상용화제가 PP/PA 블렌드의 물성에 미치는 영향

이종환, 김종민, 이기준, 남재도*, 김성우**

서울대학교 응용화학부, 성균관대학교 고분자공학과*, 경기대학교 화학공학과**

Influence of compatibilizer on the Properties

of Polypropylene/Polyamide Blends

Jong Hwan Lee, Jong Min Kim, Ki-Jun Lee, Jae-Do Nam*, and Seong Woo Kim**

Department of Chemical Engineering, Seoul National University

Department of Polymer Science and Engineering, Sung Kyun Kwan University*

Department of Chemical Engineering, Kyonggi University**

Introduction

Mixing two or more polymers together to produce blend is a well- established strategy for achieving a specified physical property, without the need to synthesize specialized polymer system. In recent years, food packag- ing films with high barrier properties have been produced by blending polyolefin and impermeable polymers.(1-3)

Polypropylene(PP) is a polymer with good mechanical and barrier proper- ties to H2O, but it has poor barrier property to O2 and CO2. On the other hand, Polyamide(PA) has high barrier properties to gases, such as O2 and CO2, and high resistance to hydrocarbons.(4) However, blending of two polymers usually leads to immiscibility, and the desired properties are not achieved without a third component, i.e., a compatibilizer which is able to increase the interfacial adhesion between major and minor phase. Besides that, compatibilizer induces changes in other properties and morphology. These effects were attributed to the reaction, during melt mixing, through the homopolymers and the functional groups present in the third component.(5)

The ultimate behavior of the polymer blend, to a large extent, depends on the morphology of the blend, such as the size and the shape of the dispersed phase, and on the nature of the interface between the two phases.(6-7)

In this study, the effects of compatibilizer on the morphological, rheological, thermal, and mechanical properties of PP/PA blends were investigated.

Experimental

For the continuous phase(matrix phase), a film grade PP(HF21AGT, M.I.= 2.0g/10min, Tm=160.9℃, Tc=116.3℃)was chosen which had been manufactured by Samsung General Chemicals. For the dispersed phase as a barrier material, PA(2835TF, a copolymer of Nylon 6 and Nylon 66, Tm=191.5℃, Tc=143.9℃) was obtained from Hyosung Co. The compatibilizer used in this study was polypropylene grafted with 0.3 wt% maleic anhydride(PP-g-MAH, PO1015;  Tm=143.9℃, Tc=102.3℃) obtained from Exxon Co.

Compatibilized PP/PA blends were prepared using a Haake Rheomix 600 mixer. The blends were melt mixed for 7 minutes in a mixer at 230℃ and 50rpm. Rheological properties of both virgin polymers and blends were measured both by a Rheometrics Mechanical Spectrometer(RMS 800) fitted with a rotational parallel plate fixtures and by a capillary viscometer(Rosand RH720) with a capillary die (L/D=16). 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.

Thermal property measurments were carried out under nitrogen atmosphere by a Dupont thermal analyzer 2010 model differential calorimeter in other to evaluate the effect of the compatibilizer added to the blends on the melting and crystallization behavior of the PP/PA blends. Tensile strength and Elongation at break were measured by an Instron testing machine(Model : IX series 6.05) with a cross head speed of 50mm/min. Five samples were tested in each case, and the standard deviation was less than 10%.

Result and Discussion

Rheological property

In the binary blend system, the viscosity of each resin and the viscosity ratio of the dispersed phase to the continuous phase(□=□d/□m) are important factors in controlling the blend morphology. It was exhibited that because of shear sensitivity of viscosity of PP, the viscosity ratio increases gradually with increase of shear rate, falling into the range between 0.4 and 2.0 in the practical shear rate from 101 to 103 sec-1. The compatibility of immiscible PP/PA blends was investigated from the variation of rheological property by adding the compatibilizer. The effect of the content of PP-g-MAH on the complex viscosity of the PP /PA(80/20) blends was shown in Figure 1. The viscosity increased with the addition of compatibilizer until 4phr, and then decreased gradually. In case the content was less then 4phr, compatibilizer improves the interfacial adhesion due to the reaction between PP-g-MAH and PA during melt mixing. However, the addition of compatibilizer above that level exhibits no more contribution in increasing the interfacial adhesion, and decreases the viscosity of the blends due to lower viscosity of PP-g-MAH relative to other virgin polymers.

Morphology

Incompatible blends are characterized by sharp interface and irregular domain size. In this study, the compatibilizer(PP-g-MAH) was used to enhance the interfacial adhesion between continuous and dispersed phase and to obtain stable morphology in immiscible binary blends of PP and PA. The uncompatibilized blend shows large and coarse domains, and the sizes of domains are very diverse. By addition of the compatibilizer to the PP/PA(80/20) blends, the dimension of the PA domains decreased with increasing the amount of PP-g-MAH, and the interface became indistinct. These results also demonstrated the addition of PP-g-MAH enhanced the interfacial adhesion between the two phases.

Thermal property

Figure 2 shows the cooling thermograms obtained at a cooling rate of 10℃/min of the PP/PA(80/20) blends which were compatibilized with various amount of PP-g-MAH. The exothermic peak temperature of PP does not change significantly with the addition of PP-g-MAH and stays at an almost constant temperature of about 116-119℃. In case of PA, the addition of PP-g-MAH up to 0.5phr does not cause meaningful changes. However, with further addition of PP-g-MAH, the exothermic peak temperature does not exist any more. But the melting peak temperatures of PP and PA are not varied with the addition of PP-g-MAH.

Mechanical property

Tracing the variation of tensile property has been a method of evaluating qualitatively the compatibility by adding compatibilizer. The effect of compatibilizer on the tensile properties of the PP/PA(80/20) blends is shown in Figure 3 and 4. The elongation and tensile strength are much improved in comparison with the uncompatibilized blend. The inferior mechanical properties of the uncompatibilized blend can be explained by the presence of large and coarse domains and poor adhesion between the two phases. By adding a compatibilizer, the sizes of dispersion phases became small and uniform, and stronger interfacial adhesion was acquired. In particular, the tensile strenght at break of the blends was initially increased with increasing of compatibilizer content up to 2 phr, and then decreased. This optimum compatibilizer content for tensile strength was believed to be a result of competition between the improved interfacial adhesion and the compatibilizer's own inferior strength relative to the virgin resin.

References

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2. G. W. Lohfink and M. R. Kamal, Polymer Engineering and Science, 33, 21,       1404 (1993)

3. S. A. Jabarin and W. J. Kollen, Polymer Engineering and Science, 28, 1156       (1987)

4. R. M. Holsti-Miettinen, K. P. Perttila, J. V. Seppala, and M. T. Heino,         Journal of Applied Polymer Science, 58, 1551 (1995)

5. M. Xanthos and S. S. Dagli, Polymer Engineering and Science, 31, 13, 929       (1991)

6. P. M. Subramanian, Polymer Engineering and Science, 25, 8, 483 (1985)

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Fig.1. Complex viscosity of PP/PA     Fig.2. DSC cooling thermograms of

blends versus frequency at            PP/PA blends with various

230℃.                                amount of PP-g-MAH.

Fig.3. Elongation at break of PP/PA    Fig.4. Tensile strength at break of

blend films as a function of            PP/PA blend films as a

the amount of compatibilizer.           function of the amount of

compatibilizer.