Abstract Bioabsorbable composites were fabricated from poly(D, L‐lactide‐urethane) matrix reinforced with poly(glycolic acid) (DEXON) surgical mesh. The crosslinked polyurethane matrix was formed from the reaction of ethy1–2, 6‐diisocyanatohexanoate and poly (D, L‐lactide) triol, initiated from glycerol; the ultimate degradation products of this matrix, L‐lysine, lactic acid, glycerol, and CO 2 , are all nontoxic, naturally occurring metabolites. The composites were fabricated by two processing methods, with the final composite structures displaying very different physical properties. Composites fabricated by vacuum bag molding displayed tensile strength and modulus of 66 MPa and 468 MPa, respectively, with total elongation of 39%. Composites fabricated by the same method, but whose final cure included 24 h at 5000 psi, displayed tensile strength and modulus of 86 MPa and 3.4 Gpa, respectively, with total elongation of 18%, suggesting a more fully developed matrix/fiber interphase and a reduction in microvoids, which lead to lower force failures. As poly(D, L‐lactide) prepolymer molecular weights decreased, tensile strengths and glass transition temperatures of the polyurethane networks increased. These trends were attributed to increased hydrogen bonding with an increased crosslink density. The composites were sensitive to cyclic loading, regardless of the processing technique, suggesting an inefficient transfer of energy from the matrix into the load‐bearing fibers. This weakness was confirmed by SEM microscopy, which revelaed a gap at the fiber/matridx interface of an unfatigued composite sample, poly(D, L‐lactide‐urethane) matrix composites were found to be unique since they can be custom shaped when heated above the glass transition of the matrix. DSC revelaed the glass transitions for the matrices of around 60°C. The composites were easily shaped above this temperature, yet remained rigid at biological temperature.
Abstract The kinetics of plasticizer absorption by suspension polymerized polyvinylchloride (PVC) have been investigated. The volume swelling ratios of individual PVC particles, immersed in excess plasticizer, were recorded over a period of time using an optical microscope equipped with a high speed camera, Absorption of din‐decylphthalate was studied in the range 70 < T < 100°C. The study shows that the uptake of plasticizer proceeds in three steps: (1) a slow initial absorption into glassy PVC, which is a thermally activated rate process, wherein the polymer is being progressively solvated and evolving toward the rubbery state, (2) the considerable faster diffusion of plasticizer into a rubbery, dynamic polymer matrix, and (3) the asymptotic approach to the equilibrium swelling capacity. Temperature dependency of rate of absorption in the slow initial step was fitted to an Arrhenius expression, and an activation energy for plasticizer uptake was calculated.
ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTInvestigation of the diffusion of di-n-hexyl phthalate in rubbery poly(vinyl chloride) using electrical impedance spectroscopyDeyan Wang, R. F. Storey, and Kenneth A. MauritzCite this: Macromolecules 1992, 25, 11, 2869–2874Publication Date (Print):May 1, 1992Publication History Published online1 May 2002Published inissue 1 May 1992https://pubs.acs.org/doi/10.1021/ma00037a013https://doi.org/10.1021/ma00037a013research-articleACS PublicationsRequest reuse permissionsArticle Views74Altmetric-Citations3LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access optionsGet e-Alertsclose Get e-Alerts
Abstract An initial series of energy calculations is aimed at predicting the epitactic behavior of S 2 N 2 as deposited from the vapor phase upon NaCl‐type alkali halide substrates and preferred orientation of molecular chains in the (SN) x polymerized phase. Although the preferred orientation of a single S 2 N 2 molecule is identical for NaCl and NaF, the energetics of dimer formation on the surface greatly favor use of the latter substrate as a heterogeneous nucleation catalyst. Enhancement of dimer formation on NaF is due to a near match between S 2 N 2 –S 2 N 2 equilibrium distance and substrate unit‐cell spacing. Furthermore, the (SN) x chain‐orientation tendency also appears to be a function of alkali halide type. On NaCl, the chain axis lies along the 〈110〉 surface direction above cationic rows, the plane of interatomic bonds being perpendicular to the surface. For NaF the axial direction is 〈100〉 with alignment between rows of alternating charge, with the molecular plane in this case parallel to the substrate surface. From the calculations it appears that primary Coulombic forces are not a significant factor in dictating the epitactic properties of monomer or polymer.
Abstract Sol‐gel reactions of tetraethylorthosilicate were conducted within the nanophase‐separated morphology of Nafion® films to yield Nafion®/silicate nanocomposites. The chemical aging of silicate phase molecular structure when the nanocomposites were exposed to (1) ambient air, (2) applied heat, (3) liquid water, (4) methanol reflux, and (5) heated sulfuric acid was explored by means of 29 Si solid state NMR spectroscopy. In particular, the characteristic chemical shifts and relative Intensities of peaks that identify Q n = (HO) 4‐n Si(OSi) n molecular subunits in silicate structures were determined for samples exposed to these aging conditions. Shifts in the Q peak distribution reflected the evolution of degree of Si atom coordination about SiO 4 units. The coordination states are always Q 4 and Q 3 although a small Q 2 population is occasionally present. Thus, a significant degree of silicate phase coordination can develop despite constraints posed by the Nafion® medium. Percent Q 4 increases in all cases but then reaches a maximum after which it decreases, the greatest de‐polymerization being for samples aged in water. The greatest increase in Q 4 relative to the un‐aged control occurred for samples heated at 100°C. Exposure to ambient air produced changes in Q 4 that were small, but not insignificant. While the initial increase in Si atom substitution around SiO 4 units can be rationalized in terms of gradual condensation reactions between residual SiOH groups, accompanied by the liberation of water molecules and their removal from the site of the reaction, the eventual decrease in coordination is not currently understood.
