|
Evaluation of Plasticisers for PVC for Medical Devices 8 ConclusionThe investigations conducted in this project confirm that an extensive effort is needed before one can decide to substitute di(2-ethylhexyl) phthalate (DEHP) with any other plasticiser. It is a well-known fact that DEHP is by far the most investigated PVC plasticiser substance. In the plasticiser performance matrix created in this project DEHP is the only substance, of which no information is lacking. No matter which alternative to DEHP one might want to use, a substantial new knowledge must be generated. Based on this project, i.e. within the limitations of the investigated properties, it seems likely, that diisononyl phthalate (DINP), di(2-ethylhexyl) adipate (DEHA) and acetyltributyl citrate (ATBC) can give PVC compounds with properties that are comparable to those of DEHP plasticised PVC. The only drawback (apart from the cost) with the investigated polyadipate seems to be the poorer cold flexibility of the compound. The cold flexibility temperature is some 10°C higher than that of the DEHP plasticised compound. The values found are -10°C for the polyadipate and -20°C for DEHP. Even though the compatibility towards PVC has been reported to be limited, no drawback was found in this investigation that can be explained by this. Triethylhexyl trimellitate (TEHTM) also looks interesting, if a decrease in the tensile strain at break can be accepted for the application in question. Di(2-ethylhexyl) sebacate (DEHS) gives compounds with a substantially lower tensile strength, and the tensile strain at break is also lower at least in film thickness, but depending on the specific application it might also be an interesting replacement for DEHP. The investigated benzoate (dipropylene glycol dibenzoate) results in a compound with a cold flexibility that is worse than with the polyadipate; the cold flexibility temperature value found is -3°C. Furthermore, the tensile strain at break is substantially decreased - nearly 30 % tested at a crosshead speed of 200 mm/min. The most important disadvantage (apart from the cost) of the investigated ethylene-acrylate-carbon monoxide terpolymer (EAC terpolymer) is the very poor cold flexibility of the compound. The cold flexibility temperature was found to be as high as +11°C. The tensile strength of PVC compounds plasticised with this substance is some 35 % higher than that of compounds plasticised with DEHP. The tensile strain at break, however, is reduced to 44 % determined at a crosshead speed of 100 mm/min and to 80 % determined at 200 mm/min. Presumably, the potential for use for Medical applications is limited due to these limited properties. To replace plasticised PVC with another plastics material is highly depending on the actual final product and its application. In this project an ethylene-vinyl acetate copolymer has been considered. It is worth to note that EVAC is known to emit acetic acid during processing like extrusion or injection moulding. The final evaluation can only be made after assessment of biological properties and further investigation of Medical articles like tubings, catheters and bags made of the relevant compounds. However, this is not included in this project but is expected to be made in a subsequent project.
|