Type I & Type IV Circumallergenic Natural Rubber Latex Thin Films

Natural rubber latex from the Brazilian rubber tree, Hevea brasiliensis, is commonly used for thin film barrier applications in products such as condoms, medical gloves, and dental dams.  Type I and Type IV latex allergy sensitization and subsequent allergic reactions from Hevea natural rubber latex products have created an industry demand for thin film barriers that are circumallergenic (circumvent the allergic response).  Currently the circumallergenic thin film barrier market is populated with synthetic elastomers produced from non-sustainable resources such as petroleum.  These products often possess inferior mechanical properties. Both Heveaand synthetic thin film products are prone to causing Type IV contact dermatitis allergies, attributed to residual thiazoles, thiurams, and carbamates accelerators. 

We have developed circumallergenic natural rubber thin films, which circumvent both Type I and Type IV latex allergies, utilizing natural rubber latex from the plant species Parthenium argentatum, commonly referred to as guayule.  Guayule latex is circumallergenic to Type I allergy, because its proteins do not cross-react with Heveaassociated allergic proteins.  The guayule latex films were cured with the accelerators diisopropyl xanthogen polysulphide (DIXP) and alkyldithiocarbamate (ZDNC) (Robinson Brothers Ltd., West Bromwich, UK).  DIXP is consumed during the vulcanization process, and skin tests have shown that ZDNC does not cause dermal reactions or delayed contact hypersensitivity, thus eliminating Type IV allergy sensitization.  In addition, DIXP contains no nitrogen, phosphorous and metallic elements, and so is unable to form the volatile and carcinogenic N-nitrosamine compounds during vulcanization, reducing occupational hazards for latex industry workers.  

 Guayule natural rubber latex thin films have mechanical properties superior to those reported for Hevea natural rubber latex and synthetic elastomers.  For example, a 0.15 mm film had a tensile strength of 35.95 MPa, an elongation to break of 2080%, and a modulus at 500% of 1.58 MPa.  The thickest film to date is 0.26 mm and has a tensile strength of 43.49 MPa, an elongation to break of 2827%, and a modulus at 500% of 1.45 MPa.  The aforementioned thin films are well above the ASTM standards for surgical gloves, which state that natural rubber latex surgical gloves must possess max elongations above 750% and tensile strengths above 24 MPa, a modulus at 500% below 5.5 MPa, with a minimum thickness of 0.1 mm.  These materials are suitable for many dipped thin film product applications.