Effect of organoclay on the physical properties of UV-curable coatings

The combination of UV-curing and nanocomposite technology has been studied to produce cost-effective coatings with superior physical and mechanical properties. The clay was modified with dimethyl dihydrogenated-tallow quaternary ammonium salt and made organophilic. The effect of the organoclay(2-10 phr) on curing rate, mechanical, thermal and physical properties of a urethane-acrylate coating has been determined. X-ray diffraction analysis, AFM, SEM and TEM images as well as the tensile properties of different formulations have confirmed the uniform distribution of organoclay in polymer matrix. At 3 phr organoclay addition, the UV-cured film exhibited the best mechanical performance due to the formation of both intercalated and exfoliated morphologies. Curing time was reduced and the initial thermal decomposition temperature shifted 50°C to higher temperature by the incorporation of small amount of organoclay. The nanocomposite coating was also found to be more resistant against scratching compared with clay-free coating

Investigation of barrier properties of as cast and biaxially stretched pet/evoh and peti/evoh blend films

In this study, poly(ethylene terephthalate)(PET)/poly(ethylene-co-vinyl alcohol)( EVOH) (95/5 w/w) and poly(ethylene terephthalate-co-isophthalate) random copolymer containing 10 wt.% isophthalic acid (PETI)/EVOH (95/5 w/w) blends have been prepared with compatibilizer types as poly(ethylene terephthalate)-cosulfonated isophthalate (PET-co-SIPA), glycol modified poly(ethylene terephthalate) (PETG) and hydroxyl-terminated polybutadiene (HTPB) by using a co-rotating intermeshing twin screw extruder. Cast films have been stretched simultaneously and biaxially 2 and 3 times their original dimensions (λ=2, λ=3). The effects of biaxial orientation, crystallinity, morphology, and chemistry on oxygen gas permeability were analyzed by using different characterization techniques i.e. scanning electron microscopy (SEM), differential scanning calorimetry (DSC), and gas permeability analyzer. After extrusion, the dispersed phase has a particle size of 0.4-0.8 μm without a compatibilizer. Replacing PET homopolymer with PETI has little effect on particle size of the dispersed phase (0.4-0.5 μm) without using a compatibilizer. The smallest particle size of EVOH was 0.17-0.2 μm for PET blends when employed a hydroxyl terminated polybutadiene (HTPB) and 0.15-0.25 μm (glycol modified PET, PETG) and 0.18-0.26 μm (HTPB) for PETI blends. Oxygen gas permeability of the blend films reduces to some extent after stretching. Nonetheless, an increase in oxygen gas permeability has been observed when the results of the neat PET and PETI taken into consideration. This situation results from low degree of crystallinity of the blends. Casted and oriented PET/EVOH films show decreased water vapor permeability values when compared to that of neat PET. The lowest value has been obtained when employed HTPB as the compatibilizer. Casted films of PETI/EVOH blends have higher water vapor permeability values than that of the neat PETI. Water vapor permeability values decrease when films stretched 2 times and 3 times. Nonetheless, comparison of the results together with that of the neat PETI indicates that water vapor permeability values of the stretched films are almost the same as PETI

A cosolvent surfactant mechanism affects polymer collapse in miscible good solvents

The coil–globule transition of aqueous polymers is of profound significance in understanding the structure and function of responsive soft matter. In particular, the remarkable effect of amphiphilic cosolvents (e.g., alcohols) that leads to both swelling and collapse of stimuli-responsive polymers has been hotly debated in the literature, often with contradictory mechanisms proposed. Using molecular dynamics simulations, we herein demonstrate that alcohols reduce the free energy cost of creating a repulsive polymer–solvent interface via a surfactant-like mechanism which surprisingly drives polymer collapse at low alcohol concentrations. This hitherto neglected role of interfacial solvation thermodynamics is common to all coil–globule transitions, and rationalizes the experimentally observed effects of higher alcohols and polymer molecular weight on the coil-to-globule transition of thermoresponsive polymers. Polymer–(co)solvent attractive interactions reinforce or compensate this mechanism and it is this interplay which drives polymer swelling or collapse

Oxygen gas and water vapor permeability of biaxially stretched poly(ethylene terephthalate)/poly(ethylene-co-vinyl alcohol) and poly(ethylene terephthalate-co-isophthalate)/poly(ethylene-co-vinyl alcohol) blend films

In this study, poly(ethylene terephthalate)(PET)/poly(ethylene-co-vinyl alcohol) (EVOH) and poly(ethylene terephthalate-co-isophthalate) (PETI)/EVOH (95/5 w/w) blends have been prepared with different types of compatibilizers using a co-rotating intermeshing twin screw extruder. Cast films have been stretched simultaneously and biaxially 2 and 3 times their original dimensions. Scanning electron microscopy, differential scanning calorimetry, oxygen gas and water vapor permeability analyzers have been employed for establishing the relationships among biaxial orientation, crystallinity, morphology, and chemistry on oxygen gas and water vapor permeability. The lowest oxygen gas and water vapor permeability values have been obtained when employed hydroxyl-terminated polybutadiene as the compatibilizer

Conformation and Aggregation of LKα14 Peptide in Bulk Water and at the Air/Water Interface

Historically, the protein folding problem has mainly been associated with understanding the relationship between amino acid sequence and structure. However, it is known that both the conformation of individual molecules and their aggregation strongly depend on the environmental conditions. Here, we study the aggregation behavior of the model peptide LKα14 (with amino acid sequence LKK­LLK­LLK­KLL­KL) in bulk water and at the air/water interface. We start by a quantitative analysis of the conformational space of a single LKα14 in bulk water. Next, in order to analyze the aggregation tendency of LKα14, by using the umbrella sampling technique we calculate the potential of mean force for pulling a single peptide from an n-molecule aggregate. In agreement with the experimental results, our calculations yield the optimal aggregate size as four. This equilibrium state is achieved by two opposing forces: Coulomb repulsion between the lysine side chains and the reduction of solvent accessible hydrophobic surface area upon aggregation. At the vacuum/water interface, however, even dimers of LKα14 become marginally stable, and any larger aggregate falls apart instantaneously. Our results indicate that even though the interface is highly influential in stabilizing the α-helix conformation for a single molecule, it significantly reduces the attraction between two LKα14 peptides, along with their aggregation tendency