Polymer Degradation and Stability
, Pages 110-119
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In this study, new multifunctional organic-inorganic pigments were synthesized by the complexation of carboxlic azo dyes (D1, D2) with aluminum-magnesium hydroxycarbonate (LH) and were applied as colorants in ethylene-norbornene copolymer (EN). The structures of the hybrid pigments were analyzed by X-ray diffraction (XRD), secondary ion mass spectrometry (TOF-SIMS), thermogravimetric analysis (TGA) and scanning electron microscopy (SEM). X-ray diffraction revealed that the hybrid pigments had developed new crystalline structures and showed the presence of additional peaks on their diffraction patterns. Moreover, TOF-SIMS confirmed that the modification had been successful, with the formation of dye-metal complexes embedded in the LH structure. The EN composites with hybrid pigments were subjected to accelerated UV aging. Alterations were monitored by Fourier transform infrared spectroscopy (FT-IR), spectrophotometry, differential scanning calorimetry (DSC) and mechanical tests. It was found that the EN composites containing hybrid pigments showed approximately 4 times higher tensile strength than both EN and an EN sample with unmodified LH under 250 h of UV irradiation. Adding 2 wt% of the multifunctional hybrid pigments to EN copolymer significantly enhanced the aging resistance and thermal stability of the resulting composites.
Polymers are used in an increasingly wide range of applications, where long-term maintenance is required in hostile environments. However, many polymers are difficult to process without additives: some vital properties need to be enhanced, while undesirable properties need to be minimized or even eliminated to meet different requirements. Polymer additives may affect the aging process in final materials, acting as a stabilizer or prodegradant under high temperatures or in outdoor conditions [, , , ]. It is known that anatase form of titanium dioxide (TiO2) is markedly photosensitive in degrading polymers . Very recently, it has been also reported that the addition of clays such as aluminum-magnesium hydroxycarbonate to some composites accelerates their photo-degradation rate [6,7]. Organic and inorganic pigments are mainly applied in polymer composites to provide color. However, they can also have a great influence on the photo and thermostability of the final products [8,9]. For example, by absorbing and/or scattering UV, pigments can have a marked protective effect [10,11].
There is currently great interest in organic-inorganic pigments, which can combine the advantages of both organic materials (such as versatility of color) and inorganic materials (high resistance to chemicals and light) . Conventionally, hybrid pigments are obtained by precipitating dyes onto inorganic substrates, such as alumina or calcium carbonate, forming organic-inorganic pigments (lakes) [13,14]. The precipitation of dyes onto inorganic matrices via covalent and/or coordination bonds enables metal dye complexes to be obtained with low solubility, good color strength, and enhanced performance in applications [15,16]. Many studies have investigated the intercalation of various dyes into layered double hydroxide structures, reporting improved UV, oxidative and thermal stability [, , ]. It has also been observed that by modifying layered double hydroxide, its catalytic effect on the rate of polymer photodegradation can be changed, and that azo-dye modified structure may act as a UV-shield in PP composites . However, the intercalation of dye-containing anions into the interlayer space of hydrotalcites is time-consuming and requires an inert atmosphere [, , ]. Therefore, it is still necessary to find new, simple to produce organic-inorganic hybrid pigments with high resistance to dissolution and good thermal/photo stability.
The present study proposes a new precipitation method for preparing hybrid pigments based on azo dyes (D1, D2) and aluminum-magnesium hydroxycarbonate (LH) with Mg/Al weight ratio 30:70. The selected LH matrix offers a promising carrier for the synthesis of organic-inorganic pigments, due to its relatively large surface area and interesting properties as a polymer additive (color stability, strength, and flame retardancy). The structural characteristics of the hybrid pigments were studied using time-of-flight secondary ion mass spectrometry (TOF-SIMS) and X-ray diffraction analysis (XRD), as well as scanning electron microscopy (SEM). Solvent resistance and thermal stability were tested to assess the applicative properties of the pigments. The prepared EN composites were subjected to accelerated UV aging and further characterized via FT-IR spectroscopy, differential scanning calorimetry (DSC), tensile testing, and spectrophotometric measurements.
Ethylene-norbornene random copolymer (EN) with 40 wt% bound norbornene content was supplied by TOPAS Advanced Polymers (Germany). Aluminum-magnesium hydroxycarbonate with a Mg:Al weight ratio of 30:70 (specific surface area 250 m2/g, loose bulk density 350–550 g/l, pore volume 0.5 ml/g) was purchased from Sasol GmbH (Germany). Analytical grade organic solvents – toluene, acetone, ethanol, and butyl acetate – were purchased from Sigma-Aldrich (Germany). The azo dyes (Fig.1) employed as an
The interactions between the organic and inorganic parts of the prepared hybrid pigments were observed by secondary ion mass spectrometry (TOF-SIMS). The TOF-SIMS spectra were recorded using a TOF-SIMS IV mass spectrometer (IONTOF GmbH, Germany), equipped with a Bi liquid metal ion gun and a high mass resolution time of flight mass analyzer. The analyzed area of the sample was irradiated with pulses of 25 keV Bi3+ ions at a repetition rate of 10 kHz and with an average ion current of 0.4 pA.
X-ray diffraction analysis (XRD) and scanning electron microscopy (SEM) of pigment powders
The X-ray diffraction technique was used to study the crystal structure of the newly synthesized hybrid pigments. Fig.2a shows the powder X-ray diffraction pattern of aluminum-magnesium hydroxycarbonate. The peaks assigned to the planes (003), (006), (009), (110), and (113) are characteristic for hydrotalcite materials with a layered structure . The reflection assigned to (003) plane could be used to calculate the basal spacing d between the layers. The peak which appears at 2θ = 11.78°
In this study, new hybrid pigments were prepared by the complexation of azo dyes (D1, D2) with aluminum-magnesium hydroxycarbonate (LH). The incorporation of azo dyes into the LH matrix contributed to the formation of organic-inorganic crystal structures and was most likely caused by dye-magnesium interactions, as confirmed by TOF-SIMS. The obtained organic-inorganic colorants demonstrated higher thermal stability than pristine LH and significantly better resistance to dissolution in organic
This work was supported by the National Science Center of Poland (Miniatura no. 2017/01/X/ST5/01105).
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New natural organic–inorganic pH indicators: Synthesis and characterization of pro-ecological hybrid pigments based on anthraquinone dyes and mineral supports
2022, Journal of Industrial and Engineering Chemistry
Citation Excerpt :
These challenges have recently been overcome by the new concept of stabilizing organic dyes on inorganic supports (such as halloysite or montmorillonite), usually by the adsorption or intercalation of the organic dye onto the inorganic carrier. This can result in the formation of organic–inorganic pigments with improved thermal, chemical, and light stability [11–15]. Organic–inorganic pigments have become the most popular group of modern colorants with improved physico-chemical properties.
We present a strategy that leads to the formation of high-performance hybrid pigments made from natural anthraquinone chromophores (alizarin, purpurin) and mineral supports (palygorskite (PAL), sepiolite (SEP), and hydroxyapatite (HAP)). Thanks to the mineral filler form features and the synergy between the organic and inorganic components, the as-prepared hybrid pigments showed excellent thermal and chemical stability. The natural pigments exhibited strong pH-sensing activity, changing their color upon exposure to HCl and/or NH3 vapors. The PAL-based pigments were found to be the most effective pH indicators, showing pronounced color changes after 10min of exposure to HCl (ΔE for PAL/A was 7.4). ToF-SIMS, 13C NMR and XPS techniques revealed interactions between the organic dyes and metal ions present in the minerals. XPS spectroscopy was also used to examine the alterations in the structure of the hybrid colorants following exposure to acid vapors. The proposed pH sensors were successfully applied to elastomer and thermoplastic elastomer matrices. The purpurin-based hybrid pigments exhibited significantly reduced migration from the polymer (about six times lower concentration in ethanol after 14days). The results of this study pave a new way for the design, development, and application of advanced hybrid colorants with pH-sensing activity and improved stability.
Impact of organic-inorganic color additive on the properties of ethylene-norbornene copolymer
2020, Polymer Testing
Citation Excerpt :
In a previous work, we used mono and dicarboxylic azo dyes modified with aluminum-magnesium hydoxycarbonates to produce organic-inorganic pigments , which were found to improve the permeability and flame resistance of elastomer composites cured with different crosslinking systems. In other research, exposure tests showed a significant improvement in the photo-stability of ethylene-norbornene (EN) composites containing organic-inorganic pigments compared to an EN/dye sample . The present paper reports the modification of aluminum-magnesium hydoxycarbonate with azo dye containing a carbonyl group and sulfur in its structure.
In this study, we developed a new organic-inorganic pigment (LP) by precipitation of dye molecules onto aluminum-magnesium hydroxide (LH). The morphology and physico-chemical properties of the pigment were characterized by X-ray diffraction analysis (XRD), secondary ion mass spectrometry (TOF-SIMS), 27-Al solid-state nuclear magnetic resonance (NMR) spectroscopy, scanning electron microscopy (SEM) and thermogravimetric analysis (TGA). The incorporation of the azo dye into the LH host caused an increase in the interlayer distances of the LP from 0.751 to 0.758nm. The LP pigment also showed better thermal- and photo-stability than the pristine azo chromophore. The novel organic-inorganic additive was next applied as a filler at different concentrations (2 phr, 5 phr, 10 phr) to obtain colorful ethylene-norbornene (EN) films. The morphological, mechanical and flame-retardant properties of the composites were determined by XRD, SEM, dynamic-mechanical analysis (DMA) and cone calorimetry tests (CCT). The EN films containing the LH/Azo dye demonstrated improved mechanical, barrier and flame-retardant properties. Compared to the neat EN copolymer and EN/LH composite, the EN/LP sample was found to be the most resistant to UV aging, as confirmed by FTIR and mechanical analysis.
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