Advanced Materials Research Vols. 488-489 (2012) pp 1525-1529 Online available since 2012/Mar/15 at www.scientific.net © (2012) Trans Tech Publications, Switzerland doi:10.4028/www.scientific.net/AMR.488-489.1525
Preparation of LLDPE/Modified Silica Nanoparticle with Triethoxyvinylsilane Film for Microwaveable Packaging Arjaree Pradittham1,a, Supapen Trejitwattanaku1,b, Titima Sramanee1,c, Sarinthip Thanakkasaranee1,d Duangduen Atong 2,e and Chiravoot Pechyen1,3,f 1
Department of Packaging and Materials Technology ,Faculty of Argo-Industry ,Kasetsart University ,Bangkok 10900, Thailand
2
National Metal and Materials Technology Center, 114 Thailand Science Park, Pathumthani 12120, Thailand
3
Center for Advanced Studies in Agriculture and Food ,KU Institute for Advanced Studies ,Kasetsart University ,Bangkok 10900 ,Thailand (CASAF, NRU-KU, Thailand) a
[email protected], b
[email protected], c
[email protected], d
[email protected],
[email protected],
[email protected]
Keywords: Silica nanoparticle, Triethoxyvinylsilane, LLDPE, Microwaveable packaging
Abstract. Nanocomposite films based on liner low density polyethylene (LLDPE), containing of 1 phr silica nanoparticle and 1, 3 and 5 %wt triethoxyvinylsilane as a new coupling were prepared and characterized using FTIR tests, scanning electron microscopy, tensile tests, oxygen and water vapor permeation measurements. Optimization of the technology involved in production of an exfoliated nanocompound is a complex process in which multiple variables and parameters are involved. The results of the study showed that the feed position of the nanoparticle in the double screw extruder is of vital importance in obtaining an exfoliated film. The maximum triethoxyvinylsilane used in the extruder was 3 %wt, for LLDPE/modified silica nanoparticle. There was no exfoliation or intercalation of the silica particle in the absence of triethoxyvinylsilane. The oxygen barrier properties of the LLDPE/modified silica nanoparticle film were significantly better than those of the LDPE/silica nanoparticle film. In addition to barrier properties, the LLDPE/silica/3%TEVS film also had better Young’s modulus and tensile strength than their counterparts without triethoxyvinylsilane. Introduction The unique properties of silanes are used to enhance performance and improve processes in the plastics and rubber industries. Silanes function as coupling and dispersing agents for fillers in rubber and plastics formulations, as polymerization modifiers in the synthesis of polypropylene, and as crosslinking agents for polyethylene homopolymers and copolymers.Vinyl silanes have been used commercially since the 1970s to crosslink polyethylene homopolymer and its copolymers. [1] Vinyltrimethoxysilane and vinyltriethoxysilane are the most common silanes used in the process. In an extruder in the presence of peroxide and heat, the vinyl group will graft to the polyethylene backbone, yielding a silane-modified polyethylene that contains pendant trialkoxysilyl functionality. The grafted polyethylene can then be immediately crosslinked in the presence of a tin catalyst, moisture and heat to create a silane-crosslinked product. The ease of processing and the simple equipment required make this the preferred method of producing crosslinked ethylene polymers and copolymers. The process also allows crosslinking to be delayed until after the grafted product is transformed into its final product configuration. Using the same silanes, it is also possible to copolymerize the vinyl silane with ethylene monomer to make trialkoxysilyl-functionalized polyethylene. This then can be crosslinked in the same manner as the graft version. Silane-crosslinked polyethylene is used for electrical wire and cable insulation and jacketing where ease of processing, increased temperature resistance, abrasion resistance, stress-crack resistance, improved low-temperature properties and retention of electrical properties are needed. Other applications for this technology include: foam for insulation and packaging with greater resiliency and heat resistance and other product and process types, such as film, blow molded articles, All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of TTP, www.ttp.net. (ID: 158.108.64.252-20/03/12,10:22:16)
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sheeting and thermoforming. [1] Industry is developing differentiated films for smaller, easily openable, low-temperature resistant and/or microwaveable packages which increasingly need to support a branding philosophy. New design features like matt film surface help in enhancing the branding. Down gauging flexibility with good overall performance will give additional benefits. Food packaging requires economical, innovative solutions with high package integrity and excellent food quality. [2] Package design is increasingly important in new product promotions. In this paper, we describe the effects of silica nanoparticle and its surface treatment content with triethoxyvinylsilane on the mechanical and barrier properties of LLDPE, which provide important information on the elasticity of the composites over a wide temperature range. The so formed composite films were characterized by FTIR and SEM to identify the dispersion and the morphology of the obtained material, while mechanical and barrier properties were tested with universal testing machine and OTR, WVTR, respectively. Experimental Procedure Raw Materials. Pure LLDPE pallet was L2900F provided by SCG Chemicals. It is non-reinforced, injection moulding, extrusion grade with density of 0.92 g/cc and melt flow of 2.1 g/10 min. Fumed silica nanoparticle was supplied by the Japan, Degussa Company, The hydrophilic nature of nanosilica powders is attributed to the presence of hydroxyl or silanol groups at its surface with primary particle average size of 100 nm. LLDPE/Modified silica nanoparticle film. Silica nanoparticles were dispersed in absolute ethanol under magnetic stirring for 180 minutes. Triethoxyvinylsilane (Sigma-Aldrich) was added (1, 3 and 5 %wt) to the solution and ultrasonically treated for 90 minutes. The modified silica nanoparticles were finally dried at 100°C for 8 hours. The LLDPE/modified silica nanoparticle pellets were prepared by blending LLDPE with silica nanoparticles and other components at 165-185°C using twin-screw extruder. After that the LLDPE/modified silica nanoparticle films were prepared by blown films extruder. The thicknesses of these films were 25 microns. The compositions of the composites films were shown in Table 1. Table 1 Compositions of the LLDPE/modified silica nanoparticle films. A2 A3 A4 A5 Sample Compositions A1 LLDPE (phr) 100 100 100 100 100 Untreated nano-silica (phr) 1 Treated nano-silica (phr) 1 1 1 Triethoxyvinylsilane (%wt) 1 3 5 Characterizations. Surface and bulk characterization of the resultant nanocomposite films were carried out using a Perkin–Elmer RX1 FTIR spectrophotometer model. Surface morphology of LLDPE/modified silica nanoparticle films was examined using a JEOL JSM-651OLV scanning microscope operated at an acceleration voltage of 20 kV and equipped with an energy dispersive system (EDS). Tensile strength, % elongation at break and Young modulus were determined using a LLOYD LRXPlus testing machine with ASTM D882-03. Oxygen transmission rate (OTR) was carried out using MOCON OX-TRAN ®2/21 Oxygen permeability with ASTM D3985-05. Water vapor transmission rate was carried out using 7002 Water vapor permeation analyzer from Illinois instrument with ASTM F1249-06. Results and Discussion FTIR spectroscopy. The use of triethoxyvinylsilane as a coupling agent in silica nanoparticle reinforced LLDPE films is another important microwaveable packaging application. Thus, FTIR spectra of the LLDPE, LLDPE/silica, LLDPE/silica/1%TEVS, LLDPE/silica/3%TEVS and LLDPE/silica/5%TEVS samples as representative examples to identify structures of the compatibilizers are given in Fig. 1 in the wavenumber range of 400–4000 cm-1. For the coupling agent (Fig. 1), shows FTIR spectra of silica nanoparticle at various concentrations of
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triethoxyvinylsilane (1, 3 and 5 %wt). The peaks at 470 and 810 cm-1 are ascribed to the Si-O-Si bending vibration, that at 1100 cm-1 to the Si-O stretching vibration and that at 970 cm-1 to the Si-OH stretching vibration and a strong peaks at about 2960 cm-1 (CH3) and 2860 cm-1 (CH2) can be used to identify the presence of LLDPE phase.
Fig. 1 FTIR spectrum of LLDPE, LLDPE/silica, LLDPE/silica/1%TEVS, LLDPE/silica/3%TEVS and LLDPE/silica/5%TEVS. Scanning electron microscopy. Microstructure of LLDPE/modified silica nanoparticle films was tested with scanning electron microscopy as shown in Fig. 2. SEM images indicate that high degree of dispersion of silica nanoparticle in the LLDPE matrix was obtained at low level of triethoxyvinylsilane content less than 3 wt% and noticeable silica nanoparticle agglomerates were observed with higher level of triethoxyvinylsilane content approximately 5 wt%.
(a) (b) (c) (d) (e) Fig. 2 SEM micrograph of : (a) LLDPE, (b) LLDPE/silica, (c) LLDPE/silica/1%TEVS, (d) LLDPE/silica/3%TEVS and (e) LLDPE/silica/5%TEVS. Adding silica nanoparticles to the base formulation causes some particles to be present on the free surface of the films. As can be seen this roughness is more pronounced in case of pure silica nanoparticle. Comparing the primary particle size and the size of nanoparticles at the surface of the films, it is seen that the nano-silica particles showsome degree of aggregation in all cases. SEM micrographs of the fracture surfaces of the samples containing different silica nanoparticles show a more or less homogeneous dispersion of silica nanoparticles. A very interesting feature of the morphology of the films is the existence of very small cracks in the bulk of the films containing triethoxyvinylsilane (1, 3 and 5 %wt). The extents by which the cracks exist depend on nano-silica surface treatment. Mechanical properties. The mechanical properties of the LLDPE films filled with 1 phr of treated (1, 3 and 5 %wt of triethoxyvinylsilane), untreated silica nanoparticles and neat LLDPE are shown in Fig 3. In the test of % elongation at break, no differences between the LLDPE control and the nanocomposite were observed, demonstrating that the incorporation of nanoparticles did not modify the resistance of the film. In addition, the Young’s modulus and tensile strength of the LLDPE/silica/3%TEVS was higher than for the LLDPE control. With silica nanoparticles, a stiffer material was therefore obtained (higher value in Young’s modulus test), confirming the reinforcing effect of the nanoparticles in the polymeric matrix. Incorporation of the nanoparticles in the polymeric matrix therefore improves the mechanical characteristics of the nanocomposite assayed. Generally, addition of silica nanoparticles treated with triethoxyvinylsilane to ductile polymers increases the yield strength; however, for brittle matrices failure strength is typically decreased. [3]
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(a) (b) (c) Fig. 3 Mechanical properties of LLDPE/modified silica nanoparticle films : (a) tensile strength, (b) % elongation at break and (c) Young’s modulus. Barrier properties. It is generally known that the WVP of polymer/silica nanocomposite films decreases exponentially with increase in coupling agent content or increase in aspect ratio of the silica. The decrease in WVP of polymer/silica composite films is mainly attributed to the tortuous path for water vapor diffusion due to the impermeable silica particles distributed in the polymer matrix with increasing the effective diffusion path length. Oxygen permeability values of the pure LLDPE and the composite films as shown in Fig. 4, the addition of only triethoxyvinylsilane compatibilizer to LDPE increases the permeability slightly. In fact, the addition of triethoxyvinylsilane enhances the polarity of LDPE. This weakens the interaction between polymer and nonpolar oxygen, leading to higher oxygen permeability. Furthermore, the large silane groups on triethoxyvinylsilane increase the space between the polymer chains, leading to more channels for gas transportation. The large side groups of triethoxyvinylsilane affect the structure of LLDPE crystal units, contributing to a lower oxygen barrier with the presence of triethoxyvinylsilane. [1] The decrease in WVP of polymer/silica composite films is mainly attributed to the tortuous path for water vapor diffusion due to the impermeable silica particles distributed in the polymer matrix with increasing the effective diffusion path length. Oxygen permeability values of the pure LLDPE and the composite films as shown in Fig. 4, the addition of only triethoxyvinylsilane compatibilizer to LDPE increases the permeability slightly. In fact, the addition of triethoxyvinylsilane enhances the polarity of LDPE. This weakens the interaction between polymer and nonpolar oxygen, leading to higher oxygen permeability. Furthermore, the large silane groups on triethoxyvinylsilane increase the space between the polymer chains, leading to more channels for gas transportation. The large side groups of triethoxyvinylsilane affect the structure of LLDPE crystal units, contributing to a lower oxygen barrier with the presence of triethoxyvinylsilane. [4]
(a) (b) Fig. 4 Barrier properties of LLDPE/modified silica nanoparticles : (a) OP and (b) WVP.
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Conclusions The FTIR spectrum of nanocompounds of LLDPE demonstrate additivation of the silica nanoprticles in the polymeric matrix. SEM is useful techniques for determining whether nanocompounds are intercalated or exfoliated. The technique used in producing the film, the screw used, the kind of polymeric matrix and the mixing time are all of great importance in determining whether the final product is intercalated or exfoliated. The optimal mixing time differs for each nanosilica and polymeric matrix, and must therefore be determined in each case. Nanoparticles of silica treated with triethoxyvinylsilane have the capacity to optimize barrier properties, thereby improving the quality of packaged foods. Study of nanocompounds and their effects on packaging, and the foods packaged within the films, are of great importance for increasing the shelf life of foods. However, it is also necessary to study safety aspects associated with the use these nanocompounds in packaged foods, in terms of health and environment, and the effect of the migration of the constituents of the polymers and their possible migration into foodstuffs. Optimization of the technique of producing a nanocompound is an arduous and complex process in which multiple variables and parameters are involved, all of which must be studied to obtain the best film for the purposes intended. Acknowledgements The authors wish to acknowledge the financial support from the Graduate School Kasetsart University and Young Scientist and Technologist Programme (YSTP). In addition, the authors would like to thank Science & Innovation center, PTT Chemical Public Company Limited for providing LLDPE resin and instrument. References [1] S. Hyun Shin, H. Hyung Kim: J. Ind. Eng. Chem Vol. 7 (2001), p.147-152 [2] L.G. Robertson, 2006. Food Packaging: Principle and Practice. 2nd. Tayloy&Francis group, Florida [3] H. Azizi, J. Morshedian, M. Barikani, M. H. Wagner: eXPRESS Polymer Letters Vol. 4 (2010), p.252–262 [4] W. Brostow: CHEMISTRY & CHEMICAL TECHNOLOGY Vol. 2 (2008), p.27-32
Key Engineering Materials II 10.4028/www.scientific.net/AMR.488-489
Preparation of LLDPE/Modified Silica Nanoparticle with Triethoxyvinylsilane Film for Microwaveable Packaging 10.4028/www.scientific.net/AMR.488-489.1525
