Technology

POLYMERIC PRESSURE SENSITIVE ADHESIVES FOR MEDICAL APPLICATIONS

-By Mr. P A Mahanwar & Ms. Farhana Yasmeen, University Department of Chemical Technology, Matunga, Mumbai 

VARIOUS PSAs USED FOR MEDICAL APPLICATIONS

a). Natural rubber :

The beginning of the pressure sensitive adhesive industry can be traced to the use of natural rubber in adhesive formulations.  In 1899, Johnson introduced a zinc oxide containing adhesive mass into their hospital tapes.  Early pressure sensitive tapes did not age well since the tackifying rosin was easily oxidized, thus causing the tapes to lose tackiness.  

In 1934, the Hercules Powder Company started manufacturing hydrogenated rosins, which substantially increased the adhesive aging resistance.

A shortage of natural rubber during World during World War II forced the evaluation of other polymers for pressure sensitive adhesive applications1.  

b) Styrene/Butadiene latexes-based adhesives :

Styrene/Butadiene (S/B) latexes are relatively new comers to the pressure sensitive adhesive industry.  They have been used for years as binders and adhesives for pigmented coatings.  These latexes are now replacing solvent borne rubbers in some pressure sensitive applications because concern over solvent emissions.

S/B latex is a colloidal dispersion of spherical polumer particles in water.  S/B latex is the product of the emulsion polymerization of styrene and butadiene.

Table 1 describes a simple recipe for the production of this latex.

c) Poly isobutylene (PIB) type pressure sensitive adhesives :

Polyisobutylenes (PIB) are a group of inherently tackly polymers that are widely used as pressure sensitive adhesives and as tackifiers and modifiers2.  They are homopolymers of isobutylene, polymerized using a Lewis acid type of catalyst, such as aluminium chloride.

Polyisobutylene have been produced over a wide range of molecular weights.  Unlike many other pressure sensitive adhesives, polyisobutylene adhesives are relatively formulated in house by device manufacturer or formulator, not by the polymer producer.  Although a wide range of properties can be obtained by varying the composition using the polymers of differing molecular weights, the addition of tackifiers, plasticizers, fillers, and stabilizers can also extend this range.

The low molecular weight polyisobutylene can be handled like any other viscous, tacky material.  They blend readily with oils, waxes, solvents and other polymers.  High molecular weight grades of polyisonutylene are normally shredded before formulation.  Preparation of a concentrqated solutionof the polymer and the adhesives is advisable prior to solvation.  Polyisonutylene are generally soluble in non-popular hydrocarbon and insolunle inpolar solvents.  Other additives can also be added such as plasticizers, fillers and antioxidants.  A representative formulation for a surgical tape is shown below.  It should be recognized that any additive to the basic polyisobutylene must also fulfilled biocompatibility requirements for the final adhesive system.'

Polyisobutylene adhesives formylation for surgical tape are presented in Table 2

| Page 1 | Page 2 | Page 3 | Page 4 | Page 5 | Back | Back To Top