CARBOXYMETHYL CELLULOSE NANOCOMPOSITES YongJae Choi Department of Chemical Engineering and John Simonsen Department of Wood Science & Engineering Oregon State University
Outline I. Introduction II. Materials and Methods III. Result and discussion IV. I. Comparison of cellulose nanocrystals (NCC) to microcrystalline cellulose (MCC) II. Thermal cross-linking Conclusions V. Acknowledgements
Introduction CMC-based hydrogels and films have many applications, from fruit leathers to medical implants, supports for electrocatalysis and pervaporation membranes Biodegradable, biocompatible, non-toxic, renewable natural resource, low cost Using MCC as a filler imparts improved mechanical properties to films and gels What is the effect of reduced particle size?
CMC Synthesis Carboxymethyl cellulose (CMC) Derived from cellulose by carboxymethylation Water soluble polymer Efficient, inexpensive reaction Usually sold as sodium salt
Commercial CMC CMC First prepared in 1918 Commercially produced since 1920 Three key parameters to control properties for various applications Molecular weight Degree of substitution (DS) Distribution of the carboxymethyl group
Commercial CMC Unique features of CMC Soluble in water Viscosity control Excellent dispersion of MCC Forms strong and transparent film Immiscible in oil and organic solvent High absorbent polymeric material
Nanocrystalline Cellulose Stronger than steel and stiffer than aluminum Produced by acid hydrolysis of natural cellulose Break microfibrils into elementary single crystallites
Cellulose Nanocrystal Production Native cellulose Amorphous region Crystalline regions Acid hydrolysis Individual nanocrystals Individual cellulose polymer
NCC Cellulose nanocrystal characterization with TEM Average length = 85 nm Average width = 3 nm Agglomeration due to the attractive force
Thermal Dehydration for Cross-linking Alcohol group of poly(vinyl alcohol) (PVA) and acetic acid group of polyacrylic acid (PAA) are cross-linked under mild heat treatment
Objectives 1. Compare cellulose nanocrystal (NCC) to microcrystal cellulose (MCC) in carboxymethyl cellulose composite film 2. Preliminary investigation of thermal crosslinking between NCC and CMC
Materials and Methods Materials Carboxymethyl cellulose (CMC) M.W = 250,000 D.S = 1.2 Aldrich chemical company Cellulose nanocrystal (NCC) Derived from cotton cellulose Glycerin M.W = 92.10 Plasticizer Fisher Scientific
Methods Cellulose nanocrystal preparation Grind cellulose in Wiley mill with 40 mesh screen Acid hydrolysis at 60 C with 65%(w/w) sulfuric acid for 50 min Centrifugation, decant acid, rinse Ultrasonic irradiation and/or Waring blender Decant Ultrafiltration
Film Formation Dissolve CMC in water Mix with NCC or MCC and glycerin NCC concentration 5% to 30% Glycerin constant at 10% Pour into Petri dish and air dry
Thermal Cross-linking Acid form of CMC is achieved by ion exchange (cationic resin) Mix with NCC Glycerin omitted Ultrasonic irradiation Form in Petri dish Air dry Heat treatment at various temperatures for 3 h under nitrogen gas
Mechanical testing (Sintech) Modulus of rupture (MOR) Modulus of elasticity (MOE) Extension at maximum yield strength Methods
Methods Thermal testing (TGA) Ramp 20 C/min Water dissolution test Soak in water at room temperature Measure weight loss Water vapor transmission rate Film covered jar containing water Measure weight loss with time Hot-dry room (30 C, 25% humidity) Mass flux (J) = Mass change (g) Area (m 2 ) * Time (hr)
CMC/NCC/Glycerin Films 90%CMC/10%Gly 80%CMC/10%NCC/10%Gly
Comparison of Microcrystalline Cellulose (MCC) to CNXL in CMC 10% MCC 10% CNXL 200X optical (crossed polars)
Cross Section of Film 90%CMC/10%Gly 80%CMC/10%NCC/10%Gly
Mechanical properties (MOR) Tensile strength (MPa) 40 35 30 25 20 15 30% increase Control NCC MCC -5 5 15 25 35 % NCC/MCC content
Mechanical properties (MOE) 3 2.8 2.6 2.4 Control NCC MCC 85% increase MOE (GPa) 2.2 2 1.8 1.6 1.4 1.2 1-5 0 5 10 15 20 25 % NCC/MCC content
Extension at failure 1.2 60% increase 1 Extension (mm) 0.8 0.6 0.4 0.2 control NCC MCC 0-5 5 15 25 35 %NCC or %MCC, wt/wt
110 TGA 100 Weight, % original 90 80 70 60 100% NCC 100% CMC 90C 85C5N 80C10N 70C20N 60C30N 50 40 150 200 250 300 350 400 450 Temperature, 0 C
Dynamic Mechanical Analysis 10 9 log (G'/Pa) 8 7 6 90C10G 80C10N10G 70C20N10G 60C30N10G 5 170 180 190 200 210 220 230 240 Temperature ( C)
HEAT TREATMENT 5% NCC in CMC No plasticizer
HEAT TREATMENT Tensile strength, MPa 94 92 90 88 86 84 82 80 78 16% increase MOR MOE Elongation 0 0 20 40 60 80 100 120 140 Heat treatment, 0 C for 3 h, 5% NCC-filled CMC 6 5 4 3 2 1 MOE, GPa or % elongation
Water Dissolution 60 50 Weight loss (%) 40 30 20 120C 100C 80C No heat 10 0-5 15 35 55 75 Water immersion Time (hr)
Water Dissolution 70 Weight loss at 3 days (%) 60 50 40 30 20 10 0 0 20 40 60 80 100 120 140 Thermal treatment temp. (C)
Water Vapor Tranmission Rate film Lid with hole jar water
Water Vapor Transmission Rate 2000 1500 11% reduction WVTR, g/m 2 dy 1000 500 0 control heat treated
Conclusions At low concentration NCC is well dispersed in the composites without observed agglomeration of cellulose NCC improved the mechanical properties (strength, stiffness and elongation) as a reinforcing filler compared to MCC TGA suggests close association between NCC and CMC
Conclusions Cross-linking between CMC and NCC can be obtained by heat treatments Higher degree of cross-linking is achieved at higher temperature Cross-linking composites have improved water resistance Cross-linking appears to reduce water vapor permeability slightly
Acknowledgement This project was supported by a grant from the USDA National Research Initiative Competitive Grants Program