Diamine Derivatives as Photostabilizers for Thermoplasticized Poly(Vinyl Chloride) [I]

The photostabilization، of poly vinyl chloride (PVC) ، films has been investigated by using diamine derivatives. The، (PVC) films were، contained 0.5% weight، of diamine derivatives which prepared by the method of casting. The photostabilizations، ،of these compounds were determined by monitoring the carbonyl index value with irradiation time. Also, the effect ،of concentrations of additives (range 0.1-0.5wt) on the rate of photostabilization، process was studied. Therefore we found، that a increased photostabilization rates was increase with increasing، concentrations of compound. Besides, the influence، on film thickness، of photostabilization process was also studied; ،and the results، showed that، the increasing of film thickness increase the rate of photostabilization. Also, the changes in the viscosity، of the averagee molecular weight, the degree، of deterioration (α) and the average number of chain scission (s) were tracked, it was concluded، that the random chain scission is always occurs in PVC film, also Quantum yield، of the chain، scission of، these compounds، was calculated. Several mechanisms، have been، suggested and according to experimental results obtained, these mechanisms are dependent on the structure، of، the additive, Among UV absorper، and radical، scavenger.


Introduction:
Polymeric materials were photodegradable when exposed to the ultraviolet radiation, leading to the breaking of polymer،chains, the production، of radicals, reduced the molecular weight، and also caused the deterioration، of mechanical properties، and changed to the unfeasible materials, after an predictable time (1).Poly(vinyl،chloride)i is one،of the world's،most comprehensive plastic materials because of valuable properties, wide-ranging applications, great chemical resistance, barrier properties, low price.(2,3) Vinyl chloride monomer and its polymers occupy a unique place in the history of plastics.When synthetic resin technology was reached early, it was not displaced by newer polymers.Poly(vinyl chloride) is second، only of polyethylene among the five kinds of general plastics materials, which was widely used، in industries including electronic, architecture, chemical engineering, packaging and transportation (4,5). 1

Al-Mustansiriyah
University, Science College, Chemistry Department, Baghdad, Iraq . 2 Al-Mustansyriah University, College of Education, Physics Department, Baghdad, Iraq .* Corresponding Author: olfat_nife@yahoo.comPoly(vinyl، chloride) may degrade in the presence، of oxygen and during processing, storage، and utilization when exposed too high temperatures, high mechanical، stresses or ultraviolet radiation،Polymer degradation took place by the1successive elimination of hydrogen chloride (hydrochloric acid), which1 is called dehydrochlorination, resulting in long polyenes, which thus caused discoloration, deterioration of1 mechanical، properties and، reduction of chemical resistance (2).The low cost and outstanding performance of poly(vinyl chloride) make it a very gorgeous and appropriate plastic for a wide، range of،applications (6).However, PVC suffers from poor، thermal1 and light stability.1Itundergoes rapid، autocatalytic1 dehydrochlorination، upon exposure to heat and lighttduring1 its molding and1 use respectively1(4).As a1 result, conjugated polyene sequences were formed from the beginning of the reaction, ، and they1 gave rise to discoloration of the polymer1and seriously changed its physical1properties.Degradation also caused a strong change in the mechanical properties of the polymer, which was attended1 by، a decrease1 or، increase1 in its average molecular weight as a result of either chain scission or crosslinking of the polymer molecules, respectively (7).
To avoid the ultraviolet degradation occurring in plastic materials،, there are، several ways, including the use of stabilizers1 absorbers or، blockers1.For many outdoor،1applications, the simple addition،, of carbon black at around،, a 2% level, will provide thee protection, for the structure، by the 1blocking، process.Other 1pigments such as titanium dioxide can،1also be effective.1Organiccompounds such as benzophenones and benzotriazoles are typical absorbers which selectively absorb the UV1and re-emit at a less harmful ،wavelength, mainly1 as heat.The1benzotriazole type، is good, as it has a1low color and can be used at1low dose rate1below 0.5%.The1other main1 mechanism for protection is to add a stabilizer ،the most common being، a HALS، (hindered1 amine، light stabilizer).These1 absorb، the excited groups، and stop the1chemical، reaction of the1 radicals (8).As a possible way، to solve the problem of polymer stabilization, a number of different stabilizers have been successfully used (9,10) Organic UV-stabilizers, generally with small molecular weight,1include fluorescent compounds,1phenyl-ester of1benzoic acid, hydroxyl benzophenone,1benzotriazoles, etc (11) A number of heterocyclic compounds including1poly dentate1amines,1crown ethers, bipyridines, naphthyridines , 2-aminobenzothiazol and 2-mercaptobenzothiazole have been1bounded with mainly polystyrene, divinylbenzene copolymers1or linked with1poly(vinyl chloride) (12,13).

Irradiation Experiments: Method of Preparation Films:
The poly(vinyl chloride) (supplied by Petkim Company in Turkey) was dissolved in tetrahydrofuran solvent, left until dissolve then reprecipitated by adding drops of methanol.The solid material was filtered and dried under vacuum at laboratory temperature for124 hours.The poly (vinyl chloride) films were prepared at (40 μm) thickness (measured by a1micrometer Type12610 A, Germany, using a stationary concentration1of poly(vinyl chloride)1solution (5g/100ml) in tetrahydrofuran.The evaporation technique at room temperature for،124 h was used to1prepare thee1films.The poly( vinyl chloride)1films were dried1for1(3 hours)1at room temperature to1remove any tetrahydrofuran residues.The films1 were fixed on1stands1specially used1 for irradiation.The stand was provided1 with an aluminum1plate (0.6 mm in1 thickness) supplied،by1Q-panel company (8,20).

Accelerated Testing Technique:
An accelerated1weather-meter Q-panel1Laboratory ultraviolet (QUV; Q-Panel1Company, Homestead1, Florida1, 1USA) for1irradiation1of poly(vinyl chloride)1films and provided by Q-plate company has been used.The accelerated weathering test included a stainless steel plate that has1one1hole in the1back1side and1two others in the1front.1Eachside1contained lamp (type Fluorescent Ultraviolet Lights) 40 Watt each (Q-Panel Company), giving wavelength range between (250 to380 nm) and the maximum wavelength light intensity was at (6.4 x 10 -7 Ein dm -3 S -1 ).The poly vinyl chloride films were fixed1 parallel to the1lamps and vertically to1make sure1that UV1incident1radiation is perpendicular on the samples, the irradiated1 films1 were rotated1 from time1 to time to، 1ensure that the 1intensity، of 1light incident on1all samples is the same.The distance between the polymer films and the source was (10cm) (21).

Determination of Viscosity Average Molecular Weight by Using viscosity:
It is one of1the most1precise1measurements in1polymer1science and1also the simplest and cheapest.Intrinsic viscosity, which is measured from the flow time of a solution1through a1simple1glass capillary, has considerable historical importance for establishing1 the very existence of1polymer molecules.It also provides considerable physical1 insight.The viscosity measurement was1used to determine the molecular1 weight of polymer, using the Mark-Houwink relation equation( 2 The quantum yield، of main chain scission (фcs) was calculated from viscosity measurement using the following relation (25): Where:" C = concentration, N =Avogadro's number, (Mv,o ) = the initial viscosity average molecular1 weight, [ηo] =Intrinsic viscosity of1PVC polymer1before irradiation1, I o = Incident intensity (6.4 x 10 -7 Ein.dm -3 .s - ) and t = Irradiation time in second."

Results and Discussion: Photodegradation Mechanism for PVC
The PVC photochemical degradation steps are summarized as shown1below(23):-1) When PVC is photolyzed in the presence، of (O2), (the excited، singlet polyenes occuring.Those excited states homolytic cleavage of the (C-CI) bonds happening, the formation of free radicals, [I] and Cl.
Figure 1: FT-IR Spectra1 of PVC (control) at (40 µm thickness) under UV degraded for different exposure time.The absorption bands appearing at (1720 cm −1 )1was attributed to the formation of the (C=O) groups.In the present work the photostabilization of poly(vinyl، chloride)1was examined with additive concentration which weight ranges from (0.1 to 0.5%).The1thickness of1the films PVC was1kept constant at (40μm). Figure (5)(6)(7)(8) show that both of carbonyl index (I CO ) with1irradiation time for PVC films containing1different concentration on additives.The results fig.5-8 show that the carbonyl index (I CO ) are decreasing with increases weight ratio concentration of additives and show that additive concentration of 0.5% by1weight gave the 1best results (27).Such1 a concentration has been applied successfully for photo stabilization of PVC films with other additive (10).1However in Figure (9), the (Ico) of C1, C21, C3 and C4 indicated a lower CO growth rate with\ irradiation\ time for1the PVC control film in the absence of1 any additives.1Since،the growth of the carbonyl index (Ico) with irradiation time was lower than1 the PVC control (Fig. 9), it was1concluded، that such1additives1could be considered as photostabilizers for the PVC polymer.In principle, a1longer induction period is a sign of an efficient1 photostabilizer.Therefore, the C4 is considered to be the most efficient، photostabilizer, followed by C3, C2 and C1.

Determination of average molecular weight using viscometry method:
As a consequence، of photo-oxidation1 degradation1 in PVC is the reduction1of the average molecular1 weight1 of the polymer1 which1 is a result1 of photolytic1 chain1scission.The changes in the molecular، weight  ̅  , of PVC films، with and without additive after irradiation with light1 intensity1 of (6.4 x 10 -7 Ein.dm -3 .s - ) were monitored by1 viscosity1 measurement using equation ( 2) and THF as solvent at 25 ο C.The values of constant in this equation(K=1.5×10 - g/ml, α'=0.77),whenPVC films (with or without additive) were exposed to irradiation the intrinsic، viscosity and viscosity، average molecular weight، decrease with the increase of irradiation time (22,23).Figure (13) shows the relative changes in the viscosity averagee molecular weight ( ̅  ) with irradiation1 time for PVC without and with 0.51% of additives, this figure indicates a1rapid decrease in ( ̅  ) initially then it1slows1down1suggesting1 that the1initial rapid drop1in1 ( ̅  )1is due1to scission of bonds1 at various weak links، that distributed along the polymer chain.The number1 average1 chain1 scission1 (average1 number cut1 per single chain) (S) was calculated by using1 the equation ( 7) : M ̅ v o and M ̅ v t , are the viscosity averagee molecular weights before and after irradiation respectively.The plot، of (S) versus time is shown، in figure (14).The relation indicates،an increasing in the degree of branching which might arise،from crosslinking occur.The degree of deterioration (α) changes with time according،to the following equation (8). =   ̅    .………….(8) Where m and  ̅   are the molecular weights of the monomer1and polymer before irradiation respectively.The plot of  as a1function off irradiation time1is shown، in1 fig.15.The curves indicate1that the degradation is taking place by the random1breaking of bonds1in the polymer chain.Another way in measuring the extent of the degradation1 reaction1 characterization1 is the measurements1of the quantum1 yield1 of the chain scission1(Ф cs ) (28) The quantum1 yield1 of chain scission1(Ф cs ) was1calculated1and tabulated as shown in Table (2) for PVC film without additive and PVC films withe (0.5% wt/wt) of additive mentioned 1above using1 the equation ( 6).

Suggested mechanisms of photostabilization of PVC by diamine derivatives:
The action of (1,1 -Bis (4-aminophenyl) -4-Phenyl Cyclohexane ) derivatives [Schiff base ,1, 3-Oxazepine] as photostabilizers in PVC films1 might be attributed to absorption1by this additive and dissipation on this1energy to harmless1heat energy.The rings of additives in these compounds play role in the mechanism of the stabilizer process by acting، as UV absorber schemes (1,2).
the present1 work, the1 photodegradation rate of1 PVC films was studied1 in1different thickness of (40, 70, 100 μm)1without and1 with fixed concentration of1 (0.5%)1of 1additive.1Therelationship between the carbonyl index with irradiation time are shown in fig.9-11.The results shown in fig.9-11 indicated that the rate of photo-oxidation1(carbonyl indices) at fixed irradiation time steadily decreases with the increasing\ of 1film thickness for (0.5 wt%) additive used and so1 dose that of the PVC control.Therefore, 1one could1 expect1 that the1 slope of 1the relationship1 between1 index with film thickness fig.121varies1with the1type of 1additives1since the 1interaction mechanism1 of1these1different oxygen or1oxygenated 1polymer1materials are certainly different.Figure(12) shows the relationship between1the carbonyl1index1(I CO ) with thickness film which indicates the decreases of photodegration1with the1increaseing of thickness1of the film.

Figure 11 .
Figure 11.The relationship1 between carbonyl1 index and irradiation time1 for PVC films with thickness (100 μm) and that containing1 0.5 wt% of additives.

Figure 13 .
Figure 13.Change in the viscosity average molecular weight ( ̅  ) during irradiation1of PVC films(40µm in thickness) (control) and with 0.5% of additives.