacial adhesion. Nevertheless, the thermoplastic-rich particles constitute obstacles to the propagation of the crack and contribute to the toughening of the material, measured through impact resistance measurements. The observation of fracture surfaces revealed the occurrence of microcracking and crack-pinning. Strain recovery experiments showed that particle-induced shear yielding of the matrix was present as well. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65: 2433–2445, 1997

Effect of Air-Gap Distance on the Morphology and Thermal Properties of Polyethersulfone Hollow Fibers

Abstract: By using 30/70 polyethersulfone/NMP (N-methyl-2-pyrrolidone) solutions as an example, we have determined the role of air-gap distance on nascent fiber mor- phology, performance, and thermal properties An increase in air-gap distance results in a hollow fiber with a less layer of fingerlike voids and a significant lower permeance For the first time we have reported that the Tg of a dry-jet wet-spun fiber prepared from one-polymer/one-solvent systems is lower than that of a wet-spun fiber, and Tg decreases with an increase in air-gap distance These interesting phenomena arise from the fact that different precipitation paths take place during the wet-spinning and dry-jet wet-spinning processes Wet-spun fibers experience vigorous and almost instantaneous coagulations; it results in hollow fiber skins with a long-range random, unoriented chain entanglement, but loose structure Dry-jet wet-spun fibers first go through a moisture-induced phase separation process and then a wet-phase inversion process; it results in external fiber skins with a short-range random, compact, and slightly oriented or stretched structure As a result, the outskin of wet-spun fibers have a greater free volume and a higher first Tg than that of the dry-jet wet-spun ones Both SEM (scanning electronic microscope) photomicrographs and DSC (differential scanning calorimeter) analyses support our conclusion q 1997 John Wiley & Sons, Inc J Appl Polym Sci 66: 1067-1077, 1997

Properties of Fatty-Acid Esters of Starch and Their Blends with LDPE

Abstract: In the present study, starch octanoates OCST1.8 and OCST2.7 with degrees of substitution (d.s.) of 1.8 and 2.7, respectively, and dodecanoate DODST2.7 (d.s. A 2.7), were prepared by esterification of native starch with fatty acid chlorides. Our analyses, including elemental analysis, FTIR, contact angle, DSC, and TGA measure- ments confirmed the esterification reaction of starch and the degree of substitution. The ester group was found to act like an internal plasticizer, with an increase in the number and the size of fatty acyl chains grafted onto starch. These starch esters were mixed with low density polyethylene (LDPE) at various proportions in a Haake Rheo- mixer. Water and moisture absorption, thermal and mechanical properties, and biodeg- radation were investigated as a function of blend composition. The DODST2.7/LDPE blends showed, in general, better thermal stability and higher elongation, but lower tensile strength and water absorption, than did corresponding OCST/LDPE blends. The addition of starch esters to LDPE led to a very slow rate of biodegradation of these blends. q 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65: 705-721, 1997

Effect of moisture absorption on the thermal properties of Bombyx mori silk fibroin films

Abstract: Films of regenerated Bombyx mori silk are strongly affected by absorbed moisture, a phenomenon studied here by differential scanning calorimetry (DSC). Exposure of previously dried films to environments of controlled relative humidity produces test samples of well-defined equilibrium moisture content. Ultimate moisture uptake is as high as 20–23% (by weight) at 75% relative humidity. The glass transition temperature, Tg, drops by 40°C at moisture uptakes as low as 2%, and Tg depressions as large as 140°C are observed at higher relative humidity. The moisture-induced decrease of Tg is completely reversible, as a film remoistened and then redried possesses an unchanged Tg. Trends in Tg with water uptake correspond reasonably well to predictions of a classical thermodynamic theory, indicating that the plasticization effect of moisture on the combined silk-water system can be satisfactorily explained from macroscopic properties of the constituents without any reference to specific interactions. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 63: 401–410, 1997