Mechanical properties and blend compatibility of natural rubber –chlorosulfonated polyethylene blends

Natural rubber (NR) was blended with chlorosulfonated polyethylene (CSM) with various formulation and blend ratios (NR/CSM: 80/20 –20/80, wt/wt). Rubber blends were prepared by using a two‐roll mill and vulcanized in a compression mold to obtain the 2 mm‐thick sheets. Tensile properties, tear resistance, thermal aging resistance, ozone resistance, and oil resistance were determined according to ASTM. Compatible NR/CSM blends are derived from certain blends containing 20–30% CSM without adding any compatibilizing agent. Tensile and tear strength of NR‐rich blends for certain formulations show positive deviation from the rule of mixture. Thermal aging resistance depends on formulation and blend ratio, while ozone and oil resistance of the blends increase with CSM content. Homogenizing agents used were Stuktol®60NS and Epoxyprene®25. Stuktol®60NS tends to decrease the mechanical properties of the blends and shows no significant effect on blend morphology. Addition of 5–10 phr of epoxidized natural rubber (ENR, Epoxyprene® 25) increases tensile strength, thermal aging resistance, and ozone resistance of the blends. It is found that ENR acts as a compatibilizer of the NR/CSM blends by decreasing both CSM particle size diameter and α transition temperature of CSM. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 127–140, 2006     

Synthesis and characterization of bioactive molecules grafted on poly(?-caprolactone) by “click” chemistry

A facile and efficient strategy to graft bioactive molecules (nicotinic acid, p-aminobenzoic acid, and phthaloyltryptophan) onto poly(?-caprolactone) (P(?CL)) was achieved by copper-catalyzed Huisgen’s 1,3-dipolar cycloaddition known as click reaction. P(αCl?CL), with 10, 20, and 30% of α-chloro-?-caprolactone (αCl?CL) units were copolymerized by ring opening polymerization using ?CL and αCl?CL as starting materials in the presence of 1,4-butanediol and Sn(Oct)₂. Subsequently, the chloride pendent was converted to azide followed by cycloaddition with terminal alkyne derivatives of the aforementioned bioactive molecules. The complete addition was accomplished at all ratios. The characteristic molecular features of these copolymers were evaluated by FTIR, NMR, and GPC. Thermal analysis data indicated that the grafted compounds led to polymorphic alteration and different pattern of thermal degradation depending on the molecular structure and the size of the grafted compounds. They are the basis for further development of grafted copolymer as drug delivery carriers.     

Synthesis and thermal properties of natural rubber grafted with poly(2-hydroxyethyl acrylate)

A novel modified natural rubber with grafted poly(2-hydroxyethyl acrylate) (NR-g-PHEA) was synthesized by emulsion polymerization in latex stage. Cumene hydroperoxide and tetraethylene pentamine were used as redox initiators (1:1 M ratio). The influences of reaction temperature, reaction time, initiator concentration and monomer concentration on percent grafting and grafting efficiency were investigated. Transmission electron microscopy was used to observe the NR-g-PHEA particles, which exhibited core-shell morphology. Chemical structure of purified NR-g-PHEA was confirmed by Fourier transform infrared spectroscopy and proton nuclear magnetic resonance spectroscopy. The thermal properties were examined by thermogravimetric analysis and by differential scanning calorimetry. The modified NR had improved thermal stability, and the NR-g-PHEA also presented slightly higher glass transition temperature than virgin NR.     

The effect of epoxide content on compatibility of poly(lactic acid)/epoxidized natural rubber blends

The objective of this work was to determine the effect of the epoxide content in epoxidized natural rubber (ENR) on the miscibility and compatibility with poly(lactic acid) (PLA) in prepared PLA/ENR blends. PLA was blended with 10 wt% of ENRs (epoxidized at 10, 15, 20, and 25 mol%). The presented study showed that the in situ graft copolymer, PLA-g-ENR, was formed during melt blending in the blends containing 10 and 15 mol% ENR. This work is the initial study showing the presence of PLA-g-ENR in the blends by ¹H-NMR and ¹³C-NMR. PLA-g-ENR acted as a compatibilizer, producing a partially miscible blend, indicated by an inward shift of the α-transition temperatures of PLA and ENR in the blends. PLA-g-ENR also greatly reduced the particle size of ENR and increased the impact strength, tensile strength, and elongation at break of the blends. The epoxide content of ENR changed deformation mechanisms of the blends.     

The effect of cetyl palmitate crystallinity on physical properties of gamma-oryzanol encapsulated in solid lipid nanoparticles

This present study was aimed at investigating the effect of the crystallinity of cetyl palmitate based solid lipid nanoparticles (SLNs) on the physical properties of γ-oryzanol-loaded SLNs. SLNs consisting of varying ratios of cetyl palmitate and γ-oryzanol were prepared. Their hydrodynamic diameters were in the range 210-280?nm and the zeta potentials were in the range -27 to -35?mV. The size of SLNs increased as the amount of cetyl palmitate decreased whereas no significant change of zeta potentials was found. Atomic force microscopy pictures indicated the presence of disc-like particles. The crystallinity of SLNs, determined by differential scanning calorimetry and powder x-ray diffraction, was directly dependent on the ratio of cetyl palmitate to γ-oryzanol and decreased with decreasing cetyl palmitate content in the lipid matrix. Varying this ratio in the lipid mix resulted in a shift in the melting temperature and enthalpy, although the SLN structure remained unchanged as an orthorhombic lamellar lattice. This has been attributed to a potential inhibition by γ-oryzanol during lipid crystal growth as well as a less ordered structure of the SLNs. The results revealed that the crystallinity of the SLNs was mainly dependent on the solid lipid, and that the crystallinity has an important impact on the physical characteristics of active-loaded SLNs.     

Design of an IV Formulation of an Unstable Prodrug Candidate for Prostate Cancer Treatment: Solution Chemistry of N-(glutaryl-hyp-ala-ser-cyclohexylglycyl-gln-ser-leu)-doxorubicin

ABSTRACT

The chemical degradation of N-(glutaryl-hyp-ala-ser-cyclohexylglycyl-gln-ser-leu)-doxorubicin (henceforth referred to as doxorubicin peptide conjugate 1) was studied in buffered aqueous solution. The pH-rate profile of degradation shows that the doxorubicin conjugate is most stable between pH 5 and 6. The dependence of log k_obsd on pH in acidic medium is characteristic of specific acid-catalysis of the sugar hemiaminal of 1 (as in the case of doxorubicin). Isolation of degradates and structural determination shows that the degradation at lower pH values yields the water-insoluble aglycone doxorubicinone, supporting the mechanism of acid-catalyzed loss of the amino sugar. At pH higher than 5, a more complicated degradation pattern is observed, including the loss of the amino sugar and the aromatization of the saturated ring to give 7,8-dehydro-9,10-desacetyldoxorubicinone as one of the major products. Around the pH of maximum stability in solution, the rate of degradation of 1 is significantly greater than that for doxorubicin, which rules out the formulation of a room temperature solution product with a sufficiently long shelflife for market use. Design of a stable lyophilized formulation for sterile reconstitution based on the physicochemical properties of 1 is described.     

Toughness enhancement of poly(lactic acid) by melt blending with natural rubber

Rubber toughened poly(lactic acid) (PLA) was prepared by blending with natural rubber (NR)‐based polymers. The blends contained 10 wt % of rubber and melt blended with a twin screw extruder. Enhancement of impact strength of PLA was primarily concernced. This study was focused on the effect of rubber polarity, rubber viscosity and molecular weight on mechanical properties of the blends. Three types of rubbers were used: NR, epoxidized natural rubber (ENR25 and ENR50), and natural rubber grafted with poly(methyl methacrylate) (NR‐g‐PMMA). Effect of viscosity and molecular weight of NR, rubber mastication with a two‐roll mill was investigated. It was found that all blends showed higher impact strength than PLA and NR became the best toughening agent. Viscosity and molecular weight of NR decreased with increasing number of mastication. Impact strength of PLA/NR blends increased after applying NR mastication due to appropriate particle size. DMTA and DSC characterization were determined as well. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Effect of different curing systems on heat shrinkability and mechanical properties of ethylene vinyl acetate/epoxidized natural rubber blends

Ethylene vinyl acetate (EVA)/epoxidized natural rubber (ENR) blends containing 10 and 30 wt % ENR were prepared by using an internal mixer. Five different types of curing systems were employed: dicumyl peroxide (DCP), sulfur (S), phenolic resin (Ph), DCP + S, and DCP + Ph. DCP could crosslink with both EVA and ENR while S and Ph were curing agents for ENR. The DCP system provided the lowest tensile properties and tear strength because of low crosslinking in ENR phase. Addition of sulfur or phenolic resin increased the mechanical properties due to a better vulcanization of the rubber phase. The mechanical properties of the blends decreased with increasing ENR content. The rubber particle size in the blends containing 30% ENR played a more important role in the mechanical properties than the blends containing 10% ENR. ENR particle size did not affect heat shrinkability of EVA and a well vulcanized rubber phase was not required for high heat shrinkage. Furthermore, heat shrinkage of the blends slightly changed as the ENR content increased for all curing systems. With regard to the mechanical properties and heat shrinkability, the most appropriate curing system was DCP + Ph and in the case the 10 wt % ENR content produced a more favorable blend. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Synthesis and characterization of elastomeric,biobased, nonisocyanate polyurethane from natural rubber

Linear and crosslinked polyhydroxyurethanes (PHUs) based on natural rubber (NR) were synthesized by a polyaddition reaction without a solvent or catalyst to exploit the reactivity of diamines or triamines with dicyclic carbonate groups. Oligo‐isoprenes were obtained from the controlled oxidative degradation of NR and successive modifications of the chain ends. The syntheses of linear PHU were carried out with two approaches. The first one consisted of a reaction between amino telechelic oligo‐isoprenes and aromatic or aliphatic dicyclic carbonates. The second approach proceeded through a reaction between oligo‐isoprenes bearing cyclic carbonate chain ends and difunctional or trifunctional amines. The evolution of these reactions was studied by Fourier transform infrared spectrometry. The influence of the carbonate‐to‐amine molar ratio, the chain length of the oligo‐isoprenes, and the reaction temperatures were investigated. The thermal properties of the PHUs were studied by differential scanning calorimetry and thermogravimetric analysis. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45427.     

Comparison of microwave and thermal cure of epoxy–anhydride resins: Mechanical properties and dynamic characteristics

The objective of this work was to compare the mechanical properties of epoxy resins cured by thermal heating and microwave heating. Epoxy–anhydride (100:80) resins were cured in a domestic microwave oven and in a thermal oven. The hardening agents included methyl tetrahydrophthalic anhydride and methyl hexahydrophthalic anhydride. Three types of accelerators were employed. Thermal curing was performed at 150°C for 20 and 14 min for resins containing 1 and 4% accelerator, respectively. Microwave curing was carried out at a low power (207 or 276 W) for 10, 14, and 20 min. All cured resins were investigated with respect to their tensile properties, notched Izod impact resistance, and flexural properties (three‐point bending) according to ASTM standards. The tan δ and activation energy values were investigated with dynamic mechanical thermal analysis, and the extent of conversion was determined with differential scanning calorimetry. The differences in the mechanical properties of the thermally cured and microwave‐cured samples depended on the resin formulation and properties. Equivalent or better mechanical properties were obtained by microwave curing, in comparison with those obtained by thermal curing. Microwave curing also provided a shorter cure time and an equivalent degree of conversion. The glass‐transition temperatures (tan δ) of the thermally and microwave‐cured resins were comparable, and their activation energies were in the range of 327–521 kJ/mol. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 1442–1461, 2005