Gloves and Condoms
While not high-technology medical applications, surgical/examination gloves and condoms represent about 10 million pounds of combined PU material volume. The two applications are about equal in size, and they are quite similar in technology. Additionally, both applications face varied competition from alternative polymer substitutes . PU gloves in particular have growth potential resulting from substitution of non-PU latex products due to allergy concerns and powder coatings interfering with sterile operations .
The production process for medical gloves and condoms is quite similar, differing primarily in film thickness (glove thickness is about 120-150 |jm, and condoms about 60|jm) . The greater thickness of gloves also necessitates a coagulation step using calcium nitrate as a precipitant. The precipitant acts by substituting Ca2+ ions from the coagulant for Na+ ions in the dispersion, which initiates precipitation . A simplified version of the dip procedure process for these materials is shown in Figure 11.10. A heated ceramic form or mold of the item is dipped into a bath of the PU dispersion. For thin films, a double dip is performed without coagulant. For a thicker film, a single dip is applied with the coagulant preapplied to the mold. The coated forms are then passed through a curing/annealing oven and then washed thoroughly of coagulants and migratory chemicals from the dispersion bath. There are many critical process parameters in this process including the cure step that has
FIGURE 11.10 Simplified process flow for making medical films such as examination/surgical gloves from aqueous polyurethane dispersion.
TABLE 11.3 Composition of a polyurethane prepolymer/curative that could be made into a dispersion using procedures outlined in chapter 10 to subsequently make medical gloves
Full formulations will often include surfactant and biocide additives to aid processing and film formation.
significant influence on the final tensile strength, and the cleanliness of the form/mold that can affect the development of pinholes in the films.
An example polymer composition of a glove-forming material and properties is presented in Table 11.3. The preparation of the dispersion made from the components in Table 11.3 would be similar to that diagrammed in Figure 10.11.