알킬나노셀룰로즈의 제조 및 분산성 향상 연구

Abstract

본 연구에서는 Microcrystalline cellulose (MCC)를 나노화하여 나노셀룰로즈 (NC)를 제조하고, 제조된 NC와 Bromoalkane (bromooctane, bromododecane)을 SN2 반응에 의해 반응시켜 셀룰로즈의 하이드록실 그룹을 알킬 그룹으로 치환하였다. 이를 옥틸 셀룰로즈 (Octyl cellulose, OC)와 도데실 셀룰로즈 (Dodecyl cellulose, DC)라 명명하였다. 제조된 OC와 DC를 보강재로 Polylatide (PLA)와 혼입하여 복합재료 필름을 제조하였다. Polylactide (PLA)는 바이오메스로부터 유래한 친환경 고분자 소재로써, 기존 석유화학 기반 고분자를 대체할 소재로 각광을 받고 있지만 상업화된 석유화학 기반 고분자에 비해 상대적으로 낮은 기계적 강도를 갖고, 열에 의한 변형에 취약하다는 단점이 있다. 셀룰로즈는 자연계에서 추출되는 가장 흔한 유기화합물 중 하나로 강한 기계적 물성으로 인해 생분해성 보강재로 각광받고 있다. 나노 크기의 셀룰로즈의 경우, 매우 강한 기계적 물성을 보이며, 열팽창계수가 낮아 PLA의 단점을 개선하여 친환경 고성능 복합재료 제조에 적합한 소재이다. 하지만 셀룰로즈는 단량체 당 3개의 하이드록실 그룹을 갖기 때문에, 분자 내 또는 분자 간 수소결합이 매우 강하여 고분자 복합재료 제조 시 응집이 잘 일어나 분산이 어렵다. 이를 개선하기 위하여 소수성이 큰 알킬 그룹을 셀룰로즈의 하이드록실 그룹에 치환하는 연구를 진행하였다. 본 연구에서는 FT-IR과 13C-NMR 분석을 이용해 셀룰로즈의 알킬레이션이 성공적으로 이루어짐을 확인하였다. 접촉각 측정으로 알킬 그룹에 의한 소수성 부여가 확인되었으며, 표면 에너지 계산으로 극성이 낮은 환경에서 셀룰로즈의 분산성이 향상될 수 있다는 결과를 보였다. 열안정성, 결정 구조 등이 조사되었다. 또한, PLA복합필름의 기계적, 열적 물성이 향상되었으며, PLA 필름과 상대 투과도를 비교하여 투명하면서 기계적 강도가 향상된 PLA 필름이 제조됨을 확인할 수 있었다. |The substitution of the hydrophobic long alkyl chain for the hydroxyl group in cellulose was successfully performed to improve the dispersion in non-polar environment. Furthermore, PLA/alkyl cellulose composite films with improved properties were successfully prepared. Nanocellulose tends to be aggregated due to the hydrogen bonding between three of the hydroxyl groups in each repeating unit, resulting in poor dispersion in the non-polar polymer matrix. In this research, to improve the dispersion of cellulose particles in the polymer matrix, a long hydrophobic alkyl chain was substituted for hydrogen in the hydroxyl group of cellulose via a bimolecular nucleophilic substitution (SN2) reaction with alkyl bromide. The octyl (-C8H17) and dodecyl (-C12H25) groups were applied to this reaction, which is faster and simpler compared to other substitution reactions. The chemical structure of octyl and dodecyl cellulose was identified by the Fourier transform infrared (FT-IR) and nuclear magnetic resonance (NMR) analysis. The contact angle with water and methylene iodide was measured to calculate the surface energy of alkyl nanocellulose. The surface energy was decreased by the substituted alkyl chain. The thermal properties, morphology and crystal structure of octyl and dodecyl cellulose were also investigated to qualify the probability as a reinforcement. Furthermore, polylactide/alkyl cellulose composites were prepared to make certain of sufficient dispersion of alkyl cellulose on the polylactide matrix. The thermal properties and mechanical properties of polylactide composite films were investigated. The optical transmittance of the polylactide composites was measured to confirm the relative dispersity.; The substitution of the hydrophobic long alkyl chain for the hydroxyl group in cellulose was successfully performed to improve the dispersion in non-polar environment. Furthermore, PLA/alkyl cellulose composite films with improved properties were successfully prepared. Nanocellulose tends to be aggregated due to the hydrogen bonding between three of the hydroxyl groups in each repeating unit, resulting in poor dispersion in the non-polar polymer matrix. In this research, to improve the dispersion of cellulose particles in the polymer matrix, a long hydrophobic alkyl chain was substituted for hydrogen in the hydroxyl group of cellulose via a bimolecular nucleophilic substitution (SN2) reaction with alkyl bromide. The octyl (-C8H17) and dodecyl (-C12H25) groups were applied to this reaction, which is faster and simpler compared to other substitution reactions. The chemical structure of octyl and dodecyl cellulose was identified by the Fourier transform infrared (FT-IR) and nuclear magnetic resonance (NMR) analysis. The contact angle with water and methylene iodide was measured to calculate the surface energy of alkyl nanocellulose. The surface energy was decreased by the substituted alkyl chain. The thermal properties, morphology and crystal structure of octyl and dodecyl cellulose were also investigated to qualify the probability as a reinforcement. Furthermore, polylactide/alkyl cellulose composites were prepared to make certain of sufficient dispersion of alkyl cellulose on the polylactide matrix. The thermal properties and mechanical properties of polylactide composite films were investigated. The optical transmittance of the polylactide composites was measured to confirm the relative dispersity.