ABSTRACT
The effects of three different mixers, two different feeding orders, and nanoclay content on the structure development and rheological properties of PE/nanoclay nanocomposite samples were investigated. Fractional Zener and Carreau–Yasuda models were applied to discuss the melt linear viscoelastic properties of the samples. Moreover, scaling law for fractal networks was used to quantify the clay dispersion, which depends on the PE matrix structure. A better dispersion and higher melt intercalation of nanoclay particles were obtained by simultaneous feeding compared to compatibilizer/nanoclay masterbatch feeding. A twin-screw extruder (Brabender DSE 25 model) showed a greater potential for melt intercalation of PE/nanoclay as compared to internal mixers (Brabender W50 and Haake Rheomix 3000 batch mixers). Comparing the thermal analysis of PE, PE/PE-g-MA and PE/nanoclay samples by the DSC technique showed an opposite effect for the compatibilizer versus the nanoclay on the crystallization behavior of PE. PE/nanoclay cast film samples were produced at three different draw ratios. The X-ray diffraction structural analysis in conjunction with the melt linear viscoelastic measurements confirmed that the PE/nanoclay cast film produced at a higher draw ratio had more effective melt intercalation. The tensile test showed that the machine direction modulus and yield strength of both PE and PE/nanoclay cast film samples reduced with an increase of the draw ratio. Polyolefins J (2018) 5:47-58
Keywords
Polyethylene, nanocomposite, film, rheology, tensile test
INTRODUCTION
Due to excellent processability, high chemical resistance, safety in contact with food products, desirable physical properties, and low cost, PE has received the most attention in different applications ranging from the packaging industry to greenhouse covering, geomembrane, and pipe applications [1-3]. However, some limitations such as poor rigidity and low gas barrier properties have restricted its application in some fields. Research on polymer nanocomposites with very low clay content is an area of research that has seen a huge interest over the last two decades as a result of significant enhancement in properties such as stiffness and strength, flame retardancy, barriers, and thermal stability [4-9]. All these properties open up interesting prospects for use of these materials in a wide variety of applications [10-13]. Due to the wide availability of the melt intercalation equipment, it is a common method in industrial practice for preparing thermoplastic nanocomposites. Some studies have shown that in this method the extent of clay intercalation is influenced by equipment type. The internal mixers and twin-screw extruders are the pieces of equipment commonly used for producing nanocomposites [14, 15].
A high intercalation level requires favorable polymer–clay interactions as well as optimum processing conditions. It is usually a difficult task to produce PE nanocomposites with a desirable structure, due to the very weak interactions between the polyethylene molecules and the polar surface of clays. Chungui Zhao et al. showed that the partially exfoliated structure formed in PE/nanoclay nanocomposites due to incorporation of modified montmorillonite clay was obtained due to the presence of a reactive intercalating agent, while only conventional microcomposites were obtained with adding the common alkylammonium intercalated clay [16]. Modified polymers having polar groups, also called compatibilizers, can be introduced into nanocomposite formulations to enhance the extent of intercalation [17, 18]. Pegoretti et al. showed that the presence of a PE-g-MA compatibilizer in PE/nanoclay samples increased the nanoclay interlayer d-spacing. They also demonstrated that the extent of melt intercalation increased as the PE matrix melt viscosity decreased (higher MFR) [19]. Durmus et al. explained that in PE/nanoclay nanocomposites a better dispersion was achieved with the incorporation of a maleic anhydride grafted polyethylene (PE-g-MA) compatibilizer than that obtained with the incorporation of an oxidized PE (OxPE) compatibilizer [20]. Sanchez-Valdes et al. showed that a more effective intercalation and dispersion condition could be obtained in the preparation of compatibilized PE/nanoclay nanocomposites performed by two-step twin-screw melt mixing compared to one-step melt mixing [21].
In polymer/nanoclay nanocomposites, the extent of intercalation and degree of dispersion of clay can be evaluated by X-ray diffraction (XRD) along with transmission electron microscopy (TEM). Although XRD offers a convenient method to determine the interlayer spacing in the original clay layers and intercalated structure, a little information can be obtained about the spatial distribution of clay layers and/or any disordered structure. In contrast to XRD, TEM provides very useful information about the dispersion state of clay particles in a wide range of length scales, but it is a time consuming and expensive technique.
[22, 23]. It is well known that the rheological properties of multiphase systems including particulate suspensions are very sensitive to structure, size, shape, and surface characteristics of dispersed phase. Thus, the rheology can be employed as a powerful method in complementary to conventional methods such as XRD and TEM to study structure of polymer clay nanocomposites [24]. Moreover, the rheological studies provide valuable information about the processability of these materials in melt processing units such as extrusion and film casing process [25, 26]. Film is the largest market segment for polyethylene (PE). Improvements in properties of the PE films by incorporation of clay nanoparticles can promote current applications and even more advanced applications like the horticultural product, electronic and pharmaceutical packaging. On the other, the ability of polyethylene to be converted into film depends on its melt strength or equivalent rheological properties, like the elongational viscosity and viscoelastic behavior that can be affected by the incorporation of clay.Some literature shows the effect of film processing parameters such as drawdown ratio and blows up ratio on mechanical and gas barrier properties of polyethylene/nanoclay nanocomposite blown films [8, 27-29]. However, there is no report on the effect of processing parameters on structure development and mechanical properties of PE/clay nanocomposite cast films. The aim of this work was studying the effects of mixer type, clay content, feeding order, and draw ratio on the structure development, rheological, thermal, and mechanical properties of PE/nanoclay nanocomposites and PE/nanoclay nanocomposite cast films.
CONCLUSION
Three types of mixing machines including a Brabender twin-screw extruder, a Haake internal mixer (with a 350 mL capacity), and a Brabender internal mixer (with a 60 mL capacity) were used to prepare LLDPE/nanoclay samples contacting 4 wt.% cloisite. It was shown that the sample prepared by the twin-screw mixer exhibited a pronounced low-frequency nonterminal storage modulus and viscosity upturn, whose values were found to be greater than those of samples prepared by the internal mixers. This could be attributed to the greater potential of the twin-screw extruder in melt intercalation of nanoclay existed in comparison with the internal mixers. From the melt linear viscoelastic results obtained for the samples prepared by the simultaneous feeding and the compatibilizer/nanoclay masterbatch feeding, it was observed that the dispersion and intercalation of nanoclay in the sample prepared by masterbach feeding was worse due to the trapping of more nanoclay particles in the compatibilizer and formation of a weaker 3D-network structure. Fractal scaling model showed that a better dispersion of nanoclay particles was achieved in the LLDPE than that in the LDPE in accordance with the XRD and TEM results. The results of linear melt viscoelastic measurement performed on the LLDPE/nanoclay cast films showed an increase of low-frequency storage modulus with increasing draw ratio as a result of better melt intercalation. It showed that the hindered motions of molecules led to a decrease in the growth rate of nucleates in the LLDPE/LL-g-MA/nanoclay sample containing 4wt% nanoclay, resulting in a decrease of Tc. The tensile test showed that the incorporation of nanoclay into the cast films increased the machine direction modulus and yield strength, nevertheless, decreased the elongation-at-break. Moreover, in both the filled and unfilled cast films, the increase of draw ratio decreased their mechanical properties.
About KSRA
The Kavian Scientific Research Association (KSRA) is a non-profit research organization to provide research / educational services in December 2013. The members of the community had formed a virtual group on the Viber social network. The core of the Kavian Scientific Association was formed with these members as founders. These individuals, led by Professor Siavosh Kaviani, decided to launch a scientific / research association with an emphasis on education.
KSRA research association, as a non-profit research firm, is committed to providing research services in the field of knowledge. The main beneficiaries of this association are public or private knowledge-based companies, students, researchers, researchers, professors, universities, and industrial and semi-industrial centers around the world.
Our main services Based on Education for all Spectrum people in the world. We want to make an integration between researches and educations. We believe education is the main right of Human beings. So our services should be concentrated on inclusive education.
The KSRA team partners with local under-served communities around the world to improve the access to and quality of knowledge based on education, amplify and augment learning programs where they exist, and create new opportunities for e-learning where traditional education systems are lacking or non-existent.
FULL Paper PDF file:
Rheological, thermal and tensile properties of PE/nanoclay nanocomposites and PE/nanoclay nanocomposite cast films
Bibliography
author
Year
2017
Title
Rheological, thermal and tensile properties of PE/nanoclay nanocomposites and PE/nanoclay nanocomposite cast films
Publish in
Polyolefins Journal
Doi
PDF reference and original file: Click here
Nasim Gazerani was born in 1983 in Arak. She holds a Master's degree in Software Engineering from UM University of Malaysia.
Professor Siavosh Kaviani was born in 1961 in Tehran. He had a professorship. He holds a Ph.D. in Software Engineering from the QL University of Software Development Methodology and an honorary Ph.D. from the University of Chelsea.
Somayeh Nosrati was born in 1982 in Tehran. She holds a Master's degree in artificial intelligence from Khatam University of Tehran.
