Characterization of cellulose nanofibrils (CNF)

Transcription

1 Characterization of cellulose nanofibrils (CNF) Ali Naderi Tel: +46-(0)

2 Cellulose nanofibril (CNF) Length several micrometers Width 100 nanometers

3 Cellulose nanofibril CNFs Broad size distribution Highly entangled

4 Cellulose nanofibril CNFs Entangled state vey difficult to separate the different constituents Properties are defined by all the different constituents Innventia s characterization strategy Investigation of the overall properties Combination of different methods All methods have their strengths and weaknesses!

5 Characterization: Why? Evaluation of the impact of different processing conditions on (selected) properties of CNF Important for the development of CNF-related processes Quality control

6 Characterization Requirements Easy to employ Simple methodology, affordable machinery, high reproducibility, quick Logical responses and trends in the results Good correlation with other methods of analysis

7 Innventia s current methods of analysis Rheology Higher rheological response (often) indicates higher degree of fibrillation Mechanical properties of CNF-film Higher strength indicates higher degree of fibrillation Centrifugation A higher concentration in the supernatant (often) indicates higher degree of fibrillation Barrier properties of CNF-films Highly fibrillated CNFs (often) have excellent barrier properties, compared to less fibrillated systems

8 Rheological studies

9 Rheological investigations Established method in the industry Polymer industry Food industry Highly sensitive Advantage Detection of small changes Challenge Development of rigorous sample handling- and measuring protocols

10 Rheometer Imposes a specific deformation to the sample, and monitors the resulting deformation

11 Rheological test methods Controlled shear rate measurements Creep tests Relaxation tests Oscillatory Measurements. Oscillatory strain sweep (increasing the applied strain at constant frequency) Oscillatory frequency sweep (the applied strain is kept constant while the frequency is increased)

12 Controlled shear rate measurements What we do? Apply a deformation at a fixed speed = shear rate (γ ) What we measure? Stress ( ) Viscosity * ( ) = γ * Apparent values!

13 Oscillatory measurements What do we do Apply a oscillatory deformation strain/force What do we register The elastic response of the viscoelastic material (storage modulus, G ) The viscous response of the viscoelastic material (loss modulus, G )

14 What do G and G tell? When we have a flowing material like dilute polymer solutions: G < G When elastic properties dominates (e.g. nanocellulose gels): G > G Information that can be obtained: Increasing degree of delamination increasing G Very strong gels: G G 10 G

15 Rheological studies at Innventia Sampling Sample handling Choosing the correct geometry Measuring

16 Sampling The sample is collected straight from the homogenizer/microfluidizer, to avoid: Contamination Change of the dry content

17 Sample handling Equilibration of samples 3 days Storage in fridge Equilibration of samples at room temperature 24 hours

18 Geometry Measuring geometry Plate-cone Plate-plate Cup and bob Smooth surfaces Splined surfaces to minimize slip effects Used when G G

19 Measuring protocol Shaking the sample container or blending the content to even out the sample Employing equal amounts of sample in the measuring chamber (increases the reproducibility) Pre-shearing of the sample in the measuring chamber to even out the sample Covering the chamber with a hood to decrease water evaporation Equilibration of the sample before measuring

20 Mechanical properties of CNF-film

21 Mechanical properties of CNF-film Tensile strength measurements on sheets is an established method in the pulp & paper industry Description: Dewatering of the CNF suspension through filtration Drying of the CNF-films in constrained form Analysis

22 CNF-film preparation: General description Preparation of diluted CNF suspensions Dilution of concentrated CNF samples to 0.1% (w/w) Blending process: magnetic stirrer (750 rpm/min, 24 hours) Production of CNF-films through filtration Degassing of the 0.1% (w/w) samples by applying vacuum Careful addition of the sample (along a glass rod) into the filtration unit Application of vacuum to remove the excess water

23 CNF-film preparation: General description The filter-membrane and the film are dried in constrained form 50 C/ 7 hours a) b) c)

24 Tensile strength measurements Width: 6 mm Length: 45 mm Distance between the grips: 30 mm

25 Centrifugation

26 Centrifugation Basis Centrifugation of highly diluted (<< 1% (w/w)) CNF systems Easier separation of particles* Smaller particles can better resist the centrifugal forces (compared to larger particles) * Naderi et al. 2014) Cellulose, 21(4),

27 Protocol 0.02% (w/w) CNF samples are prepared (magnetic stirrer, 750 rpm/24 h) Centrifugation: 1000g for 15 minutes The suspension concentrations before (c bc ) and after (c ac ) the centrifugation treatment are used to estimate the fraction of nano-sized cellulosic materials (c NS (w/w) %) in the dry content of the suspension: c NS % (w/w) = c ac c bc x

28 Barrier properties OTR (oxygen transmission rate) is the steady state rate at which oxygen gas permeates through a film at specified conditions of temperature and relative humidity. Standard test conditions: 23 C 50% RH or 23 C and 80% RH. Courtesy of Göran Flodberg (Innventia)

29 Comparison of the properties of different CNFs

30 CNF systems Carboxymethylated CNF (CNF Carb ) Charge density: 30 eq/g Enzymatically pre-treated CNF (CNF Enz ) Charge density: 600 eq/g CMC*-grafted CNF (CNF CMC ) Charge density: 170 eq/g * Carboxymethyl cellulose

31 Viscosity (Pa.s) Rheology Nr of homogenization passes in the CNF manufacturing process: 1 or CNF Enz 1pass CNF Enz 5 pass CNF Carb 1 pass CNF Carb 5 pass CNF CMC 1 pass CNF CMC 5 pass Gen1 1 pass Gen1 5 pass Gen2 1 pass Gen2 5 pass Gen4 1 pass 8 Gen4 5 pass Dry content: % (w/w) a) 500 Highest viscosity for CNF Carb Little change in viscosity of CNF Enz The CNF is difficult to fibrillate! Dry content % (w/w)

32 Apparent fraction of nano-sized material (c NS ) c NS (%) 1.9% (w/w) Gen1, 1 pass 3 1.9% (w/w) Gen1, 5 pass 5 2.0% (w/w) Gen2, 1 pass % (w/w) Gen4, 1 pass % (w/w) Gen4, 5 pass 24 Highest c NS for CNF Carb Increasing nr of passes leads to little change in the c NS of CNF Enz

33 Tensile strength measurements on CNF films Tensile strength index (TSI) (knm/kg) TSI of CNF Enz is little affected by EC Highest TSI for CNF Carb TSI of CNF CMC increases with EC 1.9% (w/w) CNF Enz, 1 pass 1.9% (w/w) CNF Enz, 5 pass 2.0% (w/w) CNF Carb, 1 pass 2.0% (w/w) CNF CMC, 1 pass 2.0% (w/w) CNF CMC, 5 pass

34 Barrier properties: Oxygen permeability (OP) Poor barrier properties for CNF CMC Better barrier properties for CNF Enz than CNF Carb, at 50% RH?! Similar properties for CNF Enz and CNF Carb at 80% RH OP** (23 C/50% RH) OP** (23 C/80% RH) (cm 3 μmm 2 d 1 kpa 1 ) (cm 3 μmm 2 d 1 kpa 1 ) 1.9% (w/w) CNF Enz, 1 pass % (w/w) CNF Carb, 1 pass % (w/w) CNF CMC, 1 pass * * Not measured ** OTR normalized with the film-thickness

35 CNFs Exciting properties/exciting applications

36 Stiffness comparable to Kevlar* Strength comparable to glass fibre** * Sakurada et al. (1962) J. Poly. Sci. 57, ** Saito et al. (2012) Biomacromolecules 14,

37 Spinning of CNF threads Patented technology (by Innventia and KTH) Karl Håkansson (2014) Nature Communications,

38 Exciting properties Nano-sized material Dry strength additive in pulp and paper applications Stronger paper and cardboard products CNF Innventia AB (unpublished results)

39 Viscosity (Pa.s) Network formation (percolation) at vey low concentrations (< 1% (w/w)) Rheological modifiers Composite applications ,1 0,01 0,001 0,01 0, Shear rate (s -1 ) Amount of CNF in a polymer-composite Boufi et al. (2013) Macromol. Mater. Eng. 299(5)

40 Low thermal expansion coefficient* Electronics * Fukuzumi et al. (2009) Biomacromolecules 10 (1), CNF-film** ** Siro et al. (2011) J. Appl. Poly. Sci. 119 (5),

41 Excellent barrier properties Dense films (same density as crystalline cellulose 1.5 g/cm 3 ) Packaging applications

42 High surface area ( 300 m 2 /g) and high strength Foams and aerogels > 90 (vol)% porosity Expanded polystyrene

43 NFC AEROGEL DEVICE Hamedi et al., Angew. Chem Supercapacitor of crosslinked NFC aerogel coated with PEI and SWCNT, (PEI/SWCNT)

44 Innventia s CNF: potential applications NFC Carb Transparent films Rheological modifiers Barrier applications Threads Foams Conducting materials NFC Enz Barrier applications Dry strength additive NFC CMC Dry strength addtive

45 Thank you for your attention!