PRESSURE-SENSITIVE ADHESION IN THE BLENDS OF POLY(N-VINYL PYRROLIDONE) AND POLY(ETHYLENE GLYCOL) OF DISPARATE CHAIN LENGTHS

Adhesive behavior in blends of high molecular weight poly(N-vinyl pyrrolidone (PVP) with a short-chain, liquid poly(ethylene glycol) (PEG) has been studied using a 180° peel test as a function of PVP-PEG composition and water vapor sorption. Hydrophilic pressure-sensitive adhesives are keenly needed in various fields of contemporary industry and medicine, and the PVP-PEG blends, pressure-sensitive adhesion has been established to appear within a narrow composition range, in the vicinity of 36 wt% PEG, and it is affected by the blend hydration. Both plasticizers, PEG and water, behave as tackifiers (enhancers of adhesion) in the blends with glassy PVP. However, PEP alone is shown to account for the occurrence of adhesion, and the tackifying effect of PEG is appreciably stronger than that of sorbed water. Blend hydration enhances adhesion for the systems that exhibit an apparently adhesive type of debonding from a standard substrate (at PEG content less than 36 wt%), but the same amounts of sorbed water are also capable of depressign adhesion in the PEG-overloaded blends, where a cohesive mechanism of adhesive joint failure is typical. The PVP-PEG blend with 36% PEG couples both the adhesive and cohesive mechanisms of bond rupture (i.e., the fibrillation of adhesive polymer under debonding force and predominantly adhesive locus of failure). Blend hydration effect on adhesion has been found to be reversible. The micromechanics of adhesive joint failure for PVP-PEG hydrogels involves the fibrillation of adhesive polymer, followed by fibrils stretching and fracturing as their elongation attains 1000-1500%. Peel force to rupture the adhesive bond of PVP-PEG blends increases with increasing size of the tensile deformation zone, increasing cohesive strength of the material, and increasing tensile compliance of the material, obeying the well-known Kaelble equation, derived originally for conventional rubbery pressure-sensitive adhesives. The major deformation mode upon peeling the PVP-PEG adhesive from a standard substrate is extension, and direct correlations have been established between the composition behaviour of peel strength and that of the total work of viscoelastic strain to break the PVP-PEG films under uniaxial drawing. As a result of strong interfacial interaction with the PET backing film, the PVP-PEG adhesive has a heterogeneous two-layer structure, where different layers demonstrate dissimilar adhesive characteristics.     

The effect of deformation on the phase separation in the polycapramide-caprolactam system

The phase state and phase transitions in melts and solutions of polycapramide (PCA) in caprolactam were studied by means of viscosimetry, optical interferometry, and polarization microscopy. It has been shown that the orientation of macromolecules of PCA in the flow zone results in the expansion of the area of immiscibility in the phase diagram. The isothermal crystallization was traced by the change of the length of the induction period by means of viscosimetry measurements. The dependence of the rate of isothermal crystallization on the rate of shear deformation is quite marked. The decrease of the rate of crystallization at high rates of shear is believed to be associated with the destruction of critical-size nuclei in a high velocity gradient stream.     

Effect of water on the strength of rubber bonding with adhesives based on reactive oligomers

The effect of water redistribution between SKEPT-40 rubbers and reactive adhesives based on SKN-18KTR mixtures with ED-20 on the strength of adhesive compositions was studied. Water vapor sorption isotherms were measured. It was shown that the water content of rubbers during their scheduled conditioning at a humidity of 65–70% leads to the spontaneous redistribution of water between the substrate and the adhesive. This process is accompanied by the retardation of the formation of the adhesive network structure and, as a consequence, by a fall in the strength of adhesive joints. The mechanism of formation and failure of SKEPT-40-(SKN + ED-20) adhesive joints was revealed. A procedure for calculating the amount of water capable of redistributing between the elements of adhesive joints is proposed. Rubber conditioning parameters that ensure the required quality of bonding the rubbers with SKN-18KTR-ED-20 compositions were determined.     

Palladium-containing hypercrosslinked polystyrene as an easy to prepare catalyst for Suzuki reaction in water and organic solvents

A simple and rapid procedure for the incorporation of nanosized Pd particles into hypercrosslinked polystyrene matrix was developed. The prepared catalyst has shown high activity in the coupling of aryl bromides and chlorides with phenylboronic acid, with water being the preferred solvent. The catalyst can be recycled two times without loss of activity.     

Study of Fractal Characteristics of Individual Macromolecular Tangles

Protection of Metals and Physical Chemistry of Surfaces - The fractal characteristics of individual macromolecular tangles of block and random copolymers are investigated. It was found that the...     

The Performance of Insulating Tapes and Wrappers

Protection of Metals and Physical Chemistry of Surfaces - The kinetics of water vapor permeability of insulating tapes of the Polyen, Poliken, Nitto, and Furukawa series was studied by the...     

Transmission electron microscopy study of the heavy-ion-irradiation-induced changes in the nanostructure of oxide dispersion strengthened steels

Transmission electron microscopy was used to study the effect of heavy-ion irradiation on the structure and the phase state of three oxide dispersion strengthened (ODS) steels: ODS Eurofer, ODS 13.5Cr, and ODS 13.5Cr–0.3Ti (wt %). Samples were irradiated with iron and titanium ions to fluences of 10¹⁵ and ~3 × 10¹⁵ cm^–2 at 300, 573, and 773 K. The study of the region of maximum radiation damage shows that irradiation increases the number density of oxide particles in all samples. The fraction of fine inclusions increases in the particle size distribution. This effect is most pronounced in the ODS 13.5Cr steel irradiated with titanium ions at 300 K to a fluence of 3 × 10¹⁵ cm^–2. It is demonstrated that oxide inclusions in ODS 13.5Cr–0.3Ti and ODS 13.5Cr steels are more stable upon irradiation at 573 and 773 K than upon irradiation at 300 K.     

Thermodynamic analysis of the phase equilibrium of the polystyrene-poly(vinyl methyl ether) system

The phase diagrams of polystyrene (PS)-poly(vinyl methyl ether) (PVME) system obtained via optical interferometry in the study of polymer interdiffusion are presented. The influence of molecular weight of the PS on the position of the binodal curve dome and the critical point is shown. Paired interaction parameters and their temperature dependences are calculated in the framework of Flory-Huggins theory both for the present experimental diagrams and for the ones, previously obtained by different authors. It is shown that the generalized temperature dependence of the Flory-Huggins parameter can be used to model phase equilibrium in a wide range of temperatures and compositions. For the first time for PS-PVME system, the generalized phase state diagram characterized by both lower and upper critical solution temperatures is calculated and constructed.