Synthesis of tung oil-based thermoset resin and its thermal·mechanical properties

Tung oil을 이용한 바이오 기반 열경화성 수지 합성 및 이의 열적·물리적 특성 연구

Abstract

Various investigations of vegetable oil extracted from natural resources are underway because of their low cost and environmental value. On the other hand, the double bonds in vegetable oil should be substituted to other high reactive functional groups due to their low reactivity for synthesizing bio-polymeric materials. ${\alpha}$-eleostearic acid, which consists of a conjugated triene, is the main component of tung oil, and the conjugated triene allows tung oil to have higher reactivity than other vegetable oils. In this study, tung oil was copolymerized with styrene and divinylbenzene to make a thermoset resin without any substitution of functional groups. The thermal and mechanical properties were measured to examine the effects of the composition of each monomer on the synthesized thermoset resin. The results showed that the products have only one Tg, which means the synthesized thermoset resins are homogeneous at the molecular level. The mechanical properties show that tung oil acts as a soft segment in the copolymer and makes a more elastic product. On the other hand, divinylbenzene acts as a hard segment and makes a more brittle product.

식물유는 자연 유래 물질로 낮은 가격 및 친환경적이라는 장점으로 최근 다양한 연구가 진행되고 있다. 하지만 식물유 내의 이중결합의 낮은 반응성으로 인해 고분자 합성의 기반 물질로 사용하기 위해서는 반응성이 높은 관능기로 치환하여 사용하는 경우가 많다. Tung oil은 ${\alpha}$-eleostearic acid를 주성분으로 하는데, 이 구조는 3개의 이중결합이 공명구조로 되어있기 때문에 다른 식물유와는 달리 높은 반응성을 보인다. 본 연구에서는 이러한 tung oil을 styrene 및 divinylbenzene 등의 단량체와 양이온 중합을 통해 tung oil의 관능기 치환 과정이 없는 열경화성 수지를 합성하였으며, 각 단량체의 조성이 합성된 열경화성 수지에 미치는 영향을 확인하기 위해 열적 기계적 물성을 측정하였다. 그 결과, tung oil-styrene-divinylbenzene 공중합체는 단일 Tg를 갖는 균일(homogeneous)한 열경화성 고분자를 형성하는 것을 확인하였으며, 기계적 물성의 변화를 통해 tung oil 및 styrene은 soft segment로써 합성된 공중합체에 탄성(elasticity)을 부여하고, divinylbenzene은 hard segment로 작용하여 합성된 공중합체에 취성(brittleness)을 부여하는 것을 확인하였다.

Fig. 1. Structure of α-eleostearic acid

Fig. 2. Alkyl esterification of triglyceride

Fig. 3. DMA results of TO-Styrene-DVB copolymers (a) Storage modulus of copolymers depending on TO composition (b) Tan δ of copolymers depending on TO composition (c) Storage modulus of copolymers depending on Styrene/DVB composition (d) Tan δ of copolymers depending on Styrene/DVB composition

Fig. 4. Cross-linking density of TO-styrene-DVB copolymers : (a)Cross-linking density of copolymers depending on TO composition (b)Cross-linking density of copolymers depending on Styrene/DVB composition

Fig. 5. Tensile properties and impact strength of TO-styrene-DVB copolymers (a) Tensile properties of copolymers depending on TO composition, (b) Impact strength of copolymers depending on TO composition, (c) Tensile properties of copolymers depending on Styrene/DVB composition, (d) Impact strength of copolymers depending on Styrene/DVB composition

Table 1. Compositions and symbols of TO-Styrene-DVB copolymers

Table 2. DMA results of TO-Styrene-DVB copolymers

Table 3. Mechanical properties of TO-Stytene-DVB copolymers