Ethylene vinyl acetate copolymer development

Nondegradable polymers are also useful as matrices for ocular implants. This application requires the polymer to be hydrophilic, to minimize local tissue irritation. Need for ocular implants stems from the challenges posed to conventional ocular medicines (i.e., eye drops) such as rapid dilution, tear washout, poor patient compliance, and limited bioavailability. Ocular implants from hydrophilic polymer matrices that provide localized sustained release may overcome the above limitations. The first polymeric sustained release product to reach the market was Ocusert , a pilocarpin sustained release ocular implant developed by Alza. Ocusert has the drug reservoir as a thin disc of pilocarpine-alginate complex sandwiched between two transparent discs of microporous membrane fabricated from ethylene-vinyl acetate copolymer. The microporous membranes permit the tear fluid to penetrate into the drug reservoir compartment to dissolve pilocarpine from the complex. Pilocarpine molecules are then released at a constant rate of 20 or 40 pg/hr for a four- to seven-day management of glaucoma. 

A new approach was proposed for making effective helmets which could replace the former British army steel helmet. Essentially the new helmet used modified phenolic resins reinforced with nylon, and the crown cap inside was thermoformed from polyethylene. Formerly the crown cap was attached to the steel by rivets—not an appropriate method for fixing polyethylene to reinforced plastics. Instead a method was developed with a hot-melt adhesive based on ethylene-vinyl acetate copolymers cast as film on release paper. For assembly, the cast film is cut in advance to match the intricate shape required and activated by heat to bond under light pressure subsequently, a further heat activation is employed to fix the crown cap in place (Figure 52 illustrates this). 

As reported by Diehl et al. [58], interpolymers are also compatible with a broader range of polymers, including styrene block copolymers [59], poly(vinyl chloride) (PVC)-based polymers [60], poly(phenylene ethers) [61] and olefinic polymers such as ethylene-acrylic acid copolymer, ethylene-vinyl acetate copolymer and chlorinated polyethylene. Owing to their unique molecular structure, specific ESI have been demonstrated as effective blend compatibilizers for polystyrene-polyethylene blends [62,63]. The development of the miscibility/ compatibility behavior of ESI-ESI blends differing in styrene content will be highlighted below. 

Not all solvent adhesives will he replaced with latexes per se. For some applications, hot melt adhesive systems are heing developed. However, just as ethylene-vinyl acetate copolymers produced by emulsion polymerization are a major component of many hot melt systems, suitably designed emulsion polymers to meet specific requirements will probably he present in these systems, too. 

Ethylene vinyl acetate copolymers are used as membranes and backings in laminated transdermal drug delivery systems. They can also be incorporated as components in backings in transdermal systems. Ethylene vinyl acetate copolymers have been shown to be an effective matrix and membrane for the controlled delivery of atenolol triprolidine, and furose-mide. The system for the controlled release of atenolol can be further developed using ethylene vinyl acetate copolymers and plasticizers. ... 

Plastics wastes used as aggregate of the mortar are expanded polystyrene (PS) and expanded ethylene-vinyl acetate copolymer (EVAc). Expanded PS is obtained from packing materials wastes and so on. Now, about 9,200 tons of expanded PS have been crushed and used as lightweight aggregate for plastering materials every year in Japan. EVAc chip is found in cushion materials for shoes etc. These plastics wastes are crushed and graded for the purpose. This mortar was developed about 20 years ago. The suitable application of this mortar has been discussed and studied until now. 

Early pressure-sensitive hot-melt adhesives used ethylene-vinyl acetate copolymers as elastomers, but they are seldom used now. Atactic polypropylene is sometimes used on its own or in admixtures. More recently, vinyl ethers and acrylic resins have become available and will probably play an increasingly important role as the technology is developed, especially on polar surfaces. 

Since the 1940s continuous polymerization processes have been developed for a variety of products and with different reactor configurations. Latex products manufactured in continuous systems include polychloroprene and other synthetic elastomers, ethylene-vinyl acetate copolymers, components for engineering plastics and coating formulations. 

Chattopadhyay, S., Chaki, T. K., Bhowmick, A. K., Development of new thermoplastic elastomers from blends of polyethylene and ethylene-vinyl acetate copolymer by electron-beam technology. Journal of Applied Polymer Science 2001, 79, 1877-1889. 

One of the new developments in hot-melts is the application of foam technology. Several years ago, the Nordson Laboratory (84,85) discovered that the foamed hot-melts are easier to spread than the non-foamed hot-melts. Later, foamability (86) studies were carried out for the following hot-melt adhesives polyethylene, polypropylene, polyamide, ethylene-vinyl acetate copolymer, and polyester. Air, CO2, and nitrogen were used as the blowing... 

Ethylene-vinyl acetate copolymers, usually known as EVA, are used in many applications, but especially for low voltage cables. These polymers are easily flammable and flame retardants are added to reduce their flammability. The classic solution is to incorporate aluminium hydroxide or magnesium hydroxide that develop endothermic reactions when heated. Nevertheless, large amounts have to be incorporated, often around 60% and this can lead to a loss of mechanical properties in the compound. Intumescent technology that works well with polypropylene has also been tried for EVA polymer systems. 

The next two decades saw the development of new polymers such as thermoplastic PU (1961), aromatic polyamides, polyimides (1962) polyaminimides (1965), thermoplastic elastomers (styrene-butadiene block copolymers in 1965), ethylene-vinyl acetate copolymer, ionomers (1964), polysulfone (1965), phenoxy resins, polyphenylene oxide, thermoplastic elastomers based on copolyesters, poly butyl terephthalate (1971) and polyarylates (1974). 

Chlorinated rubber is used in topcoats for heavy duty maintenance paints because of its low water permeability. It is also used in tie coats on polyolefin plastics. Chlorinated rubber dehydrochlorinates and requires stabilizers similar to those used with PVC. Some metal salts, especially those of iron, tend to promote degradation of chlorinated rubber and so it degrades when applied over rusty steel. Chlorinated ethylene/vinyl acetate copolymers have been developed that can be used to replace chlorinated rubber in at least some applications (183). 

Currently magnesium hydroxide is predominantly used in polyethylene and ethylene vinyl acetate copolymers for electrical wire covering. The areas of greatest potential are, however, in PP and polyamides for a wide variety of uses, and it is in these areas where most development work is currently directed. 

Rubbers and elastomeric products for practical applications are usually blends of different elastomer types that develop specific domain morphologies at the microscale, and, therefore, they are a part of this chapter. The most common representatives of the ruhher family are natural ruhher (NR) and the synthetic polyhutadiene ruhher (PB). There are various copolymers of butadiene with styrene (styrene butadiene rubber, SBR) or acrylonitrile (acrylonitrile-butadiene rubber, NBR). Several elastomers have been developed for special purposes, such as EVA (ethylene vinyl acetate copolymer), PU (polyurethane), EPDM (ethylene propylene terpolymer), and siUcone rubber. 

The latter device, developed by Alza Corp., Palo Alto, California, is a diffusion unit consisting of a drug reservoir (e.g., pilocarpine HCl in an alginate gel) enclosed by two release-controlling membranes made of ethylene-vinyl acetate copolymer, and enclosed by a white ring which Slows positioning of the system in the eye. The Pilo-20 Ocular Therapeutic System has a release rate of 20 mg/hr for 7 days, and the Pilo-40 system a release rate of 40 mg/hr for 7 days. The former releases a total of 3.4 mg in 7 days, the latter 6.7 mg. In order to maintain constant release of tog, and in accordance with the principles of diffusion, there... 

Koopmans RJ, van der Linden R, Vansant EF (1980) The characterization of newly developed and promising hydrolyzed ethylene vinyl acetate copolymers. J Adhesion 11 191-202... 

G.W. GUby, In Developments in Rubber Technology, Vol. 3, Eds. A. Wheelan and K.S. Lee, Applied Science Publishers, New York, 1982, Chapter 4, Ethylene-Vinyl Acetate Copolymers, pp. 101 144. 

The use is examined of thermogravimetric analysis as an analytical tool for the diagnosis of part failure in injection moulding. The consistent performance of an ethylene vinyl acetate copolymer was evaluated and the need to separate the component parts of the material to test for the amount of vinyl acetate in the compound is discussed in order to develop a thermal history. Once this history is established, a customer can institute an incoming QC test on the material s composition rather than by adjusting the process for each new lot and performing product testing after the parts have been produced. 

Currently ethylene-acrylate and ethylene-vinyl acetate copolymers are commercially produced by radical polymerizations in high-pressure reactors. In recent times much effort has gone into developing singlesite catalysts for the copolymerization of ethylene and polar vinyl monomers. 

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