Ultra violet spectra studies of polystyrene films in presence of some transition metal complexes with 4-amino-5-pyridyl)-4h-1,2,4-triazole-3-thiol

Introduction

Triazoles are five memberd heterocyclic compounds containing three nitrogen and two carbon atoms. The substituted triazole with sulphur atom and amine group are considered to be good coordinating ligands because they involved both hard nitrogen and soft sulfur atom as thio amide group, this ligand have doner group that coordinate with wide range of metal ions (Al-Maydama et al. 2008), (Narayana and Gajendragad , 1997). In this paper some complexes of substituted 1,2,4 triazol with thio and amino group has been used as photostabilizer for polystyrene. The low cost and the good performance of PS products have increased the utilization of this polymer in building and other application, it is a multipurpose polymer that is used in varied applications include rigid item. General purpose polystyrene is clear and hard which is used in packaging, laboratory ware, and electronics (Meenakshi et al. 2002). One of the important uses of PS is in the manufacture of cover signal lamps of some automobiles (Safy Eldin and El-laithy, 1994), (Yousif  et al. 2013 (A)). The photooxidative degradation processes of PS have been discussed in a number of reviews (Rabek and Ranby, 2003), (Lawrence and Weir, 2003).  It is generally accepted that carbonyl formed during UV irradiation of polymers, is most probable and are responsible for the yellow coloration of the polymer (Mori et al. 1979). The carbonyl groups generated during the photooxidation process of polymer, extend the polymer film absorption to longer wavelengths. These groups absorb light when they irradiated with light of wavelength between (200-700 nm) and activated to the singlet and triplet excited states which enhances various successive photooxidation reactions (Cooray and Scott, 1980). The physical properties of additives and polymers play a very important role in determining the additives efficiency in photostabilization or photodegradation of polymers. For example, the compatibility that any type of additive (photostabilizer, antioxidant, thermal stabilizer…. etc.) must be evenly distributed which requires that it be compatible with the polymer matrix (Gugumus, 1979), (Yousif and Haddad, 2013). In this work the photostabilization of PS was studied by using five complexes of 4-amino-5 (pyridyl)-4H-1,2,4-triazole-3-thiol.

Experimental

Materials

The following complexes were all prepared by the method described in this reference (Haddad et al., 2013):

These complexes are:

1. Bis(4-amino-5-(pyridyl)-4H-1,2,4-triazole-3-thiol) Nickel(II), Ni(L)₂ .
2. Bis(4-amino-5-(pyridyl)-4H-1,2,4-triazole-3-thiol) Cupper(II), Cu(L)₂ .
3. Bis(4-amino-5-(pyridyl)-4H-1,2,4-triazole-3-thiol) Zinc(II), Zn(L)₂ .
4. Bis(4-amino-5-(pyridyl)-4H-1,2,4-triazole-3-thiol) Cadmium(II), Cd(L)₂ .
5. Bis(4-amino-5-(pyridyl)-4H-1,2,4-triazole-3-thiol) Tin(II), Sn(L)₂ .

The structure of complexes has been shown in figure (1):

Figure1: The proposed structure of Complexes.Click here to View figure

 

Experimental techniques

 Films preparation

A solution of polystyrene (5% w/v) in chloroform was used to prepare (40µm) thickness of polymer films. The films were prepared by evaporation technique at room temperature for 24 hours, to remove the possible residual chloroform solvent. After the evaporation of solvent, that’s led to formation of PS films. The thickness of these films is about 40 μm. Modified PS can be prepared by mixing of 0.5% by weight complexes to the solution containing polystyrene (Yousif et al., 2012), (Yousif et al., 2013 (B))

Irradiation Experiments                                                                         

Accelerated Testing Technique

UV- Light was used for irradiation of PS films, giving wavelength range between (250 to 380 nm) and the maximum wavelength light intensity is at 6.2 X 10^-9 Ein Dm^-3 S^-1. The polymer film samples were fixed parallel to each other and the lamp of the UV. incident radiation is vertically incident on the samples. The distance between the polymer films and the source was (10 cm). (Yousif et al., 2011).

Photodegradation measuring methods

Measuring the photodegradation rate of PS films by using ultraviolet–visible spectrophotometer:

The ultraviolet-visible spectrophotometer type Shimadzu UV-VIS. 160 was used to measure the changes in the Uv-visible spectrum during irradiation time for each compound at maximum absorption band (l_max). The absorption spectrum was measured in the range of (200-400nm), and the (l_max) at each absorption was also recorded for different irradiation times.

The infinite irradiation time was considered and the infinite absorption (A_¥) was assumed to be after the infinite irradiation time.

To determine the photodegradation rate constant for photostabilizer (K_d), the first order equation was used:

ln(a-x) = lna – K_d t ……………..(1)

Where a, represent the stabilizer concentration before irradiation, x represents the change in stabilizer concentration after irradiation time (t).

If A_o represents the absorption intensity of the polymer film containing stabilizer before irradiation, A_t represents the absorption intensity after t time of irradiation, then:

a =  A_o – A_∞

x = A_o – A_t

a – x = A_o – A_∞ – A_o + A_t = A_t – A_∞  ………… (2)

Substitution of a and (a – x) from equation (2.6) in (2.5) gives:

ln(A_t -A_∞) = ln(A_o – A_∞) – K_dt   …………… (3)

Thus a plot of ln(A_t – A_∞) versus irradiation time (t) gives straight line with a slope equal (K_d) which indicates that photodecomposition of the additives is first order.

Results and Discussion

Study of the efficiency of prepared Schiff’s basses as photostabilizers of PS films by ultraviolet spectroscopy

Ultraviolet radiations are known to have deleterious effects on most industrial polymers inducing chemical modification and scission of polymer chain, which ultimately lead to an undesirable loss of the mechanical and surface properties of the irradiated material. Photodegradation of PS causes discoloration (yellowing), cross-linking, and chain scission due to oxidation and effect of UV light and heat (Rabek, 1987), (Kiatkamjornwong et al., 1999). UV light induces the production of radicals by oxidation. The prepared complexes were used as photostabilizers to PS films comparing with PS blank. The additives used in this study were chosen to be completely soluble in polymer solvent, (chloroform). It has been notice that the additives used in the present work are photodecomposed during the photolysis. Thus the photo decomposition rate constant (K_d) was calculated. The K_d values were computed using the UV. spectra changes of PS films thickness 40μm containing 0.5% w/w from additives. The plot of irradiation time versus ln (A_t-A ͚ ), gives straight line which indicate primarily the first order reaction. The slope equal to the decomposition rate constant K_d. Figure (2),(3),(4),(5),(6) and (7) shows the variation of ln (A_t – A ͚ ) with irradiation time for all additives in PS films at λ=365 nm.

Figure2: Variation of natural logarithm of ln (At – A∞) with irradiation time of PS (blank) film  Click here to View figure

 

Figure3: Variation of natural logarithm of ln (At – A∞) with irradiation time of Ni(L)2 in PS film   Click here to View figure

 

Figure4: Variation of natural logarithm of ln (At – A∞) with irradiation time of Cu(L)2 in PS film   Click here to View figure

 

Figure5: Variation of natural logarithm of ln (At – A∞) with irradiation time of Zn(L)2 in PS film   Click here to View Figure

 

Figure6: Variation of natural logarithm of ln (At – A∞) with irradiation time of Cd(L)2 in PS film   Click here to View figure

 

Figure7: Variation of natural logarithm of ln (At – A∞) with irradiation time of Sn (L)2 in PS film   Click here to View figure

 

Table (1) Photodecomposition rate constant (K_d) of PS films thickness (40mm) containing 0.5 % of additives

Polymers	Kd (S-1)
PS (blank)	4.365 X10-7
PS + Ni(L)2	7.639 X 10-8
PS + Cu(L)2	2.863 X 10-8
PS + Zn(L)2	3.095 X 10-8
PS + Cd(L)2	1.000 X 10-7
PS + Sn(L)2	2.044 X 10-7

 

The photostabilizers always posses low K_d values, which mean that these modified polymers are stable towards UV light. One could notice that K_d values are sensitive to the type of additives in PS films, which decrease in the following order:

PS > Sn(L)₂ > Cd(L)₂ > Ni(L)₂ > Zn(L)₂ > Cu(L)₂

and this might point out to increase the photostability of this additives in this term.

Acknowledgment

The authors thank Al-Nahrain University and Universiti Kebangsaan Malaysia for the funding (Codes AP-2011 17, DPP-2013-054, UKM-MI-OUP- 2011, AP-2012-017, and DLP 2013-002).

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