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CHEMICAL PROBLEMS 2024 no. 2 (22) ISSN 2221-8688
221
UDC 547.3+615.3
INNOVATIVE METAL COMPLEXES AS PHOTOSTABILIZERS TO IMPROVE THE FUNCTIONAL LONGEVITY OF POLYVINYL CHLORIDE
Husam Salman1, Dina S. Ahmed2, Amir A. Hassan1, Jawad Shnein1, Mohammed Kadhom3, Rania Kareem3, Muna Bufaroosha4,\ Ahmed Ahmed1, Hassan Hashim5, Amani Husain6,
Emad Yousif1*
'Department of Chemistry, College of Science, Al-Nahrain University, Baghdad, Iraq 2Department of Chemical Industries, Institute of Technology-Baghdad, Middle Technical University,
Baghdad, Iraq
3Department of Environmental Science, College of Energy and Environmental Sciences, Al-Karkh University
of Science, Baghdad, Iraq 4Department of Chemistry, College of Science, United Arab Emirates University, Al-Ain, United Arab
Emirates
5Department ofPhysics, College of Science, Al-Nahrain University, Baghdad, Iraq 6Polymer Research Unit, College of Science, Mustansiriyah University, Baghdad, Iraq
* Email: muna.bufaroosha@,uaeu.ac.ae [email protected]
Received 23.12.2023 Accepted 27.02.2024
Abstract: Polyvinyl chloride (PVC) is involved in diverse applications that significantly influence our daily lives; it is industrially synthesized in various configurations in order to fulfill the target application. However, PVC is susceptible to photodegradation, yielding toxic byproducts detrimental to both the environment and human health, which diminishing its utility lifespan. Addressing this concern, current research explores the application of metal complexes as potential photostabilizers to mitigate PVC photodecomposition. The objective of this study is to investigate the effectiveness of formulated metal complexes in preventing photodegradation. Five metals, namely Cu(II), Ni(II), Cd(II), Zn(II), and Sn(II), are included. Examining parameters, such as molecular weight attenuation, the formation of alkene-laden and carbonyl fragments, and the surface morphology alterations of PVC sheets subjected to irradiation are considered. Findings indicate that these metal complexes exhibit remarkable efficacy in decreasing the photodegradation of PVC, thus presenting a promising avenue for extending its functional longevity. The polymer containing Cd(II) complex unit showed the least damage in the PVC surface due to photoirradiation, followed by other complexes.
Keywords: polyvinyl chloride; metal complexes; photodegradation; surface morphology; molecular weight reduction
DOI: 10.32737/2221-8688-2024-2-221-230
1. Introduction
Polymers play a pivotal role in numerous applications owing to their distinctive properties, cost-effectiveness in manufacturing, and adaptability to various forms [1]. Enhancement of polymeric material properties is often achieved through blending and doping techniques [2], resulting in significant modifications to the surface morphology,
structure, physical attributes, and overall performance [3,4]. The efficacious incorporation of metal-containing organic moieties into polymeric materials has been demonstrated to enhance corrosion resistance, durability, and resistance to aging. In particular, the integration of rare-earth oxides-based composite materials showed noticeable
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CHEMICAL PROBLEMS 2024 no. 2 (22)
advancements [5]. As a result, many studies have been published using these materials; yet, additional research is imperative to generate higher efficient polymeric composites suitable for diverse applications [6,7].
The impact of the doping procedure is influenced by diverse factors, where miscibility, particle size, phase segregation, dispersion, and crystalline are the most popular ones [8]. Today, PVC has witnessed a growing global demand due to its distinctive properties and cost-effectiveness production. It is extensively used in many industries, including office supplies, building materials, toys, furniture, medical devices, packaging, tubing, film and sheet manufacture, and more. However, PVC's chlorine content constitutes more than half of its weight, rendering it valuable for insulator production [9, 10]. Also, ultraviolet (UV) light, sunshine, and high temperatures can cause photodegradation [11, 12]. This photodegradation induces alterations in both the chemical and physical properties of PVC, resulting in undesirable changes [13]. Notably, the consequences of PVC photodegradation
encompass mass loss, the hindering of volatile products, and the formation of fragments with lower molecular weights [14-18]. To counteract these effects and ensure prolonged utility, additives are incorporated into the PVC during manufacturing. These additives enhance the photostability of PVC while simultaneously improving its transparency, durability, and color over an extended duration [19, 20]. Various additives at low concentrations have been used to enhance the PVC photostability upon UV irradiation [21]. The most common additives include inorganic salts [22], heterocycles [23] and aromatics [24].
We present here a study of the effective use of pre-synthesized metal complexes as a sequence of our previously published studies [19, 20]. These complexes can serve as novel photostabilizers to mitigate PVC photodegradation when exposed to UV light irradiation. Different techniques were used to study the PVC films and findings showed a remarkable improvement in the photo-resistivity.
2. Materials and Methods
2.1. General
The reagents and chemicals were purchased from Merck of Gillingham, UK. However, the material used was PVC obtained from Petkim Petrokimya in Istanbul, Turkey, with a molecular weight (Mv) of around 180,000. The Fourier Transform Infrared (FT-IR) of spectra range 4000-400 cm-1 was recorded on a Jasco FT/IR-4200 spectrometer (Tokyo, Japan). The PVC sheets were exposed to irradiation at 25 °C utilizing a Q-Panel tester from Homestead, FL, USA, with a UV light with the highest wavelength and light intensity of 365 nm and 6.2 x 10-9 Einstein dm-3 s-1. The sheets were set vertically, 10 cm away from the light source and in line with the UV lamps, while the tester stood on either side of the light with two fluorescent lamps that emit ultraviolet light (UV-B 365, 40 watts). The plastic sheets were rotated regularly to provide even irradiation from all directions. Ostwald U-Tube viscometers (Ambala, Haryana, India) were used to estimate viscosity. Using a FEI Inspect
S50 microscope (Czech Republic), the surface morphology of the irradiated sheets was investigated.
2.2. Synthesis of metal complexes
Metal complexes involving Cu(II), Ni(II), Cd(II), Zn(II), and Sn(II) metals with 2-(6-methoxynaphthalen-2-yl) propanoate were synthesized using the previously established method [19,20], where the structure is illustrated in Scheme 1. The preparation of metallic complexes with 2-(6-methoxynaphthalen-2-yl) propanoate, conducted in a 1:2 molar ratio, resulted in the formation of the respective complexes [19, 20].
2.3. PVC Films Preparation
Mixing 5g of PVC with 25 mg of metal complexes in 100 ml of tetrahydrofuran (THF) allowed the mixture to swirl for two hours. The resulting uniform solution was subsequently doped onto a glass tablet that had 15 cavities measuring around 45 |im in thickness. The tablet was left to dry in air for 24 hours at 25 °C. After that, to make sure that all traces of THF
were completely removed, the films went vacuum oven set at 40 °C. through another drying process for 8 hours in a
MeO
OMe
M= N¡(11), Cu(ll), Zn(ll), Cd(ll) and Sn(ll)
Scheme 1. Synthesis of metal complexes.
2.4. Monitoring the photodegradation of PVC films by FTIR Spectrophotometry
Photodegradation of PVC leads to the formation of tiny plastic pieces with carbonyl (C=O) and alkene (C=C) groups. The main reason for this breakdown is dehydrochlorination, which is the process of removing hydrochloride from the plastic chains [21]. At different irradiation periods, FTIR spectra of the PVC sheets that were exposed to
radiation were recorded. Using the C-H bond as a reference peak at 1328 cm-1 for comparison, the strength of the absorption bands corresponding to the C=O and C=C groups were at 1714 cm-1 and 1618 cm-1, respectively. By plugging the values of the reference peak (AC-H) and the absorbance of the functional group (AC=O or AC=C) into Equation (1), we were able to estimate the functional group indexes (Is, Ic=o, or Ic=c).
As
I = —
Is A
(1)
2.5. Average Molecular Weight (Mv)
We examined the inherent viscosity, abbreviated as [n], of the PVC sheets after dissolving them in THF after irradiation. The
Mv of the irradiated films was determined using the Mark-Houwink equation [22] as shown in Equation (2).
[n] = 1.63 x 10-2 M
2 A/10.766
v
(2)
3. Results and discussion
3.1. FTIR Spectrophotometry
The initiation of radical species, such as chloride and carbon radicals, occurs through PVC photooxidation induced by photoirradiation in an oxygen-rich environment.
These radicals play a critical role in the detrimental degradation of PVC, leading to the formation of volatile byproducts, notably HCl. Consequently, C=O moieties (including chloroketones and ketones) and C=C groups within unsaturated chains are generated in the residual PVC [23]. To evaluate the impact of irradiation on PVC, Fourier-transform infrared
(FTIR) spectroscopy was employed. Throughout the irradiation process, bands corresponding to the vibrations of the C=O at 1714 cm-1 and C=C at 1618 cm-1 groups were observed to increase in intensity. Intensification of these functional groups was compared to a reference peak (C-H bond; 1328 cm-1), which remained relatively unaffected by the procedure [23]. Figure 1 illustrates changes in the vibration band intensities of C=O and C=C observed in the FTIR spectra of pure PVC as a result of irradiation.
v
m
i • |V| V «
\ • \ / ( I \f\ /» 1 ( / !
—J W* 1 11 Mi\l 1 r >' i « /
300 h L in ii V I « IL
N 1 If
¿MO
yon
»m
«Wirrt»» jo»l|
IMC
tiO
Figure 1. FTIR spectra of PVC films: comparison between non-irradiated and irradiated states.
3.2. IC=O and Ic=c of the polymeric films
iC=c oj inepolymericjums during the irradiation process, with the pristine
Following irradiation, the functional PVC case showing the most significant changes.
group indices IC=O and IC=C were calculated Importantly, the increases in IC=O and IC=C were
using Equation (1) and plotted against the relatively smaller for PVC blends containing
irradiation time (Figures 2 and 3, respectively). metal complexes compared to the blank film. Both IC=O and IC=C showed an upward trend
1.8 1.6 1.4 1.2 1 0.8 0.6 0.4 0.2 0
PVC
PVC + Cu(L)2 PVC + Ni(L)2
-•-PVC + Sn(L)2
9 PVC —PVC + Zn(L)2 + Cd(L)2
P k
0 fc— '
w
50 100 150 200 250
UV exposure time (h)
300
350
Figure 2. Alterations in the IC=O Indicator of PVC Films
3.3 Average Mv contributing to this decline in Mv are the chain
The photoirradiation of PVC induces the scission and cross-linking of polymeric chains.
cleavage of small plastic fragments, leading to a The intrinsic viscosity [n] is highly influenced
reduction in the Mv. The primary factors by Mv, consequently anticipating a reduction in
the solution viscosity of irradiated PVC films [24].
100 150 200 UV exposure time (h)
Figure 3. Variations in the Ic=c Indicator of PVC Films.
To assess the impact of irradiation on Mv, PVC films irradiated for varying durations were dissolved in THF, and their viscosities were estimated. The Mv was calculated via Equation (2) and plotted versus irradiation time (50-300 h; Figure 4). The presence of insoluble residues indicated branching and cross-linking during the irradiation process. The Mv exhibited a sharp and continuous decrease with increasing
irradiation time. Notably, all metal complexes consistently mitigated the reduction in Mv. The metal complexes demonstrated a remarkable ability to alleviate the depression in Mv of PVC, providing a high degree of stabilization. Among them, the Cd(II) complex emerged as the most effective PVC photostabilizer compared to others.
150 200 250 UV exposuretime (h)
Figure 4. Fluctuations in the Mv Parameter for PVC Films.
3.4. Scanning Electron Microscopy (SEM) offering insights into their internal structures
SEM serves as a powerful technique for [26]. Electron beams enable the capture of examining the surface morphology of polymers, precise, magnified images of the PVC surface.
Figure 5. SEM images for PVC films
The introduction of metal complexes into the PVC induced an overall alteration in particle size and their ununiform distribution on the surface after 300 hours of UV irradiation. SEM images of the PVC films revealed a notable rough surface post-irradiation, indicating a noticeable alteration in PVC surface
morphology. Images of PVC blended with various metal complexes illustrated that irradiation had only a minimal impact on the compact texture, which is clarified in Figure 5. The films containing additives exhibited high resistance to irradiation, demonstrating excellent chemical stability in the blends.
Me
MeO
+ MCI2
M= Ni(ll), Cu(ll), Zn(ll), Cd(ll) and Sn(ll)
Scheme 2. Proposed Mechanism for Photostabilization of M(L)2 Complexes as HCl Scavengers.
3.5. Proposed mechanisms for PVC photostabilization
Several proposed mechanisms for the photostabilization of polyvinyl chloride (PVC) have been elucidated in the literature. The efficacy of Bis[2-(6-methoxynaphthalen-2-yl)propanoate] complexes as stabilizers for PVC sheets can be evaluated by analyzing changes in concentration indices, as supported by extensive documented data. These complexes act by forming covalent carboxylates, which in turn stabilize PVC through mechanisms reliant upon the strong Lewis acidic properties of the associated metals. Furthermore, these stabilizers exhibit the additional function of scavenging hydrogen chloride (HCl) and facilitating the replacement of allylic chlorine atoms with carboxylate groups [25]. Typically classified as secondary stabilizers, they demonstrate
exceptional long-term stability, as depicted in Scheme 2.
Metal carboxylates serve as effective substitutes for allylic chlorine in PVC stabilization, as suggested by infrared spectroscopic analyses indicating their interaction with PVC molecules at the main particle morphology [25]. This pivotal role in the stabilization process designates these complexes as primary stabilizers. 3.6. The quantum (@cs) yield of PVC films' chain scission
The quantum yield of chain scission (®cs) serves as an alternative method for quantifying degradation processes. The quantum yield for chain scission in modified PVC films can be calculated using the equation provided in [26]. The corresponding Ocs values for these polymers are presented in Table 1.
Table 1. Quantum yield (®cs) for the chain scission for 40 ^m thick PVC sheets after 300 h irradiation
time before and after filling the complexes
Additive The quantum yield of main chain scission (Ocs)
PVC 5.14E-05
Zn(L)2 1.46E-07
Sn(L)2 1.35E-07
Ni(L)2 2.88E-07
Cu(L)2 3.71E-07
Cd(L)2 1.28E-07
The relatively low values of Ocs can be attributed to the phenomenon of energy absorption at a single site followed by dispersion of electronic excitation across numerous bonds within the extensive PVC molecule. This dispersion mechanism diminishes the probability of individual bond breakage or may result in the dissipation of absorbed energy through non-reactive pathways. It is well-established that elevated temperatures often correlate with increased Ocs values,
particularly in proximity to the glass transition temperature (Tg) for amorphous polymers and the melting point for crystalline ones [26]. In the context of this study, PVC film undergoes photolysis at temperatures ranging between 25 and 40 °C, which notably falls below the Tg of PVC (80 °C). Consequently, it is not anticipated that temperature will exert a significant influence on Ocs values in this experimental setup.
4. Conclusions
In the present study, the photostabilization of PVC sheets employing Bis[2-(6-methoxynaphthalen-2-yl)propanoate] complexes was investigated. These additives exhibited notable efficacy as photostabilizers for PVC films, primarily functioning through effective
HCl scavenging mechanisms. Notably, among these additives, the cadmium complexes emerged as particularly efficient in the photostabilization process, as evidenced by the observed enhancement in photostability and the elucidated underlying mechanism. This finding
underscores the potential utility of cadmium stabilizers in PVC applications. complexes as viable candidates for commercial
Acknowledgment
The authors like to thank Alnahrain University for partially supporting this work.
Funding
None. Conflict of Interest
The authors declare there is no known conflict for this work.
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POLMNiLXLORiDiN FUNKSiONAL DAYANIQLILIGINI ARTIRMAQ UCUN iNNOVATiV METAL KOMPLEKSLORiNiN FOTOSTABiLiZATOR KiMi TOTBiQi
Husam Salman1, Dina S. Ahmed2, Amir A. Hassan1, Cawad Shnein1, Mohammed Kadhom3, Rania Kareem3, Muna Bufaroosha4, Ohmad Ohmad1, Hassan Hashim5, Amani Husain6, Emad
Yousif1*
1 dl-Nahreyn Universiteti, Elmlar Kolleci, Kimya Departamenti, Bagdad, iraq
2Kimya Ssnayesi Departamenti, Texnologiya institutu-Bagdad, Orta Texniki Universiteti, Bagdad, iraq 3dtraf Mühit Elmlsri Bölmssi, Enerji vs dtraf Mühit Elmlsri Kolleci, dl-Ksrx Elm Universiteti, Bagdad, iraq 4 Kimya Departamenti, Elmlsr Kolleci, Birls§mi§ drsb dmirliklsri Universiteti, dl-Ain, Birls§mi§ drsb
dmirliklsri
5 Fizika Departamenti, Elmlsr Kolleci, dl-Nshreyn Universiteti, Bagdad, iraq 6Polimer Ara§dirma Bölmssi, Elm Kolleci, Mustansiriyah Universiteti, Bagdad, iraq *E-mail: [email protected] [email protected]
Xülasa: Polivinilxlorid (PVX) gündalik hayatimiza ahamiyyatli daracada tasir edan müxtalif tatbiqlara malikdir va sanaye üsulu ila müxtalif konfiqurasiyalarda sintez olunur. Bununla bel a, PVX fotodeqradasiyaya ugrayaraq ham atraf mühita, ham da insan saglamligina zararli alava mahsullar amala gatirir va bununla da onun yararliligini azaldir. Bunlari nazara alaraq, i§da PVX-in fotodeqradasiyasini azaltmaq maqsadila metal komplekslarin potensial fotostabilizatorlar kimi tatbiqi ara§dirilmi§dir. Fotodeqradasiyanin qar§isinin alinmasinda polimerin molekul kütlasinin azalmasi, alken yüklü, karbonil fraqmentlarinin formala§masi va §üalanmaya maruz qalan PVX tabaqalarinin sath morfologiyasi kimi parametrlarin ara§dirilmasinda metal komplekslarinin effektivliyi tadqiq edilmi§dir. Müayyan edilmi§dir ki, bu innovativ metal komplekslari polivinilxloridin fotodeqradasiyasini azaltmaqda effektivlik nümayi§ etdirir va belalikla, onun funksional uzunömürlülüyünü artirmaq üfün perspektivli ola bilar.
A^ar söztari: polivinilxlorid; metal komplekslari; fotodeqradasiya; sath morfologiyasi; molekulyar ?akinin azalmasi
ИННОВАЦИОННЫЕ МЕТАЛЛОКОМПЛЕКСЫ КАК ФОТОСТАБИЛИЗАТОРЫ ДЛЯ ПОВЫШЕНИЯ ФУНКЦИОНАЛЬНОЙ ДОЛГОВЕЧНОСТИ ПОЛИВИНИЛХЛОРИДА
Хусам Салман1, Дина С. Ахмед2, Амир А. Хасан1, Джавад Шнейн1, Мохаммед Кадхом3, Рания Карим3, Муна Буфаруша4, Ахмед Ахмед1, Хасан Хашим5, Амани Хусейн6, Эмад
Юсиф1*
1 Кафедра химии, научный колледж, Университет Аль-Нахрейн, Багдад, Ирак 2Кафедра химической промышленности, Технологический институт Багдада, Средний технический
университет, Багдад, Ирак 3Кафедра наук об окружающей среде, Колледж энергетики и наук об окружающей среде, Научный
университет Аль-Карха, Багдад, Ирак 4Кафедра химии, научный колледж, Университет Объединенных Арабских Эмиратов, Аль -Айн,
Объединенные Арабские Эмираты 5 Факультет физики, Научный колледж, Университет Аль-Нахрейн, Багдад, Ирак 6Отдел исследования полимеров, Научный колледж, Университет Мустансирия, Багдад, Ирак * e-mail: [email protected] [email protected]
Абстракт: Поливинилхлорид (ПВХ) находит разнообразное применение, существенно влияющее на нашу повседневную жизнь, и промышленно синтезируется в различных формах. Однако ПВХ подвергается фоторазложению, образуя токсичные побочные продукты, вредные как для окружающей среды, так и для здоровья человека, тем самым сокращая срок его службы. Чтобы решить эту проблему, в настоящей работе изучено применение металлокомплексов в качестве потенциальных фотостабилизаторов для смягчения фоторазложения ПВХ. Это исследование углубляется в эффективность недавно разработанных комплексов металлов в смягчении фотодеградации, изучая такие параметры, как ослабление молекулярной массы, образование алкен -нагруженных и карбонильных фрагментов, а также изменения морфологии поверхности листов ПВХ, подвергнутых облучению. Результаты исследований показывают, что эти инновационные металлокомплексы демонстрируют эффективность в уменьшении фотодеградации поливинилхлорида, тем самым представляя многообещающий путь к продлению его функциональной долговечности.
Ключевые слова: поливинилхлорид; металлокомплексы; фотодеградация; морфология поверхности; снижение молекулярной массыКлючевые слова: поливинилхлорид; металлокомплексы; фотодеградация; морфология поверхности; снижение молекулярной массы
