ACID RAIN DEGRADATION OF NYLON (POLYAMIDE, PHOTODEGRADATION)

KAREN E KYLLO, Purdue University

Abstract

Acid rain, precipitation with a ph less than 5.6, is known to damage lakes, vegetation and buildings. Degradation of outdoor textiles by acid rain is strongly suspected but not well documented. This study reports the effects of sunlight, aqueous acid, heat and humidity (acid rain conditions) on spun delustered nylon 6,6 fabric. Untreated nylon and nylon treated with sulfuric acid of ph 2.0, 3.0 and 4.4 were exposed to light in an Atlas Xenon-arc fadeometer at 63(DEGREES)C and 65% R.H. for up to 640 AATCC Fading Units. The untreated and acid treated nylon fabrics were also exposed to similar temperature and humidity condition without light. Nylon degradation was determined by changes in breaking strength, elongation, molecular weight, color, amino end group concentration NH(,2) and ('13)C NMR spectra. Physical damage was assessed using SEM. Nylon exposed to light without acid exhibited breaking strength, elongation and molecular weight losses. The increase in NH(,2) and decrease in peak intensities in the ('13)C spectra indicated chain scission at bonds other than the amide linkage. Pits and cavities indicated by SEM were characteristic of light induced degradation. The addition of H(,2)SO(,4) to the light exposure did not increase degradation of the nylon until 160 FU exposure at ph 3.0 and below. As acid strength and exposure level increased, synergism between light and acid produced even greater losses in breaking strength and molecular weight. Higher NH(,2) and increased intensity of the carbonyl carbon peak in the ('13)C spectra indicated that acid hydrolysis produced chain scission predominantly at the amide linkage. Deep elongated cavities and a roughened surface were observed in SEM photographs of these fibers. Dark exposure with acid, heat and humidity also produced chain scission. As acid strength increased, chain scission increased. SEM and decreases in ('13)C peak intensities indicated that the degradation was similar to that produced by light exposure. Increases in NH(,2) following 320 FU dark exposure with ph 2.0 acid indicated that some acid hydrolysis also occurred. Yellowing of the nylon was found to correlate with chain scission initiated by light exposure. Results of this study indicate both physical and chemical damage of nylon by acid rain, particularly in areas of intense sunlight and highly acidic precipitation.

Degree

Ph.D.

Subject Area

Polymers

COinS