UV-Absorbing Gallic Acid Derivatives as Functional Reinforcing Fillers in Poly ( Vinyl Chloride ) Films

The poly(vinyl chloride) PVC was photostabilized by gallic acid derivatives (0.5% by weight). The photodecomposition rate constant was reduced significantly in the existence of gallic acid derivatives along withPVC (blank). R1 compound was found to be the most effective stabilizer in photostabilization of PVC. The photodecomposition rate constant for PVC films containing R1 was found to be 1×10-4 compared to 8×10-4 sec-1 for PVC films in the absence of any additives. Different mechanisms of photostability for PVC films that involvegallic acid derivatives have been proposed. Article history Received:19 October 2017 Accepted: 5 january 2018


introduction
Plastics have played an indispensaable role in ourlife and production as the most significant material of the 21 st century.Plastics are closely utilized in different parts of civil life, manufacturing, and aerospace technology because of their excellent material features, including cheap,strength and lightweight 1 .There are 10,000 companies in the United State alone that are interested in manufacturing, processing and fabricating polymeric materials 2,3 .
Polymers are classified into natural and artificial types.Polystyrene, Polyester and poly(vinylchloride) are examples of synthetic polymers 4,5 .Poly(vinyl chloride) is the most extensively employed thermoplastic materials worldwide, with more than 31 million tons produced per annum [6][7][8][9] .PVC the second most widely consumed plastic, is a 21st century material 10,11 , mostly utilized inseveral industrial applications such as toys, tubes, food packaging, medical devices, building applications, electronics and furnishings 12- 14 .Photodegradation occur as a result of chemical reaction, or photochemical degradation, which could be startedby the UV solar radiationenergy 15 .However, long term exposure of PVC to sunlight and/ or high temperature lead to its photo degradation 16 .Neat PVC is usually mixed with other additives to get a plastic with desired properties depending on theintended industrial use 17 .
Photostabilization of PVC can be established through the use of various additives.The additionjust a little content by weight of additivesprogress polymer properties, occasionally, it dueto a unique combination of properties 18,19 .The most common additives are Schiff base complexes 20 , heterocycles 21 , plasticizers 22 , metal complexes and inorganic salts 23 , aromatics 24,32 .In the present study,we investigated the (k d ) photodecomposition rateconstant of PVC polymeric filmsincluding gallic acid derivatives on irradiation with UV light.

experimental Materials
From Sigma-Aldrich (Gillingham, UK) all reagents and solvents were purchased and have been utilized without further purification.K value and polymerization degree of PVC= 67, 800 respectively, it was purchased from Petkim Petrokimya(Istanbul, Turkey).

Preparation of materials
Homestead, FL, USA) were utilizing to fix PVC films 26 .40 µm Thickness of PVC films was measured by a DigitalCaliper Vernier (Kevelaer, Germany).
Photodecomposition Rate (k d ) of PVCFilms using UV spectrophotometer 28 A Shimadzu UV-Vis 160A-Ultraviolet Spectro photometer (Shimadzu Cooperation, Kyoto, Japan) was utilized to measure changes in the UV-visible spectra of PVC films during irradiation (λ max =313 nm).k d of PVC films were calculated using Equation (1).
Where, a =A 0 -A ∞ , x = A 0 -A t , a = PVC concentration at t = 0 and x = change in concentration of PVC at time t during irradiation as seen in Equation ( 2), A o = the absorption intensity of the PVC at t o , A ∞ = the absorption intensity at t ∞ and A t = the absorption intensity after irradiation time t.
The plot of ln(A t -A ∞ ) against time of irradiation(t) gives straight line in which the slope=k d .The PVC photodecomposition follows a first order kinetics.

Films Preparation
C o m m e r c i a l P V C wa s r e -p r e c i p i t a t e d i n tetrahydrofuran (5 g/100 mL) with ethanol and dried for 24 h at 20˚C under reduced pressure.The gallic acid derivatives (0.5% byweight) were mixed with PVC at 20˚C based on literature procedure 25 then aluminum plate stands(Q-Panel Company,

Results and Discussion
The effect of gallic acid derivatives (R 1 , R 2 , R 3 , R 4 ) on the PVC films photodecomposition was investigated.
The PVC films (40 µm thickness) containing gallic acid derivatives (0.5% by weight)were irradiated with a UV light (λ max = 313 nm) for 250 h.PVC films in the absence any additives.Figures 3-6 show the changes in the ln (A t -A ∞ )against time of irradiation of PVC films including gallic acid derivatives (0.5% by weight) as stabilizers for PVC films on irradiation with light.
The first order photodecomposition rateconstant (k d ) for PVC films containing gallic acid derivatives (0.5 wt %) along with that for PVC (blank) is shown in Table (1).Table (1) and Figures (2-6) show that the rate constant (k d ) values are sensitive to thepresence of gallic acid derivatives and itssubstitution.The PVC photodecomposition rateconstant was high (8× 10 -4 sec -1 ) in the absence of any additives.Such rate constant has been reduced significantly (1-5 × 10 -4 sec -1 ) when gallic acid derivatives were used as additives.The photostabilization of PVC in the presence of gallic acid derivatives follow this order R 1 < R 2 < R 3 < R 4 .The R 1 was the most efficient than the other derivatives in photostabilization of PVC films.Clearly, these derivatives have acted as photostabilizers for the photostabilization of PVC films.The photodecomposition rate constant was highest for PVC (blank) and lowest in the presence of R1derivative.Such photostabilizers could play as HCl scavengers, primary stabilizers, peroxide decomposers, radical scavengers and UV absorbers 29 .

Propose Mechanisms of PVC Photostabilization
The efficiency of additives as PVC photostabilizers was measured as a function of the changes in the photodecomposition rate constant value.The values were smaller in PVC films containing gallic acid derivatives along with PVC itself.Different mechanisms of photostabilization process of PVC films containing gallic acid derivatives can be proposed schemes 1 and 2.
Two different atoms and different electro-negativity (nitrogen and sulfur) in the 1,3,4-thiadiazole ring.The thiadiazole ring polarity demonstrates the attraction between the PVC chains and stabilizer as shown in scheme 1.This mechanism can due to that the crosslinking could occurby UV irradiation, which may be correct for all compounds 30 .
The heteroaromatic and aromatic rings can play as UV absorbers 31 .These systems have electron rich within stabilizer backbone structures can absorb the UV radiation energy directly and dissipates it to harmless heat energy, scheme 2.
The UV irradiation due to a clear changein PVC films and decomposition took place.ln (A t -A ∞ )plot against time of irradiation (t) gave a straight line.The graphs showed first order kinetics in which the slope equaled k d constant for PVC films.Fig.2demonstrates the change in ln(A t -A ∞ ) against time of irradiation(t) of