Oxidative degradation of poly (vinyl acetate) and poly (ε-caprolactone) and their mixtures in solution

The oxidative degradation of the poly (ε-caprolactone) (PCL), poly (vinyl acetate) (PVAC) and their mixtures in dichlorobenzene has been investigated at various temperatures (70-130°C) in the presence of benzoyl peroxide. The interaction between the polymers is quantified by monitoring the molecular weights of individual polymers using gel-permeation chromatography. The various physical mixtures employed in the present investigation are , and wt%/wt% PCL/PVAC. Experimental data indicated that the degradation is random without cross-linking and repolymerization. An optimum in degradation temperature (corresponding to maximum degradation rate) of 105°C was observed for the entire range of polymer compositions (0-100% PCL) investigated. This optimum temperature of degradation is characteristic mostly of the initiator and only to a small extent of the degrading polymer system. The experimental results of the mixtures indicated that the degradation rates of PVAC are significantly enhanced, while the degradation rates of PCL are decreased in the physical mixture. This can be attributed to the proton-accepting and proton-donating nature of PCL and PVAC, respectively. A radical mechanism for the oxidative degradation of pure polymers and their mixtures has been proposed and a model based on continuous distribution kinetics was developed considering the interaction of the polymers through hydrogen abstraction and the parameters were evaluated numerically. The activation energies for the peroxide attack for the PCL and PVAC are 10.5 and , respectively. The activation energies for the random chain scission of PCL and PVAC are 10.6 and , respectively.     

Compatibilisation of blends of poly(vinyl chloride) and poly(styrene-block-(ethylene-co-butadiene)-block–styrene) with maleic anhydride grafting

Abstract

The mechanical properties of blends of poly (vinyl chloride) (PVC) and poly (styrene-block-(ethylene-co-butadiene)-block–styrene) (SEBS) were investigated using maleic anhydride grafted SEBS (SEBS-g-MAH) as a compatibiliser. The results indicated that addition of a small amount of SEBS-g-MAH during melt blending significantly improved the mechanical properties of PVC/SEBS blends. The impact strength of the compatibilised PVC/SEBS blends was found to reach a maximum of 53·5±2·78 KJ m^?2 at room temperature and a maximum of 32·8±1·66 KJ m^?2 at ?20°C at an SEBS-g-MAH loading level of 6 phr. The two glass transition temperatures of the components in the blends converged to some degree upon addition of SEBS-g-MAH for compatibilisation. At room temperature the dynamic storage modulus of the compatibilised blends was higher than that of the blends without compatibilisation. The size of the dispersed phase domains in the blends was appreciably reduced on addition of SEBS-g-MAH during melt blending according to scanning electron microscopy. All the above observations revealed that SEBS-g-MAH enhanced the compatibility between PVC and SEBS in the PVC/SEBS blends.     

Health and environmental effects of phthalate plasticisers for poly(vinyl chloride) – an update

Abstract

The established information is summarised and used together with the latest research findings to present a current understanding of the health and environmental effects of phthalates. It is concluded that the carcinogenic and reproductive effects produced by phthalates in rodents are species specific and of little relevance to humans. The environmental impact of phthalates is considered to be low due to their ready biodegradability and low toxicity.     

Impact strength and morphology in poly(vinyl chloride) window profiles –relationship with gelation level

Abstract

The impact strength resistance of extruded PVC window profiles is a result of the combined effects of the interaction of their intrinsic material properties and processing/fabrication variables. Intrinsic variables include all the components of the formulation, such as the type and level of impact modifier and filler. As such, an appropriate level of toughness can be achieved by selecting the type and amount of rubber particles present in the matrix. However, the impact properties of poly(vinyl chloride) (PVC) profiles are also drastically affected by the thermal and shear history of the PVC matrix. The effect of processing on mechanical properties is explored by altering the temperature profile set on the extruder, and by varying the shear heating phenomena using different lubrication balances. The gelation level of any PVC formulation tends to increase with the level of work on the material, i.e. with increased melt temperature and shear history. The study reported in the present paper is intended to quantify the degree of fusion of the primary crystallites as a function of the melt temperature, and show the dependence of the toughness of the extruded profiles on the resulting free volume. Free volume in PVC extruded profiles depends on the degree of the gelation of the matrix and also on the cooling rate of the melt. As extrusion output increases, cooling of the melt is so fast that polymer chains have much less time to recover and reach a state of minimum entropy. Upon physical aging, the free volume tends to decrease. The reduction in free volume changes the non-equilibrium state of the glass phase, thus reducing the toughness of the material, and causing embrittlement under certain test conditions.

Finally, the effect of filler level and type of impact modifier (two intrin sic variables) on the impact strength of extruded profiles with various levels of free volume are presented.     

Dielectric relaxation and Poole–Frenkel conduction in poly(vinyl chloride) blends with bisphenol A/Egyptian corncob resin

The dielectric constant (ε′), dielectric loss index (ε″), direct-current conductivity, and current–voltage (I–V) characteristics of pure poly(vinyl chloride) (PVC) and blends of PVC and bisphenol A/Egyptian corncobs (BCC) were investigated at different temperatures. The relaxation processes for PVC and its blends revealed that PVC and BCC had an incompatible phase. PVC blends with 5 wt % BCC exhibited a peculiar I–V behavior. Both ε′ and ε″ were used to study miscibility and phase behavior in blends of PVC. The activation energies of all PVC samples were calculated. At higher voltages, the conduction mechanism could be identified as the Poole–Frenkel type. In addition, the ionic groups of BCC could enhance the PVC conductivity. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Hard coatings on polycarbonate plate by sol–gel reactions of melamine derivative,poly(vinyl alcohol), and silicates

Hard coatings were deposited on a polycarbonate plate using a sol–gel process with a melamine derivative, poly(vinyl alcohol) (PVA), and silicates and examined as potential substitutes for glass in cars. PVA was partially functionalized with (3-isocyanatopropyl)triethoxysilane, and the synthesized polymer was used to form a coating solution with methylated poly(melamine-co-formaldehyde), tetraethoxysilane, and methyltriethoxysilane. The coatings that contained both the melamine and silicate structures were deposited using a sol–gel process. The optimum conditions and formulation to obtain excellent physical properties of the coating were determined. Smooth coatings with the hardness of a 3H class pencil, excellent abrasion resistance and transparency were formed.     

A Hybrid Membrane of Poly(vinyl alcohol) and Phosphotungstic Acid for Fuel Cells

Proton conducting membranes composed of phosphotungstic acid (PWA) and poly(vinyl alcohol) (PVA) were prepared. Conductivity and Fourier transform infrared spectrometer(FTIR) measurements show that most of the acid embedded are stable in the PVA matrix when the membrane is immerged in water or methanol solution at room temperature. Conductivity of the composite membranes scatters around 10-3S·cm-1 at room temperature. The methanol crossover through the membranes is about an order of magnitude lower than that through Nafion 117 membrane.     

A rapid test to measure adhesion between optical fibers and ethylene–vinyl acetate copolymer (EVA)

Optical fibers are transported on a drum and on some occasions it is essential to fix them and to keep them fixed to the drum. Adhesives are used in such situations to obtain the best and durable fixation. This research shows a new approach for the examination of the adhesion effects and forces between the optical fibers and the adhesive during a tensile test. A solution of ethylene–vinyl acetate (EVA) copolymer in toluene was used as the adhesive for optical fibers and applied using specially designed apparatus. The testing procedure consisted of optical fiber characterization using optical microscopy for measurement of geomertrical parameters; tensile test to obtain the strength of adhesion that keeps the fibers together; nanoindentation of the optical final layer; SEM for precise geometry measurements and insight in the adhesive aspect after the test, and FTIR analysis to find out the chemical composition of polymer protective coating to have an obtain information about chemical environment for the adhesive. The optical fiber with outstanding mechanical characteristics was used to examine adhesives. A sample of two fibers connected with EVA was subjected to the tensile test to examine the adhesion forces. Finite element modeling was used to simulate the behavior and stress distribution of the adhesion layer. This method could assist in reaching a conclusion about the quality of the adhesion obtained in an experimental procedure.     

On the association between poly(vinyl alcohol) and sodium dodecyl sulfate and its effect on liquid–liquid interfacial tension: A mathematical model

Association between poly(vinyl alcohol-co-vinyl acetate) copolymer (PVA) and sodium dodecyl sulfate (SDS) was studied experimentally and theoretically. It was found that, for the ethyl acetate-aqueous phase interface in which PVA was previously adsorbed, the interfacial tension (γ) increases abruptly to a maximum and then exhibits a relatively mild decay with the addition of SDS to the aqueous phase. The theoretical results indicate that vinyl acetate (VAc) segments determine γ. However, for relatively low concentrations of SDS (C_SDS), this latter plays a major role because through its association with the VAc segments it modulates the extent to which PVA is adsorbed at the interface, indirectly determining the value of γ. As C_SDS approaches to the CMC value for SDS, its influence on γ decreases because SDS tends to self-assembly rather than associates with VAc. These model predictions are consistent with experimental findings reported in the literature.     

Biaxial orientation of poly(vinyl chloride) compounds Part 2 –Structure–property relationships and their time dependency

Abstract

X-ray diffraction and thermomechanical analysis have been used, respectively, to examine structural order and shrinkage behaviour for oriented samples of rigid and flexible poly(vinyl chloride) (PVC). Results were compared with previously measured tensile properties and structure–property relationships explored. X-ray diffraction showed that drawing produces planar crystallite orientation in PVC sheets. If drawing and subsequent annealing conditions are held constant, but draw ratio is varied, there is good correlation between structural order measured by X-ray diffraction and tensile strength. Increased annealing time and temperature improve crystallite order and dimensional stability, while tensile strength is unchanged. The greatest enhancement in tensile strength is achieved by stretching PVC towards its maximum draw ratio at 90°C, but optimum thermal stability of the oriented structure is achieved when higher annealing temperatures are used. Room temperature recovery is observed for flexible PVC when the material has a glass transition temperature below ambient. This can be delayed by increased annealing time and temperature, and by increased draw ratio.     

Graphene incorporated poly(vinyl chloride) composites prepared by mechanical activation with enhanced electrical and thermo–mechanical properties

This study reports the improvement in electrical and thermomechanical properties of pristine poly(vinyl chloride) (PVC) by the incorporation of graphene (GN) resulting in GN/PVC composites 137 mechanical activation (MA) using dioctyl phthalate (DOP) as dispersant. Microstructure, electrical, and thermomechanical properties of GN/PVC were systematically investigated. Scanning electron microscopy, mercury intrusion porosimetry, and particle size distribution analysis revealed that high-energy ball milling destroyed the structure of pristine PVC and GN, without any visible agglomeration of GN in the resulting GN/PVC composites. At 0.13 wt% GN loading, the surface resistivity of GN/PVC composites was less than 3 × 10⁸ Ω/square, meeting requirements of commercial antistatic PVC materials. Moreover, GN/PVC composites showed enhanced mechanical properties, thermal stability, and glass transition temperature than pristine PVC. Credited to enhanced thermomechanical and electrical properties of the newly designed GN/PVC composites, they could be deemed as potential alternative to classical PVC-based antistatic materials in targeted applications. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48375.     

Poly(acrylic acid)/poly(vinyl alcohol) compositions coaxially electrospun with poly(?-caprolactone) and multi-walled carbon nanotubes to create nanoactuating scaffolds

Skeletal muscle regeneration usually causes scar tissue formation and loss of function, an alternative method is needed. In this study, poly(?-caprolactone), multi-walled carbon nanotubes, and (83/17, 60/40, 50/50, and 40/60) poly(acrylic acid)/poly(vinyl alcohol) (PCL-MWCNT-PAA/PVA) were coaxially electrospun to create scaffolds. All four were conductive; however, not all scaffolds actuated when electrically stimulated. The best response occurred when 20 V was applied. A biocompatibility study where skeletal muscle cells were exposed to 0, 0.14%, and 0.7% MWCNT showed that these concentrations were low enough to not cause harm over a four week period. All scaffolds were biocompatible but, the 40/60 scaffolds had more cells. Fluorescent staining showed large clusters of multinucleated cells with actin interaction. Although scaffold tensile properties are greater than skeletal muscle, our other results show that with more modification to cause contraction instead of bending this combination of materials may show promise as components in an artificial muscle.     

Experimental electrohydrodynamics of poly(γ-Benzyl-L-Glutamate) in M-Cresol solution subjected to shear flow and electric fields

Electrohydrodynamics of a dilute solution of rigid macromolecules was experimentally studied in a continuation of previous theoretical work. We used poly(γ-benzyl-L-glutamate), having 4 different molecular weights ranging from 15,000 to 236,000, dissolved in m-cresol. Poly(γ-benzyl-L-glutamate) solutions were subjected to combinations of simple shear flow field and uniform electric field perpendicular to the shear direction. Transient birefringence and extinction angle were simultaneously measured using the phase-modulated birefringence method. Steady state results were compared with the theoretical prediction from previous works and rotational difiusivity and permanent dipole strength of PBLG were obtained from multiple parameter fitting. Consequently, the optical state of PBLG solution could be explained to a certain extent by the dimensionless field parameters established in the previous theory.     

A facile and green method for the production of novel and potentially biocompatible poly(amide-imide)/ZrO2–poly(vinyl alcohol) nanocomposites containing trimellitylimido-l-leucine linkages

We have reported the synthesis of nanocomposites (NCs) based on chiral poly(amide-imide) (PAI) and modified zirconium nanoparticles (ZrO₂ NPs) with poly(vinyl alcohol) (PVA). The optically active PAI was prepared under the green condition via the direct polycondensation of biocompatible trimellitylimido-l-leucine diacid and 4,4′-diaminediphenylsulfone in the presence of tetrabutylammonium bromide and triphenyl phosphite as the green solvent and the activating agents. NPs, due to a high surface to volume ratio, have a great tendency to agglomerate in the polymer matrix. So, at first, the surface of ZrO₂ NPs was modified with the PVA as the biodegradable and biocompatible polymer. Afterward, the modified NPs were added into the PAI matrix in the ethanol solution under ultrasonic irradiations. The obtained PAI/ZrO₂–PVA NCs (PZ–PNC)s were characterized by various techniques. The Fourier transform infrared proved the formation of PZ–PNCs. Field emission-scanning electron microscopy exhibited that ZrO₂ NPs had good dispersion in the PAI matrix, and transmission electron microscopy indicated that ZrO₂ NPs were coated by a nanometer-thick layer of PVA that was about 10 nm. X-ray diffraction analysis showed that the ZrO₂ NPs retained their crystalline structure after they were added in the PAI matrix. Thermogravimetric analysis illustrated that the prepared PZ–PNCs had a better thermal stability than the neat PAI.     

A randomly branched poly(hydroxyl-β-amino amide): synthesis and complexation

A novel type of polycation with high density of discrete charge, diversified amino group type and abundant hydrophilic short-chains was synthesized from tetraethylenepentamine (TEPA) and glycidol acrylate. The obtained polycation was abbreviated as PTGA. The structure and protonation property of PTGA was characterized by ¹H NMR, FTIR, GPC and acid-base titration. ¹H NMR of PTGA indicated that there were not only Michael addition and ring-opening but also high degree of amidation during polymerization. Only 12% ester group was left after polymerization. So PTGA is a kind of poly(hydroxyl-β-amino amide). Acid base titration indicated that the protonation of PTGA has wide protonation range and shows obvious proton sponge effect. The complexation of PTGA with polyanion was studied by using poly(acrylic acid) (PAA) as a model polyanion. The complex was characterized by dynamic light scattering and UV-Vis spectroscopy. It was found that the size of complex particle size first increased and then decreased as the charge ratio of PTGA to PAA.     

Interaction between gold (III) chloride and potassium hexacyanoferrate (II/III)—Does it lead to gold analogue of Prussian blue?

Prussian blue analogues are a class of compounds formed by the reaction between metal salt and potassium hexacyanoferrate (II/III). In our earlier report, the formation of Au@Prussian blue nano-composite was noticed on potential cycling the glassy carbon electrode in a medium containing gold (III) chloride and potassium hexacyanoferrate (III). Hence in this work, the formation of gold hexacyanoferrate was attempted by a simple chemical reaction. The reaction of gold (III) chloride with potassium hexacyanoferrate (II/III) was examined by UV–Vis spectroscopy and found that there is no redox reaction between gold (III) chloride and potassium hexacyanoferrate (III). However, the redox reaction occurs between gold (III) chloride and potassium hexacyanoferrate (II) leading to the formation of charge transfer band and the conversion of hexacyanoferrate (II) to hexacyanoferrate (III) was evidenced by the emergence of new absorption peaks in UV–Vis spectra. The oxidation state of gold in Au–Fe complex was found to be +1 from X-ray photoelectron spectroscopy. The stability of the Au–Fe complex was also studied by cyclic voltammetry. Cyclic voltammetric results indicated the presence of high spin iron in Au–Fe complex. Hence ‘as formed’ Au complex may be KFe_x[Au(CN)₂]_y. The results revealed that the formation of gold hexacyanoferrate was not feasible by simple chemical or electrochemical reaction in contrast to other Prussian blue analogues.     

Suprarmolecular hydrogels driven by the dual host–guest interactions between α-cyclodextrin and ferrocene-modified poly(ethylene glycol) with low-molecular-weight

In general, α-cyclodextrin (α-CD) and low-molecular weight poly(ethylene glycol) (low-MW PEG) (M_w = 400–10,000) cannot construct supramolecular hydrogels but easily form crystalline precipitates. In this study, low-MW PEG (M_n = 2000, PEG-2000) was functionalized by ferrocene as mono-end-group. The obtained ferrocene-modified PEG-2000 (FcPEG-2000) further self-assembled into supramolecular hydrogel with α-CD even at low concentration (C_FcPEG-2000 = 17 mg/ml), driven by dual host–guest interaction between α-CD and FcPEG-2000. Interestingly, the hydrogel was still observed even when hydrophobic Fc group was oxidized to hydrophilic ferrocenium (Fc⁺) or included into the cavity of β-CD. In the former case, the existence of Fc⁺ end groups is considered to decrease the probability of PEG de-penetration from α-CD cavity, so that α-CDs have more location and opportunities to aggregate into more channel-type crystalline domains as physical cross-linking points. While in the later case, the synergistic effect of host–guest interaction between β-CD and ferrocenyl groups and host–guest interaction between α-CD and PEG chains are considered to be the main reason. The resultant FcPEG-2000 based hydrogels showed the property of shear-thinning.     

A new extra situ sol–gel route to silica/epoxy (DGEBA) nanocomposite. A DTA study of imidazole cure kinetic

Silica nanoparticles were obtained through the Stöber method, from mixtures of tetraethoxysilane (TEOS) and 3-aminopropyltriethoxysilane (APTS). The nanoparticles were dispersed in tetrahydrofuran (THF) and coupled to bisphenol A epoxy resin (DGEBA) through surface amino groups. After removing THF non-isothermal cure was performed at different heating rates (2–20°C/min), using imidazole (2–4 wt%) as curing agent. For the sake of comparison bare DGEBA epoxy polymers were also prepared with similar schedule A nanocomposite of well-dispersed silica nanoparticles (5 wt%) in a fully cured epoxy matrix was easily obtained. Lower cure kinetics were observed with silica addition. This was attributed to reduction of the imidazole volume concentration. Cure activation energy was not influenced by silica presence, whereas it changed with the imidazole content. Therefore, experimental results suggested that silica had only an indirect effect (the reduction of the imidazole molar concentration) on the epoxy matrix cure kinetics. Glass transformation temperatures, T _g, as high as 175°C were recorded. The nanocomposite glass transformation temperature depended on the heating rate of the cure process, the imidazole and silica content. T _g changes as high as 40°C were detected as a function of the heating rate. At higher imidazole content no differences in T _g values between bare polymer and the nanocomposite were observed. This suggests that a higher imidazole content assures a better interconnection between the compatibilizing epoxy shell around the nanoparticles and the epoxy matrix. The new proposed methodology is an easy route to engineer both nanocomposites structure and interfacial interactions, thus tailoring their properties.     

Polymer–lipid interactions: Biomimetic self-assembly behaviour and surface properties of poly(styrene-alt-maleic acid) with diacylphosphatidylcholines

Various lubricating body fluids at tissue interfaces are composed mainly of combinations of phospholipids and amphipathic apoproteins. The challenge in producing synthetic replacements for them is not replacing the phospholipid, which is readily available in synthetic form, but replacing the apoprotein component, more specifically, its unique biophysical properties rather than its chemistry. The potential of amphiphilic reactive hypercoiling behaviour of poly(styrene-alt-maleic acid) (PSMA) was studied in combination with two diacylphosphatidylcholines (PC) of different chain lengths in aqueous solution. The surface properties of the mixtures were characterized by conventional Langmuir–Wilhelmy balance (surface pressure under compression) and the du Noüy tensiometer (surface tension of the non-compressed mixtures). Surface tension values and ³¹P NMR demonstrated that self-assembly of polymer–phospholipid mixtures were pH and concentration-dependent. Finally, the particle size and zeta potential measurements of this self-assembly showed that it can form negatively charged nanosized structures that might find use as drug or lipids release systems on interfaces such as the tear film or lung interfacial layers. The structural reorganization was sensitive to the alkyl chain length of the PC.     

Zwitterionic polymer-coated porous poly(vinyl acetate–divinyl benzene)microsphere: A new support for enhanced performance of immobilized lipase

Enzyme immobilization has attracted great attention for improving the performance of enzymes in industrial applications. This work was designed to create a new support for Candida rugosa lipase(CRL) immobilization.A porous poly(vinyl acetate–divinyl benzene) microsphere coated by a zwitterionic polymer, poly(maleic anhydride-alt-1-octadecene) and N,N-dimethylethylenediamine derivative, was developed for CRL immobilization via hydrophobic binding. The catalytic activity, reaction kinetics, stabilities and reusability of the immobilized CRL were investigated. It demonstrated the success of the zwitterionic polymer coating and subsequent CRL immobilization on the porous microsphere. The immobilized lipase(p2-MS-CRL) reached27.6 mg·g~(-1) dry carrier and displayed a specific activity 1.5 times higher than free CRL. The increase of Vmax and decrease of Kmwere also observed, indicating the improvement of catalytic activity and enzyme-substrate affinity of the immobilized lipase. Besides, p2-MS-CRL exhibited significantly enhanced thermal stability and p H tolerance. The improved performance was considered due to the interfacial activation regulated by the hydrophobic interaction and stabilization effect arisen by the zwitterionic polymer coating. This study has thus proved the advantages of the zwitterionic polymer-coated porous carrier for lipase immobilization and its potential for further development in various enzyme immobilizations.