Showing papers in "Journal of Applied Polymer Science in 1996"

Properties and modification methods for vegetable fibers for natural fiber composites

Abstract: SYNOPSIS Studies on structure and properties of natural vegetable fibers (NVF) show that composites made of NVF combine good mechanical properties with a low specific mass. The high level of moisture absorption by the fiber, its poor wettability, as well as the insufficient adhesion between untreated fibers and the polymer matrix lead to debonding with age. To build composites with high mechanical properties, therefore, a surface modification of the fibers is necessary. The existing physical and chemical NVF modification methods-e.g., plasma treatment or graft copolymerization-which are used for the development of NVF-polymer composite properties is discussed. It is shown that modified cellulose fiber-polymer interaction mechanisms are complex and specific to every definite system. By using an coupling agent, like silanes or stearin acid, the Young's modulus and the tensile strength increases, dependent on the resin, until 50%. Simultaneously, the moisture absorption of the composites decreases for about 60%. With other surface modifications, similar results are obtained. 0 1996 John Wiley & Sons, Inc

Effect of molecular weight and crystallinity on poly(lactic acid) mechanical properties

Abstract: Several samples of poly(lactic acid) with different molecular weights and tacticity have been prepared, and some PLLA injection moulded specimens have been annealed to promote their crystallization. From the characterization data, poly(L-lactide) showed more interesting mechanical properties than poly(D, L-lactide), and its behavior significantly improves with crystallization. In fact, annealed specimens possess higher values of tensional and flexural modulus of elasticity, Izod impact strength, and heat resistance. The plateau region of flexural strength as a function of molecular weights appears around Mv = 35,000 for PDLLA and amorphous PLLA and at higher molecular weight, around Mv = 55,000, for crystalline PLLA. The study of temperature effect shows that at 56°C only crystalline PLLA still exhibits useful mechanical properties. © 1996 John Wiley & Sons, Inc.

Preparation and Characterization of PMMA-Clay Hybrid Composite by Emulsion Polymerization

Abstract: Nanocomposites are prepared by a simple technique of emulsion polymerization using MMA monomer and Na+-montmorillonite. The products are purified by hot toluene extraction and characterized by FT-IR, X-ray diffraction, TGA, DSC, and tensile testing. The structural investigation confirms that the products are intercalated with PMMA chain molecules oriented parallel to the direction of lamellar layers whose separation is consequently more enlarged than in the polymer-free clay. DSC traces also corroborate the confinement of the polymer in the inorganic layer by exhibiting no observable transition in the thermogram. Both the thermal stability and tensile properties of the products appear to be substantially enhanced. The ion-dipole bonding is believed to be the driving force for the introduction and fixation of the organic polymer to the interfaces of montmorillonite. © 1996 John Wiley & Sons, Inc.

Structure and properties of shape-memory polyurethane block copolymers

Abstract: Segmented polyurethanes containing soft segments with lower molecular weight exhibit shape-memorizing properties. Structure and properties of shape-memorizing polyurethanes (S-PUs) were studied. S-PUs are characterized by a rather high glass transition temperature: Tg of S-PUs is usually in the range of 10–50°C. A Pplot of 1/Tm against–In XA is approximately linear, indicating that the hard segments are randomly distributed along the molecular chain. S-PUs with a hard segment of 67–80 mole % form negative spheruiites; they give a faint scattering maximum in a small-angle X-ray diffraction pattern. On the other hand, S-PUs with a hard segment of 50 mole % form fine birefringent elements, giving diffuse scattering in its SAXD pattern. A cyclic test of an S-PUs above Tg indicates that the residual strain increases and the recovery strain decreases with increasing cycle and maximum strain. It has been suggested by dynamic mechanical investigation that the shape-memorizing property of the S-PUs may be ascribed to the molecular motion of the amorphous soft segments. © 1996 John Wiley & Sons, Inc.

Crystallization kinetics of poly(L‐lactide‐co‐meso‐lactide)

Abstract: The crystallization kinetics of poly(L-lactide-co-meso-lactide) were determined over a range of 0% to 9% mesolactide. The kinetics were fit to the nonlinear Avrami equation and then to the Hoffman–Lauritzen equation modified for optical copolymers. The theory was found to fit the data well. The crystallization half-time was found to increase about 40% for every 1 wt % meso-lactide in the polymerization mixture. The change in crystallization rate is driven mainly by the reduction in melting point for the copolymers. The copolymer crystallization kinetics were also determined in the presence of talc, a nucleating agent for polylactide. The theory again fit the data well, using the same growth parameters and accounting for the talc only through the nucleation density term. © 1996 John Wiley & Sons, Inc.

Tensile properties of short sisal fiber reinforced polystyrene composites

Abstract: The tensile properties of polystyrene reinforced with short sisal fiber and benzoylated sisal fiber were studied. The influence of fiber length, fiber content, fiber orientation, and ben-zoylation of the fiber on the tensile properties of the composite were evaluated. The ben-zoylation of the fiber improves the adhesion of the fiber to the polystyrene matrix. the benzoylated fiber was analyzed by IR spectroscopy. Experimental results indicate a better compatibility between benzoylated fiber and polystyrene. the benzoylation of the sisal fiber was found to enhance the tensile properties of the resulting composite. The tensile properties of unidirectionally aligned composites show a gradual increase with fiber content and a leveling off beyond 20% fiber loading. The properties were found to be almost independent of fiber length although the ultimate tensile strength shows marginal improvement at 10 mm fiber length. The thermal properties of the composites were analyzed by differential scanning calorimetry. Scanning electron microscopy was used to investigate the fiber surface, fiber pullout, and fiber–matrix interface. Theoretical models have been used to fit the experimental mechanical data. © 1996 John Wiley & Sons, Inc.

Injection molding of polypropylene reinforced with short jute fibers

Abstract: Composites with polypropylene (PP) and jute fiber were prepared by injection molding technique. Maleic anhydride-grafted polypropylene was added as coupling agent to improve the adhesion between jute fiber and PP. A high fiber attrition was noted during injection molding, which had negative effects on the mechanical properties of the composites. The coupling agent improved the tensile and bending strengths, however the elastic and bending moduli were found not to be influenced by the coupling agent. The role of the average fiber length in strengthening of the composites was interpreted with help of the critical fiber length. Fracture surfaces of the composites, and the fiber orientations, were investigated by scanning electron microscopy and light microscopy, respectively. © 1996 John Wiley & Sons, Inc.

Thermal and mechanical properties of aluminum powder-filled high-density polyethylene composites

Abstract: Thermal conductivity and mechanical properties such as tensile strength, elongation at break, and modulus of elasticity of aluminum powder-filled high-density polyethylene composites are investigated experimentally in the range of filler content 0–33% by volume for thermal conductivity and 0–50% by volume for mechanical properties. Experimental results from thermal conductivity measurements show a region of low particle content, 0–12% by volume, where the particles are distributed homogeneously in the polymer matrix and are not interacting with each other; in this region most of the thermal conductivity models for two-phase systems are applicable. At higher particle content, the filler tends to form ag-glomerates and conductive chains resulting in a rapid increase in thermal conductivity. The model developed by Agari and Uno estimates the thermal conductivity in this region. Tensile strength and elongation at break decreased with increasing aluminum particles content, which is attributed to the introduction of discontinuities in the structure. Modulus of elasticity increased up to around 12% volume content of aluminum particles. Einstein's equation, which assumes perfect adhesion between the filler particles and the matrix, explains the experimental results in this region quite well. For particle content higher than 30%, a decrease in the modulus of elasticity is observed which may be attributed to the formation of cavities around filler particles during stretching in tensile tests. © 1996 John Wiley & Sons, Inc.

Biodegradable lactone copolymers. I: Characterization and mechanical behavior of ε-caprolactone and lactide copolymers

Abstract: Copolymers of e-caprolactone and L-lactide (e-CL/L-LA) and e-caprolactone and DL-lactide (e-CL/DL-LA) were synthesized with compositions 80/20, 60/40, and 40/60 (wt % in feed). The polymerization temperature was 140°C and Sn(II)octoate was used as a catalyst. The effect of the comonomer ratio on the thermal and mechanical properties of the copolymers was investigated by size-exclusion chromatography (SEC), differential scanning calorimetry (DSC), nuclear magnetic resonance (NMR) spectrometry, and tensile testing. The copolymers differed widely in their physical characteristics, ranging from weak elastomers to tougher thermoplastics according to the ratio of e-CL and LA in the copolymerization. Poly(L-lactide) (PLLA), poly(DL-lactide) (PDLLA), and poly(e-caprolactone) (PCL) homopolymers were studied as references. The tensile modulus and tensile strength were much higher for PLLA, PDLLA, and PCL homopolymers than for the copolymers. The maximum strain was very low for PLLA and PDLLA, whereas the copolymers and PCL exhibited large elongation. © 1996 John Wiley & Sons, Inc.

Chitosan/calcium—alginate beads for oral delivery of insulin

Abstract: A mild chitosan/calcium alginate microencapsulation process, as applied to encapsulation of biological macromolecules such as albumin and insulin, was investigated. The microcapsules were derived by adding dropwise a protein-containing sodium alginate mixture into a chitosan–CaCl2 system. The beads containing a high concentration of entrapped bovine serum albumin (BSA) as more than 70% of the initial concentration were achieved via varying chitosan coat. It was observed that approximately 70% of the content is being released into Tris-HCl buffer, pH 7.4 within 24 h and no significant release of BSA was observed during treatment with 0.1M HCl pH 1.2 for 4 h. But the acid-treated beads had released almost all the entrapped protein into Tris-HCl pH 7.4 media within 24 h. Instead of BSA, the insulin preload was found to be very low in the chitosan/calcium alginate system; the release characteristics were similar to that of BSA. From scanning electron microscopic studies, it appears that the chitosan modifies the alginate microspheres and subsequently the protein loading. The results indicate the possibility of modifying the formulation in order to obtain the desired controlled release of bioactive peptides (insulin), for a convenient gastrointestinal tract delivery system. © 1996 John Wiley & Sons, Inc.

Crystallinity and morphology of segmented polyurethanes with different soft-segment length

Abstract: A series of polycaprolactone/4,4′-diphenylmethane diisocyanate/1,4-butanediol (PCL/MDI/BDO) segmented polyurethanes of different compositions was synthesized by solution polymerization. The molecular weight of PCL diols used was in the range of 1600–7000. The crystallinity and morphology of these polymers were studied by using DSC, dynamic mechanical analysis, WAXD, and polarizing microscopy methods. It was found that the crystallinity of PCL prepolymers was depressed in segmented polyurethanes. A lower limit of PCL molecular weight was found, below which the PCL segments were not able to crystallize at the usual processing conditions. This limit of molecular weight is in the range of 2000–3000 and exhibits a slight increase with increasing hard-segment content of polyurethanes. The glass transition temperature related to the PCL segment regions in polyurethane specimens deviated from that of pure amorphous PCL prepolymer to a higher temperature. The deviation resulted from the crystallization of PCL segments and also the influence of hard segments. The formation of hard-segment domains becomes very difficult for polyurethanes having low hard-segment content and short hard-segment length. There is a lower limit of hard-segment content and segment length. Only above that limit do the polyurethanes have enough hard-segment domains acting as physical crosslinks at temperatures above the melting point of the PCL crystals. The structural characteristics of segmented polyurethanes which may exhibit a shape memory effect are also discussed. © 1996 John Wiley & Sons, Inc.

Effects of β-α transformation on the static and dynamic tensile behavior of isotactic polypropylene

Abstract: It was demonstrated that the mechanical stress-induced βα-transformation in isotactic polypropylene (iPP) is associated with considerable toughness enhancement. This toughness improvement depends on the test conditions (loading frequency). The toughness of β-iPP was superior to the α-iPP by 13% under static (characterized by a load frequency of ca. 5 × 10−4 Hz) and 70% under dynamic (tensile impact with a loading frequency in the range of ca. 3 × 102…103 Hz) conditions, respectively. By applying the essential work of fracture (EWF) concept to single-edge notched tensile (SEN-T) specimens it was shown that for the toughness upgrading observed, energy dissipation in the enlarged plastic zone is responsible. The occurrence of the βα-transformation was evidenced by differential scanning calorimetry (DSC). Based on DSC measurements it was found that the degree of βα-trans-formation depends on the local strain. At high strain values the βα-conversion is complete (at elogation at break in uniaxial static tensile test), while this transformation is only partial at lower strains (at tensile impact). In addition, in the plastic (or deformation) zone the βα-conversion changed locally, and can be used for mapping of this region. © 1996 John Wiley & Sons, Inc.

Blends of aliphatic polyesters. I. Physical properties and morphologies of solution-cast blends from poly(DL-lactide) and poly(ε-caprolactone)

Abstract: Effects of the mixing ratio of poly(DL-lactide) (PDLLA) and poly (e-caprolactone) (PCL) on the thermal and mechanical properties and morphologies of the solution-cast blends were investigated by differential scanning calorimetry (DSC), polarizing microscopy, tensile tests, and dynamic mechanical analysis. The presence of amorphous PDLLA did not disturb crystallization of PCL over the PDLLA content [XPDLLA = PDLLA/(PCL + PDLLA)] from 0.1 to 0.9 and allowed PCL to form spherulites over XPDLLA ranging from 0.1 to 0.6. The spherulite radius was larger for the blends than for the nonblended PCL. Phase separation occurred for the blends with XPDLLA between 0.1 and 0.9 Tm of PCL remained unchanged in the XPDLLA range up to 0.6 but decreased at XPDLLA above 0.6, whereas the crystallinity of PCL was constant around 60%, irrespective of XPDLLA. The tensile strength (σB, the yield stress (σY), the Young's modulus(E), and the storage modulus (G′) of the blends increased monotonously with XPDLLA if σB at XPDLLA = 0 and 0.6 and σY at XPDLLA = 0.6 were excluded. Elongation-at-break (eB) of PDLLA increased dramatically, while eB of PCL decreased remarkably when a small amount of the other component was added. Equations and parameters predicting σY, E, and G′ of the PCL-PDLLA blends were proposed as a function of XPDLLA. © 1996 John Wiley & Sons, Inc.

Synthesis and characterization of polyfunctional naphthoxazines and related polymers

Abstract: SYNOPSIS In pursuing the new polymers that could provide high mechanical properties and good thermal stabilities, a series of naphthoxazines are synthesized from different hydroxynaphthalenes with aniline and formaldehyde. The molecular structures are confirmed by NMR spectroscopy. After being polymerized in an autoclave, the naphthoxazine derived from 1,5dihydroxynaphthalene is successfully cured to form the void-free resin. The density and tensile properties of these polynaphthoxazines are measured. Dynamic mechanical tests are performed to determine the TR, crosslink density, and the activation enthalpy of the glass transition process for the polynaphthoxazines postcured in air at different temperatures. The effect of postcure temperature on the Tgs of the polynaphthzoxazines is investigated and discussed in terms of crosslink density. The polynaphthoxazine shows a T, higher than the cure temperature. Fourier transform IR spectroscopy is applied for the molecular characterization of the curing systems. Thermal properties of these polynaphthzoxazines are studied in terms of the weight loss after isothermal aging in static air, the decomposition temperature from thermogravimetric analysis, and the change of dynamic storage moduli at high temperatures. 0 1996 John Wiley & Sons, Inc.

Mechanical properties of silver‐powder‐filled polypropylene composites

Abstract: Mechanical properties, such as tensile and flexural properties, as well as impact behavior of silver-powder-filled isotactic polypropylene composites were investigated in the composite composition range of 0–5.6 vol% of Ag. Tensile modulus, strength, and elongation at break decreased with incorporation of silver and an increase in silver concentration. Analysis of tensile strength data indicated the introduction of stress concentration and discontinuity in the structure upon addition of Ag particles. Izod impact strength decreased sharply on addition of 0.43 vol % of Ag particles, beyond which the value decreased marginally. Both flexural modulus and strength increased with filler content due to an increase in rigidity. Surface treatment of filler marginally improved mechanical properties. © 1996 John Wiley & Sons, Inc.

Superabsorbent polymeric materials. I. Swelling behaviors of crosslinked poly(sodium acrylate‐co‐hydroxyethyl methacrylate) in aqueous salt solution

Abstract: A series of crosslinked poly(sodium acrylate-co-hydroxyethyl methacrylate) based on sodium acrylate (SA), 2-hydroxyethyl methacrylate (HEMA), and N,N′-methylene-bis-acrylamide (NMBA) are prepared by inverse suspension polymerization. The resultant crosslinking polymers are xerogellants. This work investigates not only the absorbency or swelling behavior for these xerogellants composed of different ratios of HEMA/SA in water, but also the effects of various salts and pH values on the swelling properties. Experimental results indicate that the absorbency in deionized water decreases with an increase in the HEMA in copolymeric gel, which is related to the degree of expansion of the network and the strength of the hydrophilic group. The absorbency in the chloride salt solutions decreases with an increase in the salt concentration (swelling is 50 times for the IA group chloride salt solutions, but is less than 5 times for the IIA group salt solution), owing to the osmosis of water and ions between the polymeric gel and the external solution. A decrease in the extent of swelling occurs for divalent and trivalent chloride salt solutions. For the salt solutions of the same ionic strength, the swelling amount has the following tendency: LiCl(aq) = NaCl(aq) = KCl(aq), CaCl2(aq) Ca2+ > Zn2+ > Cu2+. These orders are related to the complexing ability between metallic cations and the carboxylate group in the polymeric chains. Finally, the adsorption of ferric ion by these gels is also investigated. © 1996 John Wiley & Sons, Inc.

Formation and Structure of Polyacrylamide Gels

Abstract: SYNOPSIS Acrylamide and N,N-methylenebis(acry1amide) (AAm-Bis) copolymerization has been investigated in water at a monomer concentration of 1.8 w/v %. Conversion of monomer and pendant vinyl groups was measured as a function of the reaction time up to the onset of macrogelation. Experimental results indicate that 80% of pendant vinyl groups are consumed by cyclization reactions. When the monomer concentration was kept constant at 1.8%, the critical conversion at the gel point shows a minimum at 7.5 mol % Bis. The equilibrium degree of swelling of the polyacrylamide (PAAm) gels is independent of their crosslinker content. Calculation results show that the average reactivity of pendant vinyl groups for intermolecular links decreases as the Bis concentration increases. All these results suggest formation of PAAm microgels prior to the onset of macrogelation. As the reaction proceeds, microgels are connected to a macrogel through their peripheral pendant vinyls and radical ends, whereas those in their interior remain intact. The microgels seem to act as the junction points of the final inhomogeneous networks. 0 1996 John Wiley & Sons, Inc.

A Kinetic-Model for Sulfur Accelerated Vulcanization of a Natural-Rubber Compound

Abstract: Vulcanization kinetics for a natural rubber compound were studied by a kinetic approach using the cure meter and DSC methods. A simplified but realistic model reaction scheme was used to simulate induction, curing, and overcure periods continuously. Physically significant parameters of the model were extracted from isothermal experimental data using a cure meter. The calculation demonstrated a good correspondence with isothermal cure meter data over the temperature range studied. The length of induction time, variation of maximum modulus with temperature, and the reversion phenomena observed from cure curves can be predicted. DSC data were found to be incompatible with the cure meter test, because the complex vulcanization reaction system is multiexothermal and it is difficult to isolate the heat due to crosslinking. Hence, the cure meter technique is suggested for the study of crosslink formation. The kinetic approach provides a way to incorporate vulcanization kinetics into simulation of reactive processing operations. © 1996 John Wiley & Sons, Inc.

The effect of average soft segment length on morphology and properties of a series of polyurethane elastomers. I. Characterization of the series

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 soft segment molecular weights employed ranged from 433 g/mol to 1180 g/mol. All materials contained 60% (w/w) of the soft segment macrodiol. Differential scanning calorimetry (DSC), dynamic mechanical thermal analysis (DMTA), wide angle x-ray diffraction (WAXD), and small angle x-ray scattering (SAXS) techniques were employed to characterize morphology. Tensile and Shore hardness tests were also performed. Materials were tested in the annealed state. It was found that an increase in segment length was accompanied by an increase in the degree of microphase separation, average interdomain spacing, hard domain order, hardness, stiffness, and opacity. DSC experiments showed the existence of several hard segment melting regions that were postulated to result from the disordering or melting of various hard segment length populations. For the system and composition ratio employed, it was found that optimum tensile properties (UTS and breaking strain) were achieved when a PHMO molecular weight of between 650 and 850 was utilized.

Low earth orbit resistant siloxane copolymers

Abstract: Two classes of siloxane copolymers were evaluated for their resistance to the low earth orbit (LEO) environment. Poly(imide–siloxane) (PISX) copolymers were used as the resin for PISX–carbon fiber composites. These composites were exposed to the LEO environment, for 50 h, as part of the “Effect of Oxygen Interaction with Materials” (EOIM-III) experiment aboard the space shuttle STS-46. XPS analysis showed primarily silicon oxides on the LEO-exposed surfaces and evidence of a thermally accelerated oxidation. The results of simulated LEO exposure of the PISX composites show that they are one to two orders of magnitude more resistant than are homopolyimide-based composites. Furthermore, we found, surprisingly, that these materials erode slower when far-UV radiation is combined with the atomic oxygen. XPS analysis of PISX exposed only to far-UV allowed a partial mechanism to be proposed for the effect of far-UV radiation on the PISX copolymers. Polyhedral oligosilsequioxane (POSS)–siloxane copolymers were evaluated in a simulated LEO environment and results indicate that the POSS–siloxane copolymers are even more resistant to the simulated LEO environment than are the PISX copolymers; POSS–siloxanes actually gained weight during the exposure and healed the microcracks present. © 1996 John Wiley Sons, Inc.

Phosphorus-containing epoxy for flame retardant. I. Synthesis, thermal, and flame-retardant properties

Abstract: A new phosphorus-containing oxirane, bis-(3-glycidyloxy)phenylphosphine oxide (BGPPO), was synthesized. Further curing BGPPO with diamine curing agents, dicyanodiamide (DICY), 4,4′-diaminodiphenylmethane (DDM), and 4,4′-diaminodiphenylsulfone (DDS), respectively, resulted in several phosphorylated epoxy resins. Compared with Epon 828, Eponex 1015, and DER 732, BGPPO showed relatively high reactivity toward diamine agents via DSC studies. Furthermore, the reactivity of the three curing agents toward BGPPO were found to be in the order of DDM > DICY > DDS. Thermal stability and the weight loss behavior of the cured polymers were studied by TGA. The phosphorylated resins showed lower weight loss temperatures and higher char yields than did the Epon 828-based resins. The high char yields as well as high limited oxygen index (LOI) values of the BGPPO-based resins confirmed the effectiveness of phosphorus-containing epoxy resins as flame retardants. © 1996 John Wiley & Sons, Inc.

Emulsion and miniemulsion copolymerization of acrylic monomers in the presence of alkyd resin

Abstract: Emulsion and miniemulsion copolymerizations were carried out with acrylic monomers (methyl methacrylate, butyl acrylate, and acrylic acid) in the presence of an alkyd resin. Poly(methyl methacrylate) was used as a hydrophobe or cosurfactant in the miniemulsion reactions. The results demonstrate that miniemulsion polymerization is the preferred process, probably because of mass transport limitations of the alkyd in the conventional emulsion polymerization reactions. The monomer emulsions prepared for the miniemulsion reactions were much more stable and the polymerizations were free of coagulum. Reaction rates, particle size characteristics, grafting efficiencies, and some film properties were measured. © 1996 John Wiley & Sons, Inc.

Effect of soft-segment CH2/O ratio on morphology and properties of a series of polyurethane elastomers

Abstract: A series of six thermoplastic polyurethane elastomers were synthesized from a 4,4′-methylene diphenyl diisocyanate (MDI) and 1,4-butanediol (BDO) chain extender, with poly(ethyleneoxide) (PEO), poly(tetramethylene oxide) (PTMO), poly(hexamethylene oxide) (PHMO), poly(octamethylene oxide) (POMO), poly(decamethylene oxide) (PDMO), and poly(1,6-hexyl carbonate)diol (PCDO) macrodiol soft segments. The soft-segment molecular weights employed were similar (approximately 1000 g/mol) and each polyurethane contained 55% (w/w) of the soft-segment macrodiol. Differential scanning calorimetry (DSC), dynamic mechanical thermal analysis (DMTA), wide-angle X-ray diffraction (WAXD), and Fourier transform infrared spectroscopy (FTIR) techniques were employed to characterize the morphology. Tensile and Shore hardness tests were also performed. Materials were tested in the as-molded, solvent-cast, and annealed states. It was found that the polyurethanes produced from macrodiols with the highest CH2/O ratio displayed greater hard-domain crystallinity, a higher degree of phase separation, and the greatest hardness, stiffness, and opacity. POMO- and PDMO-based polymers displayed evidence of paracrystallinity in the soft domains. The PCDO-based material displayed a higher degree of phase mixing compared to the polyether-based materials. Annealing increased hard-domain crystallinity in all the polyether-based materials. The solvent-cast POMO- and PDMO-based materials had poor mechanical properties and were difficult to cast. The materials containing macrodiols with the lowest CH2/O ratio were more readily solvent-cost and produced strong, useful films. Morphologies of the solvent-cast materials differed greatly from those of the molded materials. © 1996 John Wiley & Sons, Inc.

Crystallization behavior of polypropylene filled with surface‐modified talc

Abstract: Talc-filled polypropylene (PP) composites were prepared by extrusion in a wide composition range (0–40 wt %). To improve the affinity relation between talc and the PP matrix, we modified the talc surface with silane coupling agents. Differential scanning calorimetry investigations on test samples, prepared by injection moulding, revealed that the talc content and its surface modification had a pronounced effect on the crystallization behavior of the filled PP composites. The experimental results indicate that a talc concentration of 2 wt % strongly affects the nonisothermal crystallization process of the PP, especially when talc is silane treated Isothermal crystallization experiments on samples with minimum amounts of talc (2 wt %) revealed an improved nucleation activity with silane-treated talc. © 1996 John Wiley & Sons, Inc.

Interaction of supercritical carbon dioxide with polymers. I: Crystalline polymers

Abstract: Supercritical fluid (SCF) technology involving carbon dioxide is recently receiving wide attention due to its vast potential application in various fields such as cleaning, extraction, synthesis, etc., in addition to its environmental benefits. To fully exploit the use of SCFs in new technologies, it is important to understand how SCFs interact with materials. To this end, we have undertaken a systematic study involving a wide pressure and temperature range to investigate the interaction of supercritical carbon dioxide (SC CO2) with nine different crystalline polymers, namely, substituted and unsubstituted polyethylene (four varieties), polypropylene, nylon 66, poly(ethylene terephthalate), poly(oxymethylene), and poly(vinylidine fluoride). Critical factors such as changes in appearance and weight, temperature, pressure and time of the supercritical fluid treatment, and dimension of samples have been observed. The influence of SC CO2 on the thermal properties of treated polymers has been investigated through TGA analysis. Further, changes in the mechanical properties such as yield strength, ultimate elongation, and modulus of elasticity of the investigated crystalline polymers were also observed. A discussion has been included to show the possible implications of the observed changes in realizing various applications. © 1996 John Wiley & Sons, Inc.

Interaction of supercritical carbon dioxide with polymers. II. Amorphous polymers

Abstract: In continuation of our goal to implement supercritical fluid (SCF) technology for various applications such as precision cleaning, foaming, and impregnation of materials, a systematic study has been performed involving amorphous polymers. Eleven different polymers of amorphous nature have been subjected to supercritical carbon dioxide (SC CO2) treatment under a wide pressure and temperature range (1000–3000 psi and 25–70°C, respectively). The influence and impact of such treatment on the appearance, weight change, and thermal and mechanical properties were followed systematically. In addition, the effect of treatment conditions and dimension of the samples on weight changes were also monitored. It has been found that amorphous polymers can absorb carbon dioxide to a greater extent than crystalline polymers and, in turn, the phenomenon of plasticization was also very high. In addition to morphology, the polarity of the polymer is also crucial in determining the solubility in carbon dioxide. Comparison was also made with the behavior of crystalline polymers. © 1996 John Wiley & Sons, Inc.

Chemical modification of polypropylene with peroxide/pentaerythritol triacrylate by reactive extrusion

Abstract: To explore the possibility of producing branched polypropylene (PP) by a reactive extrusion (REX) process, isotactic PP was reacted with a polyfunctional monomer, pentaerythritol triacrylate (PETA), in the presence of 2,5-dimethyl-2,5(t-butylperoxy) hexane peroxide (Lupersol 101). Experiments were carried out in an intermeshing, corotating twin-screw extruder at 200°C using three concentrations of peroxide (200, 600, and 1000 ppm) and four concentrations of PETA (0.64, 1.8, 2.8, and 5.0%, by weight). Shear viscosity and MFI of the whole polymers was found to increase with PETA concentration and decrease with increasing the peroxide concentration at a given PETA concentration. The macrogel amount in the materials produced was determined in refluxing xylene using Soxhlet extraction and at PETA concentrations higher than 1.8wt % the macrogel content increased with increasing peroxide concentration. No macrogel was detected at low PETA concentrations (<0.64%) at all three peroxide levels, suggesting that low concentrations of PETA and peroxide should be used in order to minimize the formation of macrogels. The xylene soluble portions (sols) of the modified materials were characterized by FTIR and DSC. Generally, the relative intensities A1740/A841 in the FTIR spectra increased with increasing PETA incorporated into PP. Two melting peaks (Tm1 and Tm2) were observed in the DSC traces of some of the sols, and the crystallization temperatures (Tc) were higher than those of the virgin and degraded polypropylenes. The DSC behavior of the sols suggests that the modified PPs contain branched and/or lightly crosslinked chain structures. © 1996 John Wiley & Sons, Inc.

Texture profile analysis of bioadhesive polymeric semisolids: Mechanical characterization and investigation of interactions between formulation components

Abstract: This study reports the use of texture profile analysis (TPA) to mechanically characterize polymeric, pharmaceutical semisolids containing at least one bioadhesive polymer and to determine interactions between formulation components. The hardness, adhesiveness, force per unit time required for compression (compressibility), and elasticity of polymeric, pharmaceutical semisolids containing polycarbophil (1 or 5% w/w), polyvinylpyrrolidone (3 or 5% w/w), and hydroxyethylcellulose (3, 5, or 10% w/w) in phosphate buffer (pH 6.8) were determined using a texture analyzer in the TPA mode (compression depth 15 mm, compression rate 8 mm s−1, 15 s delay period). Increasing concentrations of polycarbophil, polyvinylpyrrolidone, and hydroxyethylcellulose significantly increased product hardness, adhesiveness, and compressibility but decreased product elasticity. Statistically, interactions between polymeric formulation components were observed within the experimental design and were probably due to relative differences in the physical states of polyvinylpyrrolidone and polycarbophil in the formulations, i.e., dispersed/dissolved and unswollen/swollen, respectively. Increased product hardness and compressibility were possibly due to the effects of hydroxyethylcellulose, polyvinylpyrrolidone, and polycarbophil on the viscosity of the formulations. Increased adhesiveness was related to the concentration and, more importantly, to the physical state of polycarbophil. Decreased product elasticity was due to the increased semisolid nature of the product. TPA is a rapid, straightforward analytical technique that may be applied to the mechanical characterization of polymeric, pharmaceutical semisolids. It provides a convenient means to rapidly identify physicochemical interactions between formulation components. © 1996 John Wiley & Sons, Inc.

PP–elastomer–filler hybrids. I. Processing, microstructure, and mechanical properties

Abstract: Three-component systems with a polypropylene (PP) matrix consisting of polar elastomer (ethylene–propylene rubber and styrene–ethylene–butylene–styrene grafted with maleic anhydride) or of polar PP (PP grafted with maleic anhydride) and filler were investigated. Three microstructures of PP–elastomer–filler hybrids were obtained by processing control and elastomer or PP modification with the maleic anhydride: fillers and rubber particles were separated in the PP matrix, rubber particles with filler core were distributed in the PP matrix, and mixed microstructures of the first and second. A study of mechanical properties showed that the elastic modulus increased in the first microstructure and impact strength increased in the second microstructure. Mechanisms for the relationships between microstructure, processing, and mechanical properties are discussed. © 1996 John Wiley & Sons, Inc.

Chemical Modification of Epoxy-Resins by Dialkyl(or Aryl) Phosphates - Evaluation of Fire Behavior and Thermal-Stability

Abstract: The improvement of flame-retardation of thermosetted epoxy–amine resins was attempted by chemically incorporating phosphorus-containing reagents. By reacting 4,4′-diglycidylether of bisphenol A (DGEBA) with dialkyl (or aryl) phosphate, it was possible to chemically modify the epoxy resin and then cure it in the presence of 4,4′-diaminodiphenylsulfone (DDS) to obtain epoxy-amine resin with good flame-retardant and thermal stability behaviors. The quantitative aspect of the addition of dialkyl (or aryl) phosphate onto glycidyle oxiranes was evaluated by elemental analysis of the modified epoxy-amine resins. Flammability and thermal behaviors of modified DGEBA/DDS resins depend on the nature of phosphate groups (the best flame-retardation was observed on resins bearing phenyl phosphate groups) and their concentration in the material. In relation to DGEBA/DDS samples containing additives of the same structure [trialkyl(or aryl) phosphate], cured resins incorporating chemically bonded phosphate groups show a better flame-retardation. On the contrary to the nonomodified DGEBA/DDS [with or without trialkyl (or aryl) phosphate as additive], combustion of modified DGEBA/DDS resins is accompanied by formation of intumescent char. Chemical modification of DGEBA by dialkyl (or aryl) phosphates can be carried out in situ during the curing of epoxy resins without change in the fire behavior. © 1996 John Wiley & Sons, Inc.