噴墨列印所需之纖維素奈米微晶的膠體性質與尺寸特性探討

Abstract

纖維素為地表蘊藏量最為豐富的可再生、生物可降解資源。而將纖維素微纖維中的結晶區萃取而出，則可以得纖維素奈米微晶。本研究關注以噴墨列印法將纖維素奈米微晶應用於可設計規則性排列之商品，所需探討的纖維素奈米微晶水溶液的相關性質。本研究以纖維素奈米微晶之製程著手：試驗不同的製備條件、尋找最適者。成功於特定條件下製備尺寸落在奈米維度，近似於商用纖維素奈米微晶的產品。亦發現產品顏色會隨處理溫度與處理時間的拉長而轉深，並於熱分析中得到較多殘餘，應是較強的水解條件會帶給纖維素奈米微晶更多硫酸基所造成。其次為纖維素奈米微晶溶液之膠體性質探討，並與理論模型比對。模型比對可以證實商用的及自製纖維素奈米微晶的表面有酸水解造成之強負電荷，並其棒狀型態與硫酸基造成之表面化學特性亦須納入考量。此外，也探討其黏度性質。除剪切稀釋特性需考慮外，以黏度結果與噴墨印表機之墨水要求進行比對與篩選，進行噴墨列印測試。結果顯示纖維素奈米微晶墨水於紙材上乾燥時，會形成內縮力，進而導致紙材表面塗層的破壞與紙張彎曲。因此，若不希望產品具有設計之外的彎曲，有好塗層的紙材較適合做為纖維素奈米微晶墨水之噴墨基材。

Cellulose is the most abundant of renewable and biodegradable polymer on Earth. Cellulose nanocrystals, in short, CNCs, are the crystalline region of cellulosic chains on nanoscale. As to a new application of CNCs to inkjet printing for patterning type products, exploring properties of CNC suspensions would be necessary. Thus, a CNC preparation test was conducted and provided an optimal acid hydrolysis condition. The resulting CNCs exhibited nanoscale dimensions, and a crystallinity index similar to the commercial one. A gradient of color changes of CNCs was found with an increasing hydrolysis duration and hydrolysis temperature. Introduction of sulfate groups was assumed by sulfuric acid hydrolysis. Strong conditions are supposed to introduce more sulfate groups on CNCs, which may act as flame retardants and thus increase the amount of char residue. Colloidal properties of CNCs obtained via sulfuric acid hydrolysis were investigated. A strong negative surface charge caused by sulfuric acid hydrolysis was confirmed by fitting the data spots to theoretical equations; in addition, a cylindrical shape and a high-charged surface morphology caused by sulfate groups of CNCs were suggested. Results from viscosity measurements showed obvious shear thinning phenomena of CNC suspensions at high concentrations. A specific concentration of CNC which were suitable for inkjet use in terms of the viscosity requirements of inkjet printers was applied in printing tests. Finally, a paper substrate with a mechanically strong surface coating is suggested to be applied for prevention from destruction due to shrinkage force.