Decarboxylation Kevlar

The photodegradation of para-aramid in an 0 atmosphere allows the differentiation between the accelerated experimental photooxidative conditions from its usual daylight exposure effects. This study illustrated an estimation of the rates of photooxidation of a commercial para-aramid product (i.e., DuPont s Kevlar-29 woven fabric) based on the oxygen-18-labelled carbon dioxide ( CC and CC ) decarboxylated from the sample. The oxygen-18-labelled atoms, which are inserted in the macromolecules, were analyzed for the photodegradation processes. This technique also allows the radial l O-distribution measurement from the fiber surface toward the fiber center. 

The total carbon available for decarboxylation from 0.415 g Kevlar fabric sample [expressed as C.H.N0-4- mojeties in moles, i.e., 3.49 x... 

There are consistently two types of decarboxylation reactions that occur at 196 C (R1 and R2) of a given Kevlar sample [expressed as -f-Cyti-NO-l— moieties in moles], whether it was exposed or not exposed to photolysis one yields one mole of CO. per —f—C-.H.NO-4- moiety and the other gives... 

Some of the possible photooxidized sites of the Kevlar macromolecules before decarboxylation are illustrated below (Equations 1 and 2) ... 

Figures 2 and 3 illustrate the pseudo first order decarboxylation reactions of C02 (the slow reaction with ty. = 42 hr) and C02 (the fast reaction with tt = 8 min). The photodegraded sample was exposed for 7 minutes at I00°C in 0.2 atm 02. The concentration of - -80-Kevlar is expressed as -fCyH NO)- in moles and is equal to the total C02 minus evolved C02 in moles for Figure 2 and the total 48co2 minus evolved C02 in moles for Figure 3.

Tableir.Surmary Data on Decarboxylation of Kevlar and its Ra of Oxygen (as a Constituent in 44c02 °C°2 anli °C°2)...

Table III lists the photooxidation rates, which were deduced from four pseudo first order decarboxylations of C02 at 196° and 25°C and 8co2 at 196° and 25°C. The initial concentrations of fC7H5NO)-n to produce % - - 02 (i.e., to produce C02 product) is 6.1 mole l-- - and to produce l o2 (i.e., to produce 48cq2 product) is 12.2 mole l- using the density of Kevlar at 1.45 g/cm (2). The - 02 is assumed as an ideal gas at 100°C and 0.2 atm. The 0.415 g Kevlar-29 fabric expressed as C7H5NO moieties in moles is 3.49 x 10"3 moles.

This new and novel method to study the photochemical degradation of Kevlar-29 fabric in air divides into four steps (1) fabric cleaning, (2) photolysis at specified temperature and time in 0.2 atm - 02, (3) preparation of the degraded (DMAc-soluble) sample surface for decarboxylation at 25° and 196°C in the concentrated sulfuric acid, and (4) the total carbon dioxide analyses by gas chromatography and the isotopic carbon dioxide ( °C02 and 48co2) ratios by GC-mass spectrometer. 

Data are deduced from pseudo first order decarboxylations at 196°C for 20 m1n from the top surface layer of the photolyzed Kevlar ... 

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