Nylon/EVOH 블렌드의 물성에 관한 연구

김종민, 여상길, 박찬석, 이종훈, 이기준, 김성우*

서울대학교 화학공학과

경기대학교 화학공학과*

A Study on the Properties of Nylon/EVOH Blends

Jong Min  Kim, Sang Gil Yeo, Chan-Seok Park, Chong Hoon Lee, , Ki-Jun Lee, Seong Woo Kim*

Department of Chemical Engineering, Seoul National University

Department of Chemical Engineering, Kyonggi University*

Introduction

Plastic materials with good oxygen and solvent barrier properties have many advantages including light weight, flexibility, strength, transparency, and ease of processing in comparison to metal and glass for use in packaging and solvent containers.1-2

Ethylene-vinyl alcohol copolymer (EVOH) has been widely used as food packaging materials because of its superior gas barrier property, excellent transparency, and high oil resistance.3-5 However, EVOH has a few shortcomings such as relative high brittleness, high cost, and difficulty of processing. On the other hand, nylon that is more advantageous in cost relative to EVOH exhibits high resistance to the permeation of organic solvents, and also has good impact strength.

In this work, thus, blending EVOH with nylon was attempted to improve barrier property of both oxygen and organic solvents, and to enhance mechanical properties as well as to secure the price competition. The effects of composition in nylon/EVOH blend system on the rheological, morphological, thermal, mechanical, and barrier property were investigated. The compatibility of this blend system was also evaluated by performing FTi.r. and morphological analysis.

Experimental

Nylon(2835TF) supplied by Hyosung Co. was selected. It is a copolymer of nylon 6 and nylon 66 with mole ratio of 17 : 83, and melting temperature of 191.5℃. Melting temperature of the resin was much lower than pure nylon 6 and nylon 66 resulting in easier extrusion processing. An ethylene vinyl alcohol copolymer(EVOH, EP-E105B) obtained from Kuraray Co. was used. This EVOH is a high barrier resin containing 44% moles of ethylene with good optical clarity. It is a blow molding grade having density of 1.14 g/cc, melting temperature of 166.2℃, and melt flow index of 5.5 g/10min. Compatibilizer as a interfacial agent was not used because EVOH and nylon are virtually compatible due to hydrogen bonding interactions.

Nylon/EVOH blends were prepared with Haake Rheomix 600 mixer. They were melt mixed for 7 minutes at 220℃ and 50rpm. Thermal property measurements were carried out under nitrogen atmosphere by a Dupont thermal analyzer 2010 model differential calorimeter to evaluate the effect of the component ratio of blends on the melting and crystallization behavior of the blends. Rheological properties of two virgin polymers and blends were measured by Rheometrics Mechanical Spectrometer (RMS 800) with rotational parallel plate fixtures. The morphology of the blends was observed using a scanning electron microscope(JSM-T200). The blend samples were prepared by freeze-fracture in liquid nitrogen, and the fracture surfaces were coated with a thin layer of gold. The oxygen permeability of blend films was measured by the apparatus consisting of permeation cell, pressure transducer, upstream/downstream gas reservoir, and A/D converter, which was designed according to ASTM D3985 method.

Result and Discussion

Thermal property

Figure 1 shows the effect of the component ratio of blends on the melting temperature peaks. The melting thermograms were obtained at the heating rate of 10℃/min. The melting temperatures for nylon and EVOH appear separately, and the melting temperature of each resin decreased as the contents of the other resin increased. In the case of nylon, two melting peaks corresponding to the nylon 6 and nylon 66 could be observed at more than 50 wt% of nylon. But at lower content of nylon below 50 wt%, only melting temperature peak corresponding to nylon 66 occupying larger amount in copolymer was detected beacuse the peak corresponding to nylon 6 was shifted to the peak of EVOH.

Figure 2 shows the effect of the component ratio of blends on the crystallization temperature peaks. It should be noted that only peak of major component was observed and the crystallization temperature of one component decreased as the content of the other component increased in a similar pattern to the melting behavior. This may be attributed to the miscibility between nylon and EVOH.

Rheological property

The variation of complex viscosity of nylon/EVOH blends having various compositions is shown in Figure 3. The complex viscosities of blends were measured at 220℃. It can be seen that EVOH has lower viscosity and exhibits more shear sensitivity than nylon. The viscosities of the blends increased with increasing the content of nylon up to 50wt%, and then decreased above that level of content. In particular, all blends have a higher viscosity than both pure nylon and EVOH resin, since deformation resistance to shearing action is increased due to miscibility in nylon/EVOH blends. The positive deviation in viscosity generally occurs when there are strong interactions among droplets at low rate of shear, or when the blend has an interlocked morphology.

Oxygen permeability

The measured oxygen permeability as a function of nylon content is depicted in Figure 4.  shows the effect of the component ratio of blends on blend films. As can be seen, the oxygen permeability of nylon/EVOH system increases as EVOH weight fraction is increased. The logarithm of permeability of this nylon/EVOH blend was correlated linearly with the weight fraction of either of components of the blend, exhibiting slight deviations of experimental results from additive rule. This result can be frequently observed for a miscible blend system.

Reference

1. Elemans, P. H. M.; van Gisbergen, J. G. M.; Meijer, H. E. M. In Integration

of Fundamental Polymer Science and Technology,  P. J. Lemstra, L. A.

Kleintjens, Eds.; Elsvier Appl. Sci.: London 1988; Volume 2.

2. Meijer, H. E. M.; Lemstra, P. J.; Elemans., P. H. M. Makromol Chem,

Macromol Symp 1988, 16, 113.

3. C. A. Finch, Polyvinyl Alcohol, John Wiley and Sons, New York, 1992.

4. W. J. Karos, Barrier Polymers and Structures, ACS Symposium Series 423,

American Chemical Society, Washington, DC, 1989.

5. K. M. Finlayson, Plastic Film Technology: High Barrier Plastic Film for

Packaging, Technomic Publishing Co., Lancaster, Pa. (1989)

Fig.1. Melting temperatures of nylon/EVOH blends.

Fig.3. Complex viscosity vs. frequency for nylon/EVOH blends at 220℃

Fig.2. Crystallization temperatures of nylon/EVOH blends.

Fig.4. Oxygen permeability vs. nylon content for nylon/EVOH blends.