Morphology and Performance of PolyVinyl Chloride Thin Films Doped with Polyorganosilanes against Photodegradation

The importance of polymeric additives has taken an important role in industrial technology and its development and the increase in the consumption period of industrial products, especially plastic products. Therefore, a different type of polymeric additive was used, which can be classified as another type of polymeric additive, where three types of polymers were synthesized as polymeric additives. These polymers differ from each other only in stereo geometry. Three geometric shapes of the polymer were synthesized, namely, ortho, meta, and para polymers. They were studied as photo stabilizers for PVC and compared as the best photostabilizer for PVC. Polyorganosiloxane was invented by various technologies. Polyorganosilanes and poly(vinyl chloride) (PVC) were combined to create homogeneous films. Various methods were used to investigate the effects of long-term irradiation on polyorganosilane-containing films. The development of side products containing polyene and carbonyl groups was observed in the infrared spectra of PVC films before, during, and after irradiation. The absorption bands' intensities of the functional groups associated with the polyorganosilanes were lower when it was present. Furthermore, it was observed that the weight of PVC films dropped less when irradiating them after hybridization with polyorganosilanes. In the presence of polyorganosilanes, there was also a minor alteration in the surface of irradiated PVC. Photodegradation of PVC is inhibited by polyorganosilanes. Hence, the role of polyorganosilanes to stabilize PVC against UV exposure has been studied.


Introduction
Many synthetic and natural polymers absorb ultraviolet rays from the sun. Recently, the use of polymeric materials has increased significantly in many research studies. However, it has been proven that the rapid photodegradation of these materials may affect their efficiency and durability when exposed to natural atmospheric factors [1]. Usually, the damages caused by the continuous exposure of the surfaces of these polymers materials to UV sunlight are the main cause of discoloration of dyes and pigments, such as yellowing of plastics, deterioration of mechanical properties, loss of gloss, and other problems. Therefore, the plastics, paints, cosmetics, and contact lenses industries are keen to offer products that are durable and unchanged for long periods under conditions of exposure to light [2]. Generally, the most common applications of polymers are used to reduce image damage and to maintain life span against outdoor ambient conditions. The use of plastic has contributed to the development of construction applications due to the ease of use of plastic components compared to metal, mortar, glass, wood, and other materials, as well as its low cost. Plastic is also routinely used as outdoor furniture [3]. It is worth noting, that the most common applications of polymers are used to reduce image damage and to maintain life span against outdoor ambient conditions [4]. In particular, PVC is an interesting polymer due to its consideration as a thermoplastic material, which makes it a basic material for many industrial applications [5]. The continuous exposure of PVC to sunlight and high temperatures would affect its thermal and photodegradation to cause major problems in industrial processes [6]. Equally important, studying thin film particles with specific morphologies has acquired an extensive interest by researchers to develop an advanced optoelectronic application [7]. As a matter of fact, the presence of novel surface structures such as belts, honeycombs, plates, rods, flowers, tubes, wires, and porous nanostructures arranged between the metal-semiconductor interface induces the photo-response, reverse saturation current, and, diode quantum efficiency [8]. The superior surface-to-volume ratios, optical charge carriers, longer lifetimes of better electrical conductivity at the M/S junction, and faster light absorption are all attributed to this behavior. On the other hand, the honeycomb/non-porous morphology is of particular importance because it provides better mechanical toughness, a better charge absorber, and has a lower density with a larger diffusion coefficient [9]. Many recent technology applications can modify Honeycomb's distinctive features [10]. The current project deals with the use of polyorganosilanes to stabilize PVC against the negative effects of the irradiation process. This material is aromatic in composition and contains a high percentage of heteroatoms such as (Si; O and N). Therefore, polyorganosilanes are expected to act as good stabilizers to prevent the photodegradation of PVC.

Preparation of PVC Films
PVC solution was prepared after dissolving (5 g) of PVC in tetrahydrofuran (100 mL) solvent and stirred for 30 min at ambient temperature. (0.5 wt %) of Polymers 1-3 was added to the PVC solution and mixed via stirring for 30 min at 21-23 °C. The mixture was poured into glass molds and allowed to evaporate for 24 h at ambient temperature. polymers 1-3 were fully miscible with PVC.

Q.U.V Accelerated Weathering Tester
Q.U.V Accelerated Weathering Tester was utilized to irradiate PVC films with UV light (λ max = 313 nm and light intensity = 6.43 × 10 -9 ein. dm -3 .s -1 ) at ambient temperature (26,200 FIRST ST., CLEVELAND, OH44145 USA) Q-panel Company. The weight loss and gel percentage of the timeradiated films were determined by exposure to UV radiation.

FTIR Spectrophotometry
Photo-oxidation of PVC causes conjugated carbon double bonds and hydroxyl radicals [11]. The degree of photodegradation is determined by changing the intensity of carbonyl (1722 cm1) and polyene (1602 cm1) peaks in the IR spectra for PVC after irradiation. The C-C bond within PVC chains has the effect of giving a reference peak at 1328 cm −1 [11]. This peak was not affected by UV irradiation. The functional group index (I S ) for each functional group was calculated through Eq. (1), where A is the peak absorbance for a specific functional group and Ar is the absorbance for the reference peak:

Synthesis of Polymers 1-3
Polymers 1-3 were synthesized as studied [12] from the reaction of organosilicons and benzidine while heating THF to its boiling point. This reaction is catalyzed by glacial acetic acid for 5 h to produce the corresponding polymers 1-3 in 79-85% yields (Scheme 1). The structures of the mentioned polymers were found with the evidence and are consistent with those reported.

Using an FT-IR spectrometer
The effectiveness of polymers (1-3) as optical stabilizers for PVC films was studied by FTIR spectroscopy when UV light is applied to them. Infrared peak intensity and the wavelength of different functional groups (e.g., carbonyl, polyene, hydroxyl) after irradiating PVC film are shown in Fig. 1.
In general, FTIR bands spectra at 1722, 1602, and 3500 cm −1 of PVC films are attributable to aliphatic ketones, (1) I s = A s ∕A r carbonyl group double bond, and hydroxyl groups of alcohol, respectively [13]. By studying the variation of adsorption energies in carbonyl, alkene, and hydroxyl groups during the irradiation, the photodegradation process of PVC was verified [14]. The functional groups' intensity peaks fluctuated when compared to the standard peak (1328 cm −1 ). These functional groups' intensities (I C=O and I C=C ) were calculated and plotted as a function of irradiation time as displayed in (Figs. 2 and 3). The indices of both C = O and C = C for PVC films with the thickness (40 μm) with the polymers (1-3) (0.5 wt %) were lower than the indices of the blank PVC film with the thickness (40 μm). Adding polymers 1-3 restrain photodegradation significantly which can be used as long-term protection additive for PVC films against irradiation.

By Weight Loss
In general, there are limitations to adding low molecular weight organic UV stabilizers to polymeric materials. This is because the addition of these polymers will cause problems such as incompatibility, volatility, and migration [14]. Therefore, UV stabilizers with high molecular weight are a better choice for irradiation protection of PVC. The PVC films with organosilane polymers (1-3) (0.5 wt %) were irradiated for 300 h.  Where the percentage of weight decrement was calculated and plotted against irradiation time (Fig. 4). the percentage of PVC weight loss was lower in the presence of PVC + polymer 1 and the highest for PVC without adding any polymer.

Scanning Electrons Microscopy (SEM) Analysis
The effect of UV radiation on the surface morphology of PVC films was studied in SEM studies [15,16]. The SEM images of the PVC film are shown in Fig. 5. The blank PVC film before exposing to radiation was fine and smooth. However, the damage to the PVC (blank) surface occurred after 300 h of irradiation. The damage was obvious compared to the PVC surface that contained polymer additives.
UV damage is usually the main cause of deterioration of mechanical properties, loss of glossiness, discoloration of dyes and pigments, yellowing of plastics, and other problems. On the other hand, manufacturers of plastics, cosmetics, paints, and contact lenses are keen to provide products that resist prolonged exposure to light. Most common applications of polymers are utilized to reduce photodegradation damage and to maintain a life span against outdoor ambient conditions [17,18]. In addition, deep cracks are formed on the surfaces of these polymeric films when irradiated due to the decomposition of molecules and hydrocarbon polymer chains damaged as a result of exposure of these surfaces to continuous irradiation compared to the surface of the non-radioactive film [15]. Another key point is that the surface of the blank PVC film has been damaged compared to the damage seen in PVC films containing (1-3) after irradiation as shown in Fig. 6. The SEM image of the PVC + 1 film reveals the least damage to the surface after the irradiation process as displayed in (Fig. 6a). Furthermore, the 3D structures of the fabricated porous 3D structure (PVC + 3) film shown in (Fig. 6c) were identical to each base urethane form. The pore size of the fabricated porous film tends to be slightly bigger when hydrogen chloride (HCl) was eliminated, causing discoloration [16].

Energy Dispersive X-ray
The polymeric material structure was determined by the EDX technique with SEM for determining the chemical components of the PVC film on a micro-or nanoscale [15]. The EDX data shown in Fig. 7 were for the blank PVC film composites.
The PVC film EDX patterns containing polymers 1-3 are shown in Figs. 8 (a-cIt's clear that the EDX data in Fig. 8 (a-c) presented a new band for PVC-containing polymers (1-3) which was relevant to the existence of nitrogen atoms within the added polymers. The characteristics match the previous work on PVC using the EDX technique [15]. This study showed the increase in the atomic ratio of oxygen via increasing the irradiation time. This arrangement illustrates the important role of photo-stabilizers in inhibiting the release of chlorine atoms into the form of hydrogen chloride, which is an essential catalyst for photo-oxidation. Additionally, to reduce the process of photo-degradation to the building units of carbohydrates chains within the polymer [19].

X-ray Mapping
X-ray images of PVC and organosilane polymers (1-3) are displayed in Figs. 9, 10, 11, 12 respectively, showing the distributions of the elements and their relative abundance in PVC films [15]. Long-term exposure of PVC membranes to UV light causes dechlorination which results in hydrochloride production from the polymer chains and hence the abundance of chlorine inside PVC films [20,21]. On the other hand, polymer additives represented by organiosilane reduce the self-release of hydrogen chloride. Thus, this leads to reducing the excess oxygen produced by the light portion represented by peroxides and hydroperoxides through the process of stabilizing free radicals through polymers and then reducing their photo-degradation catalytic activity [22].

The Effect of Light on Polymers
Photodegradation is conducted when materials are subjected to sunlight, especially in the ultraviolet region Rabek wrote a comprehensive review of the mechanisms of photodegradation in polymers [23]. Photodegradation mechanisms are briefly described in this section. Photodegradation can be carried out in the air or in an inert atmosphere and is called photo-oxidative degradation [24].

Inhibition of Photodegradation of Graphene in PVC
Light irradiation is a catalyst for several decomposition reactions which are carried out for several industries such as petroleum and petrochemical products. Industrial products have different ways of being affected by photo-radiation. In general, photo stabilizers play an important role in organic components and polymer compounds. Therefore, researchers need to understand the mechanism of photodegradation. In particular, the photodynamic interactions are believed to initiate from some unstable polymer structures. On the other hand, photo-degradation reactions are often associated with oxidative decomposition reactions [11][12][13][14][15].
Based on the steps of photolysis reactions, the following are the three categories of optical stabilizers:

A-Light Shields B-Quencher dampers C-Peroxide Decomposers D-Radical scavenging
Organosilane polymers used as photo stabilizers when irradiated acted uniformly in PVC blends. Various mechanisms have been proposed to explain the role of organic polymers in PVC photo-stabilization [25]. The attraction potential between the CH = N bonds of the polarized organic polymers and the polarized C-Cl bonds within the PVC chains can stabilize PVC (Fig. 13) by efficiently transferring the energy of the excited PVC to the organosilane polymers. After then, the organosilane polymers can release the energy required to heat over time which does not damage the polymeric PVC chains.
Aromatic organic polymers absorb light to act as optical stabilizers. This occurs without dissolving or catalyzing reactions of dissociation of the polymers. The energy quenchers are responsible for converting organic polymers into harmless thermal energy [26,27]. Where the role of this energy is to stabilize the polymers as shown in (Fig. 14) by direct absorption of ultraviolet.
Moreover, adding aromatic organosilane polymers scavenges free radicals that generate molecules such as hydroperoxides, which are commonly known as peroxide decomposers. It causes the photo-degradation of hydrogen oxide and turns it into active free radicals that Fig. 8 (a-c). EDX spectra of PVC + polymers (1-3) after irradiation for (300 h) with ultraviolet light contribute to pyrolysis reactions. Finally, it has been discovered that Organosilane polymers also act as optical stabilizers to scavenge the radical in the presence of a color carrier (POO •) to stabilize PVC. These polymeric additives can seize the free radicals resulting from the photolysis of some peroxides and hydroxides (Fig. 15) [14,15].
The CH = N bonds and aryl moieties in polyorganosilane 1-3 play an important role in stabilizing the PVC against photodegradation. However, it is believed that the ortho-group attached to aromatic moieties within polyorganosilane 1 makes such an additive an efficient radical scavenger compared to the other polyorganosilane. Various mechanisms were suggested to explain the role that polyorganosilane could have in the photo stabilization of PVC films. Polyorganosilane could then release such energy to heat over time, which does not harm the PVC polymeric chains. However, the steric hindrance could     [18][19][20]. Furthermore, Polyorganosiloxane acts as a barrier that will hinder the diffusion of low molecular compounds such as Oxygen. At the same time, graphene's existence in the polymer matrix creates winding pathways that make oxygen and free radicals hard to diffuse into the polymer structure. Therefore, the rate of the first reaction in the propagation stage (which is controlled by diffusion) decreases, resulting in a slower rate of photodegradation. Figure 16 demonstrates the distinction between an oxygen-containing and a pure polymer. This allows us to identify how the diffusion pathway of oxygen is longer when polyorganosilane is present. This protective mechanism is affected adversely when used for photo stabilization because of the decrement of the aspect ratio of carbon black isotropic particles' activity.

Conclusions
Three highly aromatic polyorganosilanes were created by using an efficient and simple synthetic procedure. The structure of polyorganosilanes was approved by  different analytical and spectroscopic methods. Polyorganosiloxane acts as photodegradation inhibitor for PVC, especially when exposed to long-range ultraviolet radiation. Polyorganosilanes tend to reduce the formation of hydrolyzed byproducts, reduce weight loss and average molecular weight, and damage the polymer face. The polyorganosilanes were effective at reducing the rate of dehydrochlorination process by reducing azomethane. Polyorganosilanes are more efficient in absorbing UV radiation.