Yucheng Peng

Date of Award

12-2013

Level of Access Assigned by Author

Campus-Only Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Forest Resources

Advisor

Douglas Gardner

Second Committee Member

Yousoo Han

Third Committee Member

Stephen M. Shaler

Abstract

Cellulose nanofibrils (CNFs), as a new generation of nano-scale materials from forest products, have attracted considerable attention. They are generally processed as aqueous suspensions, limiting their utilization in reinforcing non polar thermoplastics. The overall goal of this dissertation was to develop bench-scale processing technology to dry CNF suspensions and utilize the dried CNFs in non polar thermoplastics. This is subdivided into: 1) developing a drying process technology for CNF suspensions, 2) characterizing the dried CNFs, and 3) developing CNF reinforced non polar thermoplastic composites on the bench scale using an extrusion process.

Five methods were examined to dry CNF suspensions, including nanofibrillated cellulose (NFC) and cellulose nanocrystals (CNCs): (1) air-drying, (2) oven-drying, (3) freeze-drying (FD), (4) supercritical-drying (SCD), and (5) spray-drying (SD). After drying, the morphology and particle size distribution were characterized by scanning electron microscopy (SEM) and a morphological analyzer. Air-drying and oven-drying formed similar bulk materials and were deemed to be inappropriate for drying CNFs. SCD preserved the nano-scale dimensions of the CNFs with highly-networked structures. FD formed ribbon-like structures with nano-scale thicknesses. SD formed particles with a size distribution ranging from nanometer to several microns and is proposed as a suitable drying method in this study. The effect of four drying methods (AD, FD, SCD, and SD) on the thermal stability, crystallinity, and surface energy of the CNFs were also characterized using thermogravimetric analysis (TGA), X-Ray diffraction (XRD), and inverse gas chromatography (IGC).

Following the previous studies, spray-drying process was investigated by exploring the effect of three spray-drying process parameters on the particle size and morphology of NFCs and CNCs: (1) the gas flow rate, (2) the liquid feed rate, and (3) the suspension solids concentration.

Spray-dried NFCs have been used to reinforce non polar thermoplastic. The manufacture of spray-dried NFCs reinforced polypropylene (PP) composites was conducted using a twin-screw co-rotating extruder. Treatment of the NFCs using maleic anhydride grafted polypropylene was performed. The research results indicate that the mechanical properties including flexure, tension, and impact were improved with the reinforcement of the spray-dried NFCs. Uniformly distributed NFCs in PP was observed on the impact fracture surfaces using scanning electron microscopy.

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