Hideharu Shintani

Analysis of the carcinogen 4,4′-methylenedianiline (MDA) in gamma-ray and in autoclave-sterilized polyurethane

SummaryA carcinogen, 4,4′-methylenedianiline (MDA, p,p′-diaminodiphenylmethane), was determined in gammaray- and in autoclave-sterilized thermoplastic polyurethane (PU). The determination of MDA in aqueous extracts of PU has been reported, however recovery of MDA and its determination using a complete dissolution of PU by organic solvents have not. In addition, we report the MDA determination in methanol extract of PU. No MDA was detected in gamma-ray sterilized thermoplastic PU, but in autoclavesterilized thermoplastic PU, MDA was detected (possibly formed by hydrolysis). The amount of MDA formed was inversely related to the molecular weight of PU by a second order equation. No change in the weight average molecular weight was observed as a result of autoclave sterilization. Essentially the same amounts of MDA were extracted from PU with serum as with methanol.

DEGRADATION AND CROSS-LINKING OF POLYURETHANE IRRADIATED BY GAMMA-RAYS

A study has been conducted to clarify the mechanism of cross-linking and degradation of thermoplastic polyurethane (PU) when it is irradiated with gamma-rays. Changes in molecular weight, UV absorption, and the amount of PUs with amino groups caused by irradiation were determined. Thermoplastic PU chain-extended with 1,4-butanediol (BU) showed degradation, while thermoplastic PU nonchain-extended with BU predominantly showed cross-linking as a result of gamma-ray irradiation. The amount of PUs with primary amino groups increased linearly with increasing irradiation levels and the amount was approximately 10 μ equivalents per gram of sample at the highest level. This amount corresponded to approximately 20% of the amount calculated, indicating that degradation occurred partly at 4,4′-diphenylmethane diisocyanate (MDI)-BU hard segments. The molecular weight of degraded PUs was approximately 12 to nearly 13 that of the original Mw. This Mw change was greater than that estimated from the amount of PU with primary amino groups produced, indicating that degradation occurred predominantly at polytetramethyleneglycol (PTMG) soft segments (about 80 to 90% of the whole degradation). Characteristic differences were seen in cross-linking between nonchain-extended thermoplastic PUs based on various molecular weights of PTMG (Mw of PTMG 640 to 2800). PUs fabricated from PTMG of greater molecular weight showed greater cross-linking. The cross-linking ratio is linearly proportional to the molecular weight of PTMG, indicating that cross-linking at PTMG soft segments was predominant (the ratio of cross-linking at PTMG was more than 90% of the total cross-linking). In gamma-ray irradiation both cross-linking and degradation occurred predominantly at PTMG soft segments.

Effects of gamma-ray irradiation on the change of characteristics of polyurethane

Abstract Investigations have been carried out on the characteristic changes which occur in thermoplastic polyurethane (PU) when it is irradiated by gamma rays. The change in molecular weight as a result of irradiation and the change of absorbance of samples eluted by methanol were determined. GPC patterns, tensile strength and residual amount of radicals based on chemiluminescence were also measured. PU chain-extended with 1,4-butanediol (BU) showed degradation, while nonchain-extended PU showed mainly cross-linking by gamma-ray irradiation. G values of degradation and cross-linking were 1·1 and 0·2, respectively. A linear relationship between the irradiation dose and the residual amount of radicals was found. There was no significant difference between molecular weights determined immediately following irradiation and 6 months after irradiation. The influence of the amount of residual radical on the changes in the characteristics of PU was not significant. The elution of PU oligomers ( n = 1–10) was confirmed from the GPC pattern of the methanol extract. Changes in tensile strength correlated well with changes in molecular weight. Sequential daily methanol extract analysis showed that elution occurred semilogarithmically. The GPC pattern suggested more rapid elution of lower molecular weight compounds which were more toxic.