Phase Structure and Mechanical Property of Blends of Organosolv Lignin Alkyl Esters with Poly(ε-caprolactone)

Abstract

Organosolv lignin (OSL) alkyl esters (carbon number n, 2-5) were synthesized by homogeneous reaction with different acyl anhydrides/4-dimethylamino pyridine in pyridine solution. Miscibility of the esterified OSL with poly("-caprolactone) (PCL) was investigated through DSC, morphological observation, and spectroscopy. DSC revealed a composition-dependent shift in T g for blends of OSL esters (n ¼ 3{5) with PCL; thus these three systems can be regarded as miscible on a T g -detection scale. AFM indicated that no remarkable phase separation occurred in these blends. In observations of crystallization behavior of the PCL component, the OSL derivatives of n ¼ 4 and 5, the alkyl ester substituents of which make a higher similarity in chemical structure with a repeating unit of PCL, exhibited a higher level of miscibility with the aliphatic polyester, compared to the other OSL derivative of n ¼ 3. Thermal-molded blend sheets of OSL esters of n ¼ 3{5 with PCL attained !500% of elongation at rupture at 20 C even when the blends contained 50 wt % of the respective esterified lignin components, reflecting the good miscibility of these OSL esters with PCL.KEY WORDS: Organosolv Lignin / Alkyl Ester / Poly("-caprolactone) / Blends / Miscibility / Glass Transition / Isothermal Crystallization / Currently, studies on bioethanol production from lignocellulosics are being actively pursued.1-4 Irrespective of the bioethanol manufacturing process, lignin is inevitably produced as a consequence of the saccharification of the cellulosic components of lignocellulosics. Although the lignin by-product is considered merely as a heat resource for the process in the present circumstances, its effective application will contribute to cost reduction of the total system for biofuel production.Generally, however, the utilization of lignin as a solid material is constrained by poor film formability and less thermal moldability due to its molecular architecture and intermolecular interactions in itself. Upon heating, lignin molecules decompose rather than soften and flow. In order to alter lignin's viscoelastic properties, considerable efforts have been conducted to employ lignin components either as extenders in polyurethanes, phenol-formaldehyde resins, epoxies, and acrylics, or as grafting backbones for the attachment of other synthetic polymer chains. 5Meanwhile, the importance of polymer blends is now well established as an alternative method of developing completely novel polymers. Furthermore, polymer blending can offer opportunities to modify the thermal and other physical properties of the target polymers. However, it is generally difficult to prepare miscible blends due to the small contribution of the mixing entropy and therefore, in most cases, certain attractive intermolecular interactions between the component polymers should be adopted in order to attain the miscibility or practically good compatibility. Lignin blends or other combinations with synthetic polymers have been investigated many times over the last three decades 6-8 f...

Thermal properties of lignin in copolymers, blends, and composites: a review

“…Among various lignin derivatives blends of lignin esters with synthetic polymers have been extensively studied. 161 It can thus be concluded that the miscibility improves with an increase in the chain length of the ester group. 161 The blends of OSL acetate (OSL-Ac), propionate (OSL-Pr), butyrate (OSL-Bu) and valerate (OSL-Va) have been examined.…”

“…161 The blends of OSL acetate (OSL-Ac), propionate (OSL-Pr), butyrate (OSL-Bu) and valerate (OSL-Va) have been examined. Among various lignin derivatives blends of lignin esters with synthetic polymers have been extensively studied.…”

“…Fully substituted OSL esters can form miscible blends with PCL with miscibility strongly depending on the number of carbons present in the ester side chain. 161 Overall, blending of lignin with synthetic polymers provides a powerful and convenient pathway to generate new materials with improved property/cost performance. 161 DSC thermograms showed that the OSL-Ac/PCL system was not particularly miscible, with the blend being immiscible when the amount of OSL-Ac was increased to 50% (w/w).…”

Thermo‐mechanical characterization of bioblends from polylactide and poly(butylene adipate‐co‐terephthalate) and lignin

“…Kubo and Kadla reported a blend of poly(ethylene oxide) with OL which showed good thermal and mechanical properties, resulting from the unique chemical structure of lignin. Teramoto et al reported a blend of poly(ε‐caprolactone) with alkylated OL which exhibited a miscible blend when the length of the alkyl chains attached to OL increased.…”

Natural Polymers from Biomass Resources as Feedstocks for Thermoplastic Materials

“…Several studies have blended lignin derivatives with other thermoplastic polymers. Different lignin alkyl esters were blended with thermoplastic CAB, PCL, PVAc, and PVP, mainly resulting in multiphase systems. However, thermal analysis showed good miscibility with PVP and PCL, naturally differing with derivative type.…”