Photostability Study of Some Modified Poly(vinyl chloride) Containing Pendant Schiff’s Bases

The polymers modified Poly(vinyl chloride) differ in their tendency to photo oxidation comparing with that unmodified. It has been studied Photostability for modified Poly(vinyl chloride) chains using Schiff’s bases derivative of (5-amino-1, 3, 4-thiadiazole-2-thiol) in a manner casting of plastic chips with thickness (40) in a solvent Tetrahydrofuran. It has been determined the effectiveness Photostability of these modified polymers through the photo degradation rate constant for photostabilizer (k d ) for the modified Poly (vinyl chloride). Attributed efficiency of these Poly(vinyl chloride) chips in Photostability by replace the atom Cl Poly(vinyl chloride) chains ends more stable than light stabilizer.


Introduction
Poly(vinyl chloride), better known by its abbreviation (PVC), is one of the most significant polymers due to its competent properties, the growth of the Polyvinyl chloride production is due to the stable expansion of its application fields [1].Poly(vinyl chloride) is known from poor thermal and light stability.It subject rapid autocatalytic dehydrochlorination upon exposure to heat and light [2,3].However, low photo stability of Poly(vinyl chloride) leads to hydrogen chloride loss, discoloration, and dangerous corrosion phenomena, accompanied by changes of physical and chemical properties of the Poly(vinyl chloride).The increased use of poly(vinyl chloride), a low-cost ratios and good performance, which make it more widely used in outdoor applications such as windows, doors cladding, and pipes [4].Using effective stabilizers is designed to prevent or slow down the process of deterioration earn Poly(vinyl chloride) protection against thermal and photodegradation in order to extend their use in (outdoor) applications through their resistance photodegradation over long periods of exposure to the sun [5] .
Scientists have used Schiff's bases compounds as Photostabilizers of poly(vinyl chloride) polymer against photodegradation by ultraviolate radiation [6].
The interaction admixture was then allowed to cool to room temperature and filtered.The filtrate was vaporized under vacuum then (50 ml) (cold distilled water)was added, acidification with HCl drop(conc.)by drop was executed whiteyellowish, precipitate was formed, the precipitate was composed by filtration, and distilled water with washed , re-crystallized using hot distilled water.

Accelerated tested technique
The samples were placed in Accelerated weathering tester (Q.U.V) it used for the irradiation of polymeric chips.The sources Uv-Visible giving range (250-380) nm and the light intensity is 6.2×10 -9 ein dm −3 sec -1 .The polymer chips samples were fixed vertically and parallel to the lamps to be sure that light incident radiation is vertically incident on the samples, the irradiation samples are changed places from time to time to be sure that the ntensity of light incident on all samples is equal.The distance between the polymer chips and light source was 10 cm [9].

Measuring the Photodegradation Rate of Polymer Chips
By useing the UV/Vis Spectrophotometers (Perkinelmer LAMBDA 25) to measure the change in the UV -visible spectrum during the irradiation time for each polymer chips at the maximum absorption band.The absorption spectrum was measured in the range of ( max = 200-400) nm .The photodegradation rate constant for photostabilizer )k d ( calculated using the first order kinetic equation, ln(a-x) = ln a -k d t ......... (1) Where: a : represents the stabilizer concentration before irradiation.
x : represents the change in stabilizer concentration after irradiation time (t) .If (A O ) represents the absorbance of the film Poly(vinyl chloride) containing a certain concentration of compound added before irradiation .process (At) absorbance after the passage of time (t) on the irradiation process.And (A∞) represents the absorbance at infinity, than: a = Ao-A x = Ao-At a -x= Ao-A -Ao + At= At -A....(2) substitution of (2) in (1) from equation gives: ln(At -A) = ln (Ao -A) -k d t.... (3) Thus a plot of In (A t -A ∞ ) exchange for irradiation time (t) in seconds produces a straight line is a tendency (K d ) and this shows that photodecomposition of additives are first order [10].

Results and Discussion:
Uv radiations are known to have deleterious effects on most polymers inducing chemical modification and cleavage of polymer chain, which ultimately lead to an unwanted loss of the mechanical and surface properties of the irradiated material.The prepared Schiff's bases were used as photostabilizers to modified Poly (vinyl chloride) films comparing with unmodified PVC chips [11].The added substances used to be totally soluble in Tetrahydrofuran solvent.It has been be noticed that the added substances used in this work are photodecomposed during the photolysis.Thus the photodecomposition rate constant (k d ) was calculated .The (k d ) values were computed using the UV spectra changes of poly(vinyl chloride) chips thickness (40 m) containing groups of Schiff's bases.The photolysis.Along these lines the photodecomposition rate steady (k d ) was calculate The ( k d ) qualities were registered utilizing the UV spectra changes of [12] The plot of illumination time versus ln(At-A∞) gives straight line which indicates primarily the first order reaction.The slope equal to the decomposition rate constant k d .Fig. (1) demonstrates the variety of ln(At -A ∞) with irradiation time for all added substances in poly(vinyl chloride) chips at the wavelength 365nm.

2 -
Scheme 1 :Preparation of 5-amino-1, 3, 4-Thiadiazole-2-Thiol Synthesis of Schiff's Bases of 5-amino-1,3, 4-Thiadiazole-2-Thiol Compound.Schiff's bases is prepared from melting different aldehyde in absolute ethanol in a glass beaker circular capacity (200 ml) and added of (5-amino-1, 3, 4thiadiazole-2-thiol) dissolved in 20 ml of absolute ethanol and two drops of acetic acid glacial.The interaction by paying (1: 1) of the Secretary-record and aldehyde in respectively, climbing mix (Reflux) with stirring a period of time ranging from two and a half to four hours consists precipitation is sucked off and wash the amount of alcohol (85%) and are re-crystallization by a mixture of ethanol and methanol (20:80) respectively .