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이재효,손승모,유중재,김상우,Yi Jin Woo,성동기 한국유변학회 2023 Korea-Australia rheology journal Vol.35 No.1
Thermoplastic resin transfer molding (T-RTM) of polyamide 6-based composite is one of the promising process to massproduce an environmentally friendly textile composite with recyclable thermoplastic resin, in which ε-caprolactam monomer with low viscosity is injected and in situ polymerized into the fabric. The side reactions caused by water in the anionic polymerization process of the monomer is a crucial problem for fabricating the composite with a high quality. In this study, we introduced zeolite, a porous ceramic water-absorbing particle, into the ε-caprolactam to improve the moisture sensitivity during the anionic polymerization. The selective water-absorbing eff ect of zeolite particle was verifi ed by measuring the monomer conversion, viscosity-average molecular weight, and viscosity change during polymerization, and mechanical properties of the resultant carbon fi ber reinforced polyamide composite were investigated. It is expected that processability of the T-RTM is remarkably improved by reducing both the drying time during process and quality deviation of the composite by variation of humidity, which can make T-RTM process a viable technology for mass-production of thermoplastic composites.
반응액상성형에서 ε-카프로락탐의 음이온 중합에 따른 점도 거동 평가
이재효,강승인,김상우,이진우,성동기 한국복합재료학회 2020 Composites research Vol.33 No.2
최근 내화학성, 내마모성 및 내충격성이 뛰어나면서 재활용이 가능한 열가소성 폴리아미드 기반 복합재료를 제조하는 기술을 개발하기 위한 연구가 활발하다. 특히, 열가소성 고분자는 높은 점도로 용융 상태에서의 가공이 힘들기 때문에 저점도 단량체 상태로 금형 내부로 주입하면서 동시에 중합을 시키는 반응액상성형 공정이큰 주목을 받고 있다. 그러나 단량체인 ε-카프로락탐은 중합속도가 매우 빠르고 외부 환경에 매우 민감하기 때문에 수지 함침과 중합 반응을 동시에 제어하면서 최적 공정조건을 확보하는 데 많은 어려움을 겪고 있는 실정이다. 따라서 본 연구에서는 ε-카프로락탐의 음이온 중합과정에서 주요한 공정 변수인 점도 변화 거동을 관찰하였고 ε- 카프로락탐의 빠른 중합, 낮은 점도, 수분 민감성에 따른 측정상의 문제 원인을 분석하여 개선책을 제시하였다. 개선된 점도 측정 방법에 대한 재현성과 신뢰성은 여러 상대습도에 대한 점도 측정 그리고 외부 환경(수분, 산소)과차단된 상황에서의 중합과 개선된 점도 측정 결과와의 비교를 바탕으로 검증하였으며, 이는 복합재료 반응액상성형 공정의 제어 인자로 활용함으로써 공정 최적화에 도움이 될 것으로 기대된다. Recently, fabrication process of thermoplastic polyamide-based composites with recyclability as well as impact, chemical, and abrasion resistance have been widely studied. In particular, thermoplastic reactive resin transfer molding (TRTM) in which monomer with low viscosity is injected and in-situ polymerized inside mold has received a great attention, because thermoplastic melts are hard to impregnate fiber preform due to their very high viscosity. However, it is difficult to optimize the processing conditions because of high reactivity and sensitivity to external environments of the used monomer, ε-caprolactam. In this study, viscosity as an important process parameter in TRTM was measured during in-situ anionic polymerization of ε-caprolactam and the solutions for problems caused by high polymerization rate and sensitivity to moisture and oxygen were suggested. Reliability of the improved measurement technique was verified by comparing the viscosity behavior at various environmental conditions including humidity and atmosphere, and it is expected to be helpful for optimization of TRTM process.
후지체공 흰쥐에서 가자미근과 내측비복근의 기계적 특성 및 MHC 단백질의 변화
이재효,이문영,이성호 圓光大學校 醫科學硏究所 2002 圓光醫科學 Vol.17 No.1
The present study was designed to evaluate the changes of mechanical properties of contraction and myosin heavy chain (MHC) protein in the soleus and medial gastrocnemius muscles following hindlimb suspension in rats. After 14 days of hindlimb suspension, contraction time, half relaxation time, maximum twitch tension, maximum tetanic tension and fatigue index were measured in the soleus and medial gastrocnemius muscles, also MHC was measured in those muscles by means of immunohistochemical study. Body weight and muscle weight were decreased significantly in hindlimb suspended rats. In hindlimb suspended rats, mechanical properties including contraction time, half relaxation time, maximum twitch tension and maximum tetanic tension were decreased significantly and muscle fatigue was increased, which was more prominent in the soleus muscle than the gastrocnemius muscle. MHC type Ⅰ was decreased significantly and MHC type Ⅱx which was not observed in control was increased in the soleus muscle following hindlimb suspension, which represented that the slow muscle fibers converted to the fast muscles fibers. In the medial gastrocnemius muscle following hindlimb suspension, MHC type Ⅰ and type Ⅱx were decreased significantly and MHC type Ⅱb was increased significantly. These results suggest that MHC of the slow muscle fibers converted to MHC of the fast muscle fibers during hindlimb suspension, which was corresponded to changes of mechanical properties of contraction.