Polyethylene Vinyl Acetate Copolymer Research Articles

Application of carboxylated ethylene/vinyl acetate copolymer-modified nanosilica in tire tread rubber

It is essential to keep the balance among rolling resistance, wet skid resistance and wear resistance (the so-called devil's triangle) of tire treads so as to ensure the reliability and safety of the vehicles. For this purpose, hexamethyl-disiloxane (HMDS) and carboxylated polyethylene vinyl acetate copolymer (EVA, emulsion polymer latex) were used to modify nanosilica by in situ surface-modification method, thereby obtaining surface-capped nanosilica possessing good compatibility and strong interfacial interactions with rubber matrix. The surface-capped nanosilica of the above both modifications were introduced into the blend of solution polymerized styrene butadiene rubber (SSBR) and butadiene rubber (BR), and its effect on the mechanical properties and wear resistance of the SSBR/BR-matrix nanocomposites was investigated. The results indicated that both HMDS and EVA contribute to enhancing the compatibility and interfacial interactions of nanosilica with the rubber matrix, which is favorable for improving the mechanical properties and wear resistance of SSBR/BR-matrix nanocomposites. Particularly, HMDS can endow the rubber-matrix nanocomposites with increased wet skid resistance, and EVA can ensure the low rolling resistance of the nanocomposites. Therefore, the SSBR/BR blend filled with HMDS–SiO2–EVA possesses the desired mechanical properties and wear resistance and shows promising prospective as a candidate material for fabricating high-performance tire tread.

MOISTURE ABSORPTION BEHAVIOR OF MALEIC ANHYDRIDE GRAFTED POLYETHYLENE MODIFIED ETHYLENE VINYL ACETATE COPOLYMER / HIGH DENSITY POLYETHYLENE NANOCOMPOSITES

The compatibilized poly ethylene vinyl acetate copolymer (EVA)/high density polyethylene (HDPE) /organomodified montmorillonite (OMMT) blend nanocomposites were prepared in a co-rotating twin-screw extruder followed by injection molding. Montmorillonite clay was modified by octadecylamine and aminopropyltriethoxysilane to make it organophilic. Maleic anhydride grafted high-density polyethylene was used as a Compatibilizer. Nanoclay was added in different proportions to the selected EVA/HDPE blend composition. The concentration of nanoclay was varied from1 to 5 phr in the polymer blend. The resulting nanocomposites were evaluated in terms of their water absorption behavior. Moisture absorption behavior of compatibilized blends is lower than their corresponding blend. On adding the nanoclay the moisture absorption behavior of blend nanocomposites changed at 4 phr nanoclay loading.

Investigating the feasibility of temperature-controlled accelerated drug release testing for an intravaginal ring

The objective of the present study was to investigate if temperature can be utilized to accelerate drug release from Nuvaring®, a reservoir type intravaginal ring based on polyethylene vinyl acetate copolymer that releases a constant dose of contraceptive steroids over a duration of 3weeks. The reciprocating holder apparatus (USP 7) was utilized to determine real-time and accelerated etonogestrel release from ring segments. It was demonstrated that drug release increased with increasing temperature which can be attributed to enhanced drug diffusion. An Arrhenius relationship of the zero-order release constants was established, indicating that temperature is a valid parameter to accelerate drug release from this dosage form and that the release mechanism is maintained under these accelerated test conditions. Accelerated release tests are particularly useful for routine quality control to assist during batch release of extended release formulations that typically release the active over several weeks, months or even years, since they can increase the product shelf life. The accelerated method should therefore be able to discriminate between formulations with different release characteristics that can result from normal manufacturing variance. In the case of Nuvaring®, it is well known that the process parameters during the extrusion process strongly influence the polymeric structure. These changes in the polymeric structure can affect the permeability which, in turn, is reflected in the release properties. Results from this study indicate that changes in the polymeric structure can lead to a different temperature dependence of the release rate, and as a consequence, the accelerated method can become less sensitive to detect changes in the release properties. When the accelerated method is utilized during batch release, it is therefore important to take this possible restriction into account and to evaluate the accelerated method with samples from non-conforming batches that are explicitly “out of specification” under real-time test conditions.

Effect of Solvent on Rheological Behavior of Iranian Waxy Crude Oil

Flow improvers are used extensively to increase the mobility of crude oil. This article deals with the relation between the rheological properties and solubility parameter of flow improvers in different solvents. Two types of Iranian waxy crude oils with different pour points were selected. The rheological behavior of this crude oil in the presence and absence of flow improvers in different solvents was measured. The rheological data cover the temperature range of 5°C to 40°C. Results show that the shear rate has an appreciable effect in decreasing viscosity, particularly at temperatures below the pour point. Poly ethylene-vinyl acetate copolymer (EVA) as flow improver with different range of molecular weights was used for the treatment of waxy crude oil. The results indicated that the performance of flow improvers was dependent on the molecular weight, type of solvent, and the type of crude oil. The phase behavior of EVA copolymers was investigated in various solvents. The flow improver in the poor solvent (cyclohexane) gave better results in improving the flowability of the crude oil, compared with the other solvent.

Effect of high-pressure processing on the mechanical and barrier properties of selected packagings

This investigation focuses on the effect of high-pressure processing (HPP) on possible changes of the mechanical properties and of the water vapour permeability of seven selected packaging materials. NOD 259 (PA-PE), BB4L (Cryovac-Grace packaging), PET/BOA/PE, PET/PVDC/PE, PA/SY, LDPE and EVA/PE were investigated (PET, polyester; PE, polyethylene; SY, surlyn; LDPE, low-density polyethylene; EVA, polyethylene–vinyl acetate co-polymer; BOA, biaxially oriented polyamide). These packaging materials were selected because of their interest to the food industry. All had an internal film of PE for food use. High-pressure tests were realized at 10°C for 10 min at pressures of 200, 400 and 600 MPa, with water as a food-simulating fluid. The depressurization rate was either rapid (pressure drop in <10s) or slow (20 MPa/min). Permeability to water vapour was realized using the NFF H 00 030–ASTM E96-90 standard. Mechanical tests were carried out with a tensile testing machine (Lloyd LR5K), according to the NF 54-102 standard. Maximal stress, rupture stress and strain at rupture were evaluated with non-treated and treated samples. Obtained results showed that HPP minimally affects the mechanical strength of packaging material. The depressurization rate did not have any significant influence in our conditions. The barrier properties to water vapour were not significantly affected and were even slightly enhanced for LDPE, which is a packaging material commonly used for HPP applications and at least as a food contact material. Copyright © 2006 John Wiley & Sons, Ltd.

In vitro release properties of etonogestrel and ethinyl estradiol from a contraceptive vaginal ring

The release properties of steroids from a combined contraceptive vaginal ring have been investigated. The product design is based on a coaxial fiber consisting of two types of polyethylene vinylacetate copolymers. Inside the core of the fiber, two steroids are present in a molecularly dissolved state. In order to design a controlled release system with specified release characteristics, values of diffusion coefficient and solubility are required. These data can either be determined during pre-formulation studies on e.g. polymeric flat films or from in-vitro release measurements of the actual coaxial fibers. It can be concluded from this study that polyethylene vinylacetate copolymers exhibit suitable properties to develop a controlled release system with the two steroids etonogestrel and ethinyl estradiol. It has been found that the permeability data obtained in the pre-formulation studies are useful in semi-quantitative terms, but deviate from the permeability data found from the in-vitro release of coaxial fibers. This is most likely due to differences in the polymeric structure of films and coaxial fibers. As a consequence, further studies should be initiated to evaluate the relationship between the manufacturing process and the resulting polymeric structure. It has also been found that the solubility and release of etonogestrel are influenced by the concentration of ethinyl estradiol. By investigating this phenomenon by thermoanalysis, it was shown that the steroids form an eutectic. The lower melting point of the steroids results in an increase in solubility and hence in altered permeability properties.

Pharmacokinetics of 7α-methyl-19-nortestosterone (MENT™) delivery using subdermal implants in healthy men

We studied the pharmacokinetics of 7α-methyl-19-nortestosterone (MENT), a potent synthetic androgen, administered by subdermal implants. The implants contained 112 ± 4 mg of MENT acetate in a polyethylene vinyl acetate copolymer. MENT acetate released from the implants is rapidly hydrolyzed to MENT in vivo. Fifteen healthy Finnish men were randomized to have either one, two, or four implants inserted in the medial aspect of the upper arm. The implants remained in place for 4 weeks. Blood samples were obtained before implant insertion, 1, 2, 3, and 4 weeks after insertion, and 1 and 2 weeks after removal. Serum MENT concentrations were determined by gas chromatography with mass selective detection. The MENT levels attained in each implant group remained at a steady level during the 4 weeks of implant use. The mean steady state MENT concentrations in the one, two, and four implant groups were 0.6, 1.4, and 2.3 nmol/L, respectively. Serum MENT concentrations during implant use were clearly dose dependent; the between-subject effect of implants as well as the differences between each pair of groups were all statistically significant. The release rate of MENT from one, two, and four implants was calculated to be approximately 0.3, 0.8, and 1.3 mg/day, respectively. This study suggests that MENT acetate implants are a promising method for long-term androgen administration in hypogonadism and male contraception.