에폭시와 제올라이트 계면의 형상

이재영, 최형기*, 김상욱

서울시립대학교 화학공학과, *산업자원부 기술표준원 화학부

Morphology of the Interface between Epoxy and Zeolite

J. Y. Lee, H. K. Choi* and S. W. Kim

Dept. of Chem., The Univ. of Seoul, *Agency for Technology & Standards, MOCIE

Introduction

With the increasing demands for new polymer composites in many applications, researchers have investigated the characteristics between polymer matrix and inorganic filler. Many species of inorganic fillers, such as silica, calcium carbonate, mica, talc, carbon black, kaolin and metal powder have been used to improve the mechanical, thermal, electrical, rheological and optical properties[1∼8]. The properties of the polymer composites are affected not only by the characteristics of the matrix and filler but also by the characteristics of the interface[1∼3]. In general, two dissimilar components of the composites have little affinity, for the surface of the inorganic filler is hydrophilic and that of the matrix is hydrophobic. So, the micro crack and craze are initiated from the interface and the mechanical fracture take place, finally. It is the reason why the characteristics of the interface is the most important factor to determine the properties of the polymer composites. Many techniques are studied and developed to improve the affinity between matrix and inorganic filler at the interface and one of the most well-known methods is to connect the dissimilar components by coupling agent[4∼6].

Experiment

Epoxy resin was diglycidyl ether of bisphenol A(DGEBA)/4,4'-methylene dianiline (MDA)/malononitrile(MN) system and inorganic filler was clinoptilolite type natural zeolite(under 325 mesh) which was plentifully produced in Korea. The silane coupling agent was □-glycidoxypropyl trimethoxy silane(A-187, Union Carbide Co.).

O

□   □

CH2CHCH2O(CH2)3Si(OCH3)3

The surface of the natural zeolite was treated with coupling agent by the following procedure. Methanol : water = 9 : 1 at weight ratio was mixed with 1.0 and 2.0 wt% of A-187 and the pH of the mixtures was adjusted to 3.5 by the addition of acetic acid. Natural zeolite was added to the mixtures of pH=3.5 and treated for 12 hrs at 25□. The silane treated natural zeolite was dried for 12 hrs at 110□ and ground into the powder under 325 mesh. They were stored at desiccator to prevent the adsorbing water molecules in the air.

To observe the interface morphology, zeolite-dispersed epoxy composite was cured and tensile test was carried out by universal testing machine at the cross-head speed of 5 mm/min. The morphology of the interface and fractured surface was observed by SEM.

(A)                                      (B)

Fig.1 The morphology of the fracture       surface in DGEBA/MDA/MN        system without natural zeolite.       (A) a crack initiation region

(B) a slow crack-growth region

(C) a fast crack-growth region

(C)

Results and Discussion

Fig.1 shows the morphology of the fracture surface in epoxy system without natural zeolite that failed in tension and it can be divided into three characteristics regions. The crack is initiated from the center of the mirror-like circular periphery of Fig.1(A) which is surrounded by smooth river markings. The smooth river markings in Fig.1(B) are located between the mirror-like region and the rough parabolas in Fig.1(C). The mirror-like and smooth river marking region are associated with the slow velocity of crack growth and the rough parabola region is the result of complex, unstable and brittle failure. The surface roughness is primarily caused by the generation of secondary crack fronts ahead of the primary crack front and the interconnection of these crack fronts from different planes. The fracture energy involved in the slow crack growth is far higher than that of the fast[14].

However, when natural zeolite was added, the morphology of the surface was more complex and there was no characteristics regions regardless of the silane treatment(Fig.2). The interface between zeolite and matrix is a new crack initiation region because of the difference of linear expansion coefficient between epoxy matrix and zeolite filler and the morphology become more complex. So, tensile strength decreased with the increment of zeolite content.

Fig.3 shows the morphology of the interface and the surface zeolite particle

Fig.2 The morphology of the fracture       surface in DGEBA/MDA/MN         system with the 20 phr of the        1.0 wt% silane-treated natural         zeolite.

treated with different concentration of silane coupling agent. There is no polymer traces on the surface of the untreated zeolite and there is no adhesion at the interface. However, the surface of the zeolite is coated with the polymer and the interface adhesion is modified, when the natural zeolite treated with 1.0 wt% concentration is used. The morphology of the interface treated with 2.0 wt% is well adhered, so there is no boundary at the interface and it made the stress disperse to the matrix around the zeolite. So, the tensile strength increased with the increasing concentration of silane coupling agent.

(A)                                      (B)

Fig.3 The interface morphology between       natural zeolite and natural zeolite.

Silane-treated concentration:

(A) untreated, (B) 1.0 wt% and         (C) 2.0 wt%

Conclusion

The surface morphology of the epoxy system without natural zeolite was divided into three characteristics regions : one was initiation region, another was smooth region of slow crack-growth, and the other was rough region of fast crack-growth. However, when natural zeolite was added, the morphology of the surface was more complex and there was no characteristics regions regardless of the silane treatment.

The adhesion of the interface between epoxy resion and zeolite particle was more improved by the increasing concentration of silane coupling agent. So, the tensile strength increased with the increasing concentration of silane coupling agent.

References

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