Iranian polymer journal
Volume:21 Issue: 10, 2012

Sulfonated polymer/silica hybrid nanoparticles were prepared by free radical polymerization of 2-acrylamido-2-methyl-1-propane sulfonic acid (PAMPS-g-SN) and styrene sulfonic acid sodium salt (PSSA-g-SN), initiated on the surfaces of aminopropyl-functionalized silica nanoparticles (ASN). Ce(IV) ammonium nitrate/nitric acid and sodium dodecyl sulfate were used as redox initiator and stabilizer, respectively. ASN Nanoparticles were synthesized by a covalently attached 3-aminopropyltriethoxysilane onto the surface of silica nanoparticles. Sulfonated monomers (AMPS or SSA) were then grafted onto the ASN nanoparticles, ultrasonically dispersed in water, using redox initiator system at 40 °C. ASN, PAMPS-g-SN and PSSA-g-SN nanoparticles were characterized by Fourier transform infrared (FTIR), thermogravimetry, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) analyses. FTIR and TGA results indicated that both AMPS and SSA monomers were successfully grafted onto the silica nanoparticles. The grafted amounts of sulfonated polymers onto the silica nanoparticles were estimated from TGA thermograms to be 46 and 22 % for PAMPS and PSSA, respectively. From SEM and TEM micrographs, the average-diameters of the polymer-grafted silica nanoparticles were measured to be <50 nm with a (semi)spherical morphology, in which several silica nanoparticles were able to form a core with PAMPS or PSSA existing around the silica nanoparticles.

Polyethylene terephthalate (PET) bottles are widely used for packaging mineral water or soft drinks. Migration of toxic residual phthalate esters from PET could potentially change the quality of the bottled contents. The main purpose of this study is to control the migration of five different phthalate esters from PET bottles into the water they contained. To achieve this goal, three different types of nanoclay particles were added to PET to slow down the migration of the toxic phthalate esters. The concentration of phthalate esters in the water in contact with PET and PET/nanoclay was measured by gas chromatography (GC-FID) combined with the directly suspended droplet microextraction method. Good precision, accuracy and reproducibility over a wide linear range were achieved by the proposed technique under optimal conditions. The experimental results reveal that adding nanoclay fillers to the PET decreases the release of the above-mentioned chemicals from PET into the water considerably due to attainment of a tortuous diffusive path. Data also indicate the significant effect of nanoclay volume fraction and exfoliated morphology on obtaining efficient barrier properties. Furthermore the effects of parameters such as storage time, temperature, and amount and type of nanoclay inclusions were studied on the migration rate, as well.

Free-radical polymerization of polyethylene glycol methyl ether methacrylate macromer (PEGMEMA) was studied in aqueous media and in the presence of potassium persulfate (KPS) as water soluble initiator. An on-line nuclear magnetic resonance (NMR) method was applied to record the reaction data and determine the monomer conversion at various times during the polymerization reaction progress. 1H NMR spectrum of reaction mixture containing monomer, initiator and resultant polymer was continuously recorded in NMR instrument with the increase of reaction time. By processing the obtained data from NMR spectrum, the rate equation can be derived and reaction order can be determined with regard to monomer and initiator concentration. In other words, to determine the order of polymerization with regard to the concentration of reactants in free-radical polymerization of PEGMEMA, macromer samples with different amounts of monomer and KPS were prepared and polymerized at 50 °C. Orders of reaction with respect to monomer and initiator molar concentrations were equal to 1.025 and 0.480, respectively. The obtained values for reaction orders in this study were consistent with the classical kinetic rate equation in which the dependency of polymerization rate (R p) on monomer and initiator concentrations was equal to 1 and 0.5, respectively. To measure polymerization activation energy (E a), the effect of reaction temperature on the polymerization rate was investigated and E a = 37.08 kJ/mol was obtained at the temperature range of 40–50 °C.

Three different forms of natural rubber: maleated natural rubber (MNR), epoxidized natural rubber (ENR) and natural rubber-graft-poly(methyl methacrylate) (NR-g-PMMA) were prepared. Degree of functional groups in rubber molecules was quantified using the integrated peak areas of 1H NMR. It was found that the modified rubbers with similar level of functionality had been successfully prepared. Thermoplastic natural rubber (TPNR) based on blending of thermoplastic polyurethane (TPU) and various forms of rubber were then prepared using melt blending method. The properties of the blends were studied and compared together in relation to different types of natural rubbers prepared (i.e., unmodified NR, MNR, ENR and NR-g-PMMA). It was found that the blends with modified NR exhibited superior stiffness, entropy effect and damping factor compared to other blends with unmodified NR. This is attributed to the chemical interaction between the functional groups of modified NR molecules and polar functional groups in TPU molecules which facilitated higher interfacial adhesion between both phases. The chemical interaction was verified by ATR-FTIR and TSSR techniques. It was also found that the MNR/TPU blend showed the highest tensile modulus, mechanical and elastic properties with smallest and finer grain dispersion of co-continuous phase compared to ENR/TPU, NR-g-PMMA/TPU and unmodified NR/TPU blends, respectively. This might be due to higher chemical interactions between MNR and TPU phases. Furthermore, the incorporation of rubber did reduce hardness (i.e., <60 Shore A) with improvement of elasticity of the blends compared with the original TPU (i.e., ~85 Shore A).

Observations are reported on isotactic polypropylene in uniaxial tensile relaxation tests on specimens subjected to tension up to various maximum strains and retraction down to various stresses. Noticeable evolution of shapes of relaxation curves under retraction is revealed with stress at the beginning of relaxation process: with a decrease in this stress, relaxation diagrams characterized by a monotonic decay of stress with time (simple relaxation) become, first, non-monotonic (mixed relaxation), and, finally, monotonically increasing (inverse relaxation). A thorough investigation is performed on the effect of multi-cycle preloading (maximum strain per cycle, minimum stress per cycle, number of cycles, and strain rate) on transition from simple to mixed and to inverse relaxation. It is found that (1) intensity of mixed relaxation increases with maximum strain when this parameter remains below the yield strain and decreases in the post-yield region of deformations, (2) an increase in number of cycles under preloading leads to reduction of intensity of mixed relaxation and transition from mixed to inverse relaxation, (3) inverse relaxation diagrams of specimens subjected to the same preloading program with various strain rates can be superposed to construct a master-curve. A constitutive model is developed in cyclic viscoelastoplasticity of semicrystalline polymers. A polymer is thought of as two-phase continuum composed of amorphous and crystalline regions. Both phases were treated as viscoelastoplastic media whose response was governed by different kinetic equations for evolution of plastic strains and different kinematic equations for changes in relaxation rates and relaxation spectra driven by plastic flow. Good agreement is demonstrated between the experimental data in relaxation tests under retraction and the results of numerical simulation.

In this study, chitosan/polylactide scaffolds reinforced with nano-calcium phosphate (average crystallite size of 16.5 nm) (CP) were fabricated to create a material with excellent properties for bone tissue engineering applications via freeze-casting method. The structural and mechanical properties of nanocomposite scaffolds were studied by increasing amount of chitosan/poly lactide ratio and nano-CP content in both dry and hydrate states, which reflected the exact status of scaffolds in a real biomechanical environment. The morphologies of the nanocomposite scaffolds were viewed using scanning electron microscopy (SEM) and all the scaffolds exhibited a high porosity (up to 92 %) with open pores of 38–387 μm average diameters, which decreased with increased chitosan/polylactide ratio and nano-CP content. Also, SEM photograph of the cross-sectional area of the scaffold showed nano-CP was dispersed all over the polymer matrix thoroughly. The results of mechanical tests showed that the compressive modulus (E) and compressive stress (σ) enhanced, when chitosan and nano-CP increased. X-ray diffraction analysis indicated typical chitosan, polylactic acid and nano-CP peaks and showed that the increase in nano-CP weight percentage increased its peak intensities. In addition, the effect of pore-size distributions of the scaffolds with the same composition was studied in relation to mechanical properties. The results showed substantial differences in the pore-size distributions of scaffolds with the same composition prepared, which have no effect on their dry states.

A novel dicarboxyl-terminated poly(2,2,3,4,4,4-hexafluorobutyl acrylate) oligomer (CTHFA) was synthesized through metal-free anionic polymerization and hydrolysis reaction. Chemical structures of CTHFA were characterized by gel permeation chromatography and 1H NMR. Two types of CTHFA with different chain lengths were initially used as an efficient surface modifier to improve the surface properties of epoxy resin, at the content of CTHFA ranging between 0 and 8 wt%. We minimized the amounts of the CTHFA used to achieve a high hydrophobic surface that was not obviously affected by the thermal properties of the epoxy resin. Surface properties and surface composition of the designed fluorinated epoxy resin were investigated by the contact angle and X-ray photoelectron spectroscopy (XPS). Modified epoxy resin with 5 wt% CTHFA containing longer chain length showed excellent hydrophobic surface properties (a high water contact angle about 115° and low surface energy 14.12 mN/m2) while the modified epoxy resin with 5 wt% CTHFA containing shorter chain length did not. XPS analyses indicated that the 5 wt% of fluorinated CTHFA epoxy resin with long macromolecular-chain enhanced more fluorinated groups’ migration to the surface than the fluorinated CTHFA-modified epoxy resin with short macromolecular-chain at the same content. Moreover, thermal properties of CTHFA-modified epoxy resin were also investigated.

A polyacrylic high oil-adsorption resin was prepared by a suspension polymerization method with butyl acrylate and methyl methacrylate as monomers, benzoyl peroxide as an initiator, poly(vinyl alcohol) (PVA-1788) as a dispersing agent, and divinyl benzene as a cross-linking agent. The effects of dispersing agent, pore-forming agent and cross-linking agent on resins structures were revealed. The maximum specific surface areas and pore volumes of the resulting resins were 853.8 m2/g and 1.188 cm3/g, respectively. These structural parameters endowed excellent adsorbability to the resins. Abamectin, a macrolide insecticide, was selected as a model pesticide, and cyclohexanone was investigated as solvent in adsorption tests. The adsorption isotherms illustrated that adsorption was an endothermic process, and the optimum adsorption temperature was 293 K. Fourier transform infrared spectroscopy, thermogravimetric analysis, and X-ray diffraction results suggested that abamectin-loaded resins were prepared. The sustained release data indicated that the pesticide-loaded resins exhibited a sustained pesticide release pattern, and the releasing process continued over 15 days in an alcohol medium with the final release rate of over 90 %. These studies established a theory and experimental foundation for the actual application of this method. Meanwhile, the pesticide-loaded resins could be applied to actual production process by adding proper adjuvants in their compositions.

A UV-resistant PBO fiber containing light stabilizer OB-1(2,2′-(1,2-ethenediyldi-4,1-phenylene) bis-benzoxazole) is reported. OB-1/PBO Fiber, which had excellent mechanical properties as PBO was prepared via in situ polymerization and dry-jet wet-spinning technique. Effects of the light stabilizer (OB-1) on UV stability of PBO fiber and possible degradation mechanism were investigated by tensile testing, intrinsic viscosity measurement, SEM, and ATR-FTIR analysis. Under UV-accelerated aging, the tensile strength of PBO fiber declined sharply. After exposed to UV 340-nm light for 310 h, the strength retention was only 44.17 %. SEM analysis showed the smooth and compact surface with well-oriented microfibrils was damaged. Meanwhile, the photostability of PBO fiber could be enhanced greatly by adding a small amount (0.05–0.2 %) of OB-1. Under the same conditions, the strength retention of 0.2 %OB-1/PBO fiber increased to 64.84 %, which was 47 % higher than that of PBO fiber. SEM observation showed the surface of OB-1/PBO fiber was also damaged, but it was not as so severe as PBO fiber. After UV irradiation, the intrinsic viscosity of PBO and OB-1/PBO fiber decreased which implies that mild chain scissions occurred. ATR-FTIR analysis revealed that oxazole rings in PBO and OB-1/PBO backbone were disrupted and formed amide linkages. These results indicated the loss of strength is mainly due to the break of microfibrils and fiber morphology, mild chain scission, and the disruption of oxazole rings.