Morphological and thermal properties of the biodegradable graft copolymer lldpe-g-ma/gel composites Текст научной статьи по специальности «Техника и технологии»

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d ) https://dx.doi.org/10.36522/2181-9637-2023-4-4 UDC: 678.742.23+665.931.7(045)(575.1)

MORPHOLOGICAL AND THERMAL PROPERTIES OF BIODEGRADABLE GRAFT COPOLYMER LLDPE-G-MA/GEL COMPOSITES

Normurodov Nurbek Fayzullo ugli,

PhD student, е-mail: nurbeknormuradov27@gmail.com;

Berdinazarov Kadirbek Nuridin ugli,

PhD student;

Khakberdiev Elshod Olmosovich,

Doctor of Philosophy in Technical Sciences (PhD), Junior Researcher;

Dusiyorov Nizomiddin Zokir ugli,

Junior Researcher;

Ashurov Nigmat Rustamovich,

Doctor of Technical Science, Professor, Head of Laboratory

Institute of Chemistry and Physics of Polymers of the Academy of Sciences

of the Republic of Uzbekistan

Introduction

Mixture of polyolefins with natural thermoplastics is ofgreat interest not only from the scientific point of view, but also because of the possibility of its practical application. Polymers are blended to produce polymer materials with new and better properties and to expand the range of polymer materials.

Uncontrolled development of morphology at the stage of forming of biodegradable compositions based on synthetic and natural polymers restrains achieving satisfactory physical, mechanical and operational characteristics. Several studies have reported successful preparation of PE/gelatin blends using various techniques, such as solution casting, melt blending, and electrospinning. These studies showed that adding of gelatin can improve mechanical, thermal, and barrier properties of the blends (Normurodov, Berdinazarov, Khakberdiev, Dusiyorov, & Ashurov, 2022), (Normurodov, Berdinazarov,

Abstract. In this work, a biodegradable graft copolymer based on linear low density polyethylene grafted maleic anhydride and gelatin (LLDPE-g-MA/Gel) was formed by reactive mixing of functionalized polyethylene with gelatin to achieve finely dispersed blend morphology. Using a selection of components of the mixture, we'd studied its morphology and thermal properties. It was found that thermal stability (initial temperature) of the composition decreases as the amount of gelatin increases due to degradation of gelatin. In the temperature range of 400-500 °C, the maximum rate of destruction of the graft copolymer increases significantly with higher gelatin content. Samples having identical composition were selected using a Brabender plastograph and a mechanical mixer; and when taken at different rates, the morphological structure of the samples was determined to depend on their mixing rate. The morphological structure was found to show that increased speed leads to effective reaction of two components and crushing of particles into smaller ones.

Keywords: TGA, DSC, Biodegradation, gelatin, glycerin, polyethylene, maleic anhydride.

BIOLOGIK PARCHALANUVCHI PAYVAND SOPOLIMER LLDPE-G-MA/GEL KOMPOZITLARNING MORFOLOGIK VA TERMIK XUSUSIYATLARI

Normurodov Nurbek Fayzullo o'g'li,

tayanch doktorant;

Berdinazarov Qodirbek Nuridin o'g'li,

tayanch doktorant;

Haqberdiyev Elshod Olmosovich,

texnikа fanlari bo'yicha falsafa doktori (PhD), kichik ilmiy xodim;

Dusiyorov Nizomiddin Zokir o'g'li,

kichik ilmiy xodim

Ashurov Nigmat Rustamovich,

texnika fanlari doktori, professor, laboratoriya mudiri

O'zbekiston Respublikasi Fanlar akademiyasi Polimerlar kimyosi va fizikasi instituti

Annotatsiya. Ushbu maqolada nozik disperslan-gan aralashma morfologiyasiga erishish uchun funk-sionallashtirilgan polietilenni jelatin bilan reaktiv ara-lashtirishda chiziqli past zichlikli polietilen payvand-langan maleik angidrid va jelatin (LLDPE-g-MA/Gel) asosida bioparchalanuvchi payvand sopolimeri hosil qilish jarayoni yoritilgan. Aralashmaning tarkibiy qism-larini tanlash yordamida uning morfologiyasi va termal xususiyatlari o'rganildi. Jelatin degradatsiyasi tufayli uning miqdori oshgani sayin kompozitsiyaning termal barqarorligi (dastlabki harorat) pasayishi aniqlandi. 400-500°C harorat oralig'ida jelatin miqdori ortishi bilan payvand sopolimerining parchalanish tezligi sezi-larli darajada oshadi. Xuddi shu tarkibdagi namunalar Brabender plastografi va mexanik aralashtirgich yor-damida olindi va namunalarning morfologik tuzilishi ularning aralashtirish tezligiga qarab aniqlandi. Morfologik tuzilishiga ko'ra, tezlik ortib borishi ikki kom-ponentning samarali reaksiyaga kirishishi va zarralar-ning kichrayishiga olib keladi.

Kalit so'zlar: TGA, DSK, biologik parchalanish, jelatin, glitserin, polietilen, malein angidrid.

МОРФОЛОГИЧЕСКИЕ И ТЕРМИЧЕСКИЕ СВОЙСТВА БИОРАЗЛАГАЕМЫХ

ПРИВИТЫХ СОПОЛИМЕРОВ LLDPE-G-MA/GEL КОМПОЗИТОВ

Нормуродов Нурбек Файзулло угли,

докторант;

Бердиназаров Кодирбек Нуридин угли,

докторант;

Haqberdiyev, Dusiyorov, & Ashurov, 2022), (Wollerdorfer, & Bader, 1998), (Guo, He, Yang, Xue, Zuo, Yu, & Rafailovich, 2016). Blending can improve a wide variety of polymer properties. However, while polymer blending is attractive for producing new materials, most polymer blends are incompatible. This is the reason for difficulties faced in treatment processes and worsening of performance properties of such polymer mixtures (Rustgi & Rustgi, 1998), (Nayak, 1999).

Packaging industry needs biodegradable materials. Traditional synthetic polymers, in particular polyolefins, despite a good combination of production technology, the possibility of varying physical and mechanical characteristics and prices, pose significant problems for the environment. To address this issue, researchers have investigated the use of biodegradable additives in view of improving biodegradability of PE while maintaining its properties. (Tian & Bilal, 2020), (Meena, et al., 2017), (Bastioli, 2001). Analytical review indicates that solution to this problem is seen in the use of biopolymers, or their combination with synthetic polymers.

From this point of view, interest in creation of blends of gelatin with synthetic polymers continues unabated (Sarker, Dey, & Khan, 2011), (Kaur, et al., 2008). At the same time, it was noted that normal mixing of gelatin with polyolefin at various ratios produces very low biodegradability rates (up to 10%), optimizing the morphology of the blend by transferring gelatin to its thermoplastic state can slightly increase this indicator.

Given the expanding environmental pollution crisis, biodegradable polymers have drawn great research attention in the academy and industry in the past two decades. These environmentally benign polymers have been recognized as promising materials for replacing traditional polymers, because their biodegradability can reduce waste pollution. Biopolymers, including gelatin, chitosan, and starch, have attracted great attention owing to their biodegradability, biocompatibility, and renewability. Gelatin, in particular, a

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protein-based biopolymer derived from animal collagen is broadly used in various applications, including food, pharmaceuticals, and cosmetics (Lim, Auras, & Rubino, 2008), (Behera, Sivanjineyulu, Chang, & Chiu, 2018). Biodegradable polymer-based blends were produced to enhance various properties of original polymer components notably (Raquez, Ramani, & Dubois, 2008), (Visakh & Nazarenko, 2015). Crystallization rate and crystallinity of crystalline polymers play important role in resultant properties and final applications. An enormous diversity of morphologies and super-molecular structure can be achieved by varying crystallization conditions of crystallizable polymers (Vilay, Mariatti, Ahmad, Pasomsouk, & Todo, 2009), (Kalb & Pennings, 1980), (Harada, Ohya, Iida, Hayashi, Hirano, & Fukuda, 2007), (Mileva, Tranchida, & Gahleitner, 2018), (Li & Yan, 2011), (Felder, et al., 2020).

As a result ofthisresearch, we haveobtained LLDPE-g-MA/Gel copolymers based on maleic anhydride (MA) grafted polyethylene (PE), (LLDPE-g-MA) and gelatin (Gel). The work was focused on investigating and comparing crystallinity and morphological structures, thermal stability, and hydrolytic degradation of neat PE, LLDPE-g-MA (5%) and LLDPE-g-MA/Gel composites and components.

Materials and methodology

Materials

Research and experiments were carried out by the authors of the article in the laboratory of nanostructured polymer composite materials at the Institute of Polymer Chemistry and Physics under the scientific project aimed at the fundamental goal of "Nanocomposite polymer based on polyolefins - polymer blends materials produced in Uzbekistan" in 2022-2023.

Materials used: Linear low-density polyethylene (LLDPE) grade F-0320, d = 0.920 g/cm3, MFI = 2.5 g/10 min (at a load of 2.16 kg). Producer - Shurtan Gas Chemical Complex of the Republic of Uzbekistan; Edible gelatin (GEL) grade P - 200 (GOST 11293 -2019). Producer JSC "MOGELIT", Belarus; Maleic anhydride (MA) C4H2O3, analytical

Хакбердиев Элшод Олмосович,

доктор философии по техническим наукам (PhD), младший научный сотрудник;

Дусиёров Низомиддин Зокир угли,

младший научный сотрудник;

Ашуров Нигмат Рустамович,

доктор технических наук, профессор, заведующий лабораторией

Институт химии и физики полимеров Академии наук Республики Узбекистан

Аннотации. В этой работе биоразлагае-мый привитой сополимер на основе линейного полиэтилена низкой плотности с привитым малеиновым ангидридом и желатином (LLDPE-g-MA/Gel) был получен путем реактивного смешивания функционализированного полиэтилена с желатином для достижения мелкодисперсной морфологии смеси. С помощью подбора компонентов смеси изучены ее морфология и термогравиметрические свойства. Установлено, что термостабильность (начальная температура) композиции снижается по мере увеличения количества желатина за счет его деградации. В интервале температур 400-500 °С с увеличением содержания желатина максимальная скорость разрушения привитого сополимера значительно возрастает. Образцы одинакового состава отбирали с помощью пластографа Брабендера, механической мешалки, определяли морфологическую структуру образцов в зависимости от скорости их перемешивания. По морфологической структуре было установлено, что увеличение скорости приводит к эффективной реакции двух компонентов и дроблению частиц на более мелкие.

Ключевые слова: ТГА, ДСК, биодеградация, желатин, глицерин, полиэтилен, малеиновый ангидрид.

grade, colorless rhombic crystals, Mr = 98.06 g/mol, was distilled at Tbp = 84.0 °C/14 mm Hg, Tm = 60 °C, p60 = 1.3140 g/cm3.

Preparing the thermoplastic gelatin

To dissolve gelatin granules and make them thermoplastic, we put glycerin into the distilled water and stirred until reaching the same mixture, then added gelatin to the resulting mixture and stirred again, then heated it in an oven at 80 °C for two hours.

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Functionalization

Functionalization of LLDPE with maleic anhydride (LLDPE-g-MA) was carried out on a Brabender plastograph (Plasticorder Brabender OHGDUISBURG Germany), with a cam speed of 98 rpm and at a temperature of 180 ± 5 °C (Ashurov, Sadikov, Khakberdiev, Berdinazarov, Normurodov, 2020). The concentration of maleic anhydride in the weld is 5.0% by weight.

Polymer blends based on LLDPE-g-MA and gelatin were obtained on a Brabender plastograph, for 20 min, at 50 rpm and 180 ±5°C by adding plasticized gelatin to the LLDPE-g-MA melt.

DSC and TGA measurements Thermal analyses DSC and TGA of polymer blends was carried out in a dynamic mode on a LINSEIS THERMAL ANALYSIS PT1600 [thermogravimetric analysis (TGA)] instrument (in air atmosphere) in the range between room temperature and 1000°C, guided by the requirements established by the ASTM E 1131 standard. The heating rate was 10 °C/min, the sample weight for analysis was from 2 to 100 mg.

Atomic force microscope (AFM) The morphology of polymer mixtures was studied using atomic force (scanning probe microscope Agilent 5500) microscopy at the

room temperature. We used silicon cantilevers with stiffness of 9.5 N/m and a frequency of 145 kHz. The maximum scanning area on AFM along X, Y is 15 x 15 [im2, along Z it is 1 [im. Research findings TGA and DSC measurements Thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) are commonly used techniques to investigate thermal properties of materials. Findings from the measurements can provide valuable information on thermal stability, decomposition behavior, and phase transitions of the materials in question.

The statement in the text suggests that the TGA measurements have revealed presence of reaction products in the mixtures and initial components under investigation. Changes in the thermogravimetric characteristics, i.e. initial degradation temperature (T.) and the temperature of the maximum degradation rate (T ), indicate to forming of new compounds or degradation of the original components.

Table 1 provides a summary of the T, and T values for various compositions of

max r

mixtures and initial components. These values can be used to compare thermal stability of different materials as well as to assess the effect of mixing on thermal properties of the omposite materials.

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b)

Fig. 1. Thermogravimetric curves (a) and the first derivative of the TGA curves (b) of the film sample

Thermal characteristics of LLDPE-g-MA/gelatin blends

Table 1

Temperature according to the loss of mass is °C

№ Sample name & component ratio (wt%) Initial degradation temperature Ti, °C Maximum thermal decomposition rates (T ), °C » max" Crystallinity degree, %

Stage I Stage II Stage III

1 LLDPE 186 19.85

2 LLDPE-g-MA (5%) 242 18.15

3 LLDPE-g-MA/GEL 70/30 233 100-200°C m(mg) < 10% 275-400 °C 10 < m(mg) < 50% 400-500 °C m(mg) > 50% 14.85

4 LLDPE-g-MA/GEL 60/40 223 13.32

5 LLDPE-g-MA/GEL 50/50 190 12.02

6 LLDPE-g-MA/GEL 40/60 201 10.4

7 GELATIN 97 -

Thermal decomposition of the LLDPE-g-MA/gelatin mixture on TGA curves comprises three sequential stages. Stage I in the temperature range of 100-200 °C is caused by the loss of absorbed and bound water molecules (weight loss less than 10% weight). Stage II, observed within 275-400 °C (weight loss in the range of 10-50 wt%), corresponds to breaking of peptide bonds in the gelatin macro chain (Moreno, Diaz, Atares, & Chiralt, 2016). Temperatures corresponding to the

maximum rate of thermal decomposition of the gelatinous phase are within 250280 °C. Partial contribution to the weight loss of the composition in this temperature range is also made by the onset of LLDPE-g-MA dehydrogenation, the maximum rate of thermal decomposition (Stage III) which falls at 450 oC. The position of this peak does not practically depend on the content of gelatin in the composition; as the content of gelatin increases, it slightly shifts towards higher

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temperatures (up to 7 oC). Summarizing the above TGA data, it can be noted that forming of the graft copolymer LLDPE-g-MA/gelatin leads to a decrease in thermal stability in terms of T, by 10-40 °C, depending on the content of gelatin 30-60 wt%, respectively, while the maximum rate of thermal decomposition of the graft copolymer (Stage III) rise in the biopolymer content increases significantly (from -0.14 to -0.23 mg/K) due to degradation of grafted gelatin.

Atomic force microscope (AFM)

The use of atomic force microscopy (AFM) in the study of the morphology of dispersed phase particles in polyethylene gelatin composites is a valuable technique as it enables high-resolution imaging of the surface topography that can provide information on the size, shape, and distribution of the particles.

The findings presented in Figure 3 suggest that the mixing speed has a significant effect on the size and shape of the dispersed phase particles. Specifically, increasing the mixing speed from 50 to 150

rpm leads to a reduction in particles' size and a change in their shape. This suggests that the use of higher mixing speeds may be beneficial in achieving a more uniform distribution of the dispersed phase particles in the composite material, that can ultimately lead to improved physical and mechanical properties.

Overall, the use of AFM jointly with varying speeds of mixing provides valuable insights into the morphology of composite materials and can help in the development of better processing methods for these materials.

In order to prevent coalescence of particles of the dispersed phase of gelatin in polyethylene and ensure a uniform morphological distribution, the samples were mixed at three different speeds and studied under atomic force microscopy (AFM). The speeds varied from 50 rpm, to 100 and 150 rpm (fig. 3). The phase analysis of the size and distribution of the dispersed phase particles shows that the dispersed phase particles become smaller in size and have different shapes when the speed rises.

50 rpm 100 rpm 150 rpm

Fig. 3. Atomic stress microscope images of samples taken at 50, 100 and 150 rpm

AFM studies show that in the structure of the drawn samples, the dispersed phase particles of the second component increased in velocity, and distribution improved with less coalescence. Thus, microscopic studies have shown that the obtained polymer mixtures have a structural morphology that helps to improve physical and mechanical properties of resulted materials.

Conclusions

Grafting of thermoplastic gelatin to maleated polyethylene promotes formation of homogeneous compositions with a finer dispersion of the gelatin phase in the polyethylene matrix. Three stages of thermal decomposition of the LLDPE-g-MA/gelatin composition associated with the presence of water molecules, degradation of the

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gelatin and polyethylene phases, have been identified.

The presence of gelatin shifts significantly the onset temperature of decomposition towards low temperatures (from 242 to 2010C), while the temperature range of degradation of the polyethylene matrix does not undergo visible changes. The maximum rate of degradation of the graft copolymer in the temperature range of 400-500 0C with an increase in the content of gelatin grows noticeably up from -0.14 to -0.23 mg/K. microscopic studies showed that the

resulted polymer mixtures have a structural morphology that helps to improve physical-mechanical properties of the obtained materials.

Overall, the findings from this study demonstratea potentialofusingreactivemixing to achieve a finely dispersed blend morphology in biodegradable copolymers. Observations on the effects of gelatin content and mixing speed on thermal and morphological properties of the copolymer provide valuable insights into the development of better processing methods for these materials.

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Reviewer: Karabaeva M.A., Doctor of Philosophy in physical and mathematical Sciences (PhD), Associate Professor, Faculty of Physics, National University of Uzbekistan named after Mirzo Ulugbek.