Natural Surfactants for Flotation Deinking in Paper Recycling

R. A. Venditti, O. J. Rojas, H. Morris, J. Tucker, K. Spence, C. Austin and L. G. Castillo

Forest Biomaterials Science and Engineering, North Carolina State University, Raleigh USA

IntroductionThe flotation process necessitates stable foams to allow the separation of ink from fiberFoaming agents may be added to stock at 0.02 to 0.2 % of solidsCurrently, many of the foaming agents are petroleum-based and may not be environmentally friendlyAre there more green alternatives that may lessen dependence on petroleum feedstocks? How to evaluate?

Surfactant at Interfaces:Modification of the surface energy

Water Air or Oil

Interface

Polar Non- Polar

Surfactant

Polar Group

Non-polarGroup

OOHO

OH OH CH

2OH

Surfactant

Detergency

θθ

initial state:no surfactant

change in wetting

Separation by shear (rolling)

substrate

oilwater

substrate

inkwater

+ surfactant:

θθ

θθ

Substrate

oilwater

θθ

θθ

ink

A B

Detergency

Adhesion Destabilization

attra

ctio

nre

puls

ion

Distance

(1) adhered particle(2) particle separation(3) particle removal

substrate

ink

11 surfactant adsorption/diffusion

22 adhesion reduction

33 mechanical shear separation

e

(1)(1)

0

(2)(2)V2

e

E

V

V1

(3)(3)

Surfactant at Air-Water Interface: Foam Stability

liquid film

gas

strained area

low surface tension

surfacetension g

radient

liquid flow

low surface tension

high surface tension

IntroductionThe flotation process is a complex process requiring multiple steps to occur:

Release of the ink from fiberAttachment of ink to air bubbleAir bubble to be incorporated into stable foamFoam to be separated from the liquid phase

A surfactant can impact all of these steps……its effect on flotation can be difficult to interpret

Outline

IntroductionMaterialsResults and Discussion

DetergencyAdsorptionFoamabilityFlotation Deinking

ConclusionsQuestions

Surfactants Studied

Alkyl phenol ethoxylate (APE) Alkyl (C10-C16) mono and oligomeric D- glucopyranose Protein-based surfactant from soybeanCommercially formulated surfactant blend

Recovered Paper Material

Recycled Xeroxcopy Paper of 92 brightness and 30% recycled content Copied with text on both sides of the paper with a xerographic toner Pulped at 3% consistency in TappiDisintegrator

Detergency Analysis

Preparation of films via sublimation of tripalmitin, a fatty acid model of an inkExposed ink surface to surfactant solution with shear in beakerMeasured contact angle of water drop on surface of treated film

Condenser

Vacuum Chamber

Ink Source

GoldWafer

Vacuum

Ink Source

Gold

Detergency AnalysisMilli-Q Water Source

Gold Wafer

Light Source

Measurement / Observation

Preparation of films via sublimation of tripalmitin, a fatty acid model of an inkExposed ink surface to surfactant solution with shear in beakerMeasured contact angle of water drop on surface of treated film 0

10

20

30

40

50

60

70

80

90

0 20 40 60 80 100 120 140 160 180 200 2200

10

20

30

40

50

60

70

80

90

0 20 40 60 80 100 120 140 160 180 200 220

Time (min)

Con

tact

Ang

le (d

egre

es)

Detergency Analysis:

Changes in contact angle after treatment of “printed”surfaces with surfactants, before (solid symbol) and after rinsing with water (washing, open symbols) Surfactants make inks more hydrophilicDifferent response to rinsing: different surface affinity

20

30

40

50

60

70

80

0 50 100Time (min)

Con

tact

ang

le (d

egre

es)

Sugar-based

Synthetic

Protein

Commercial

0 50 100

Sugar-based

APE

Protein

Commercial

Detergency Analysis (Contact Angles):

1735Sugar Based

4240Protein-Based

3050APE

1530Commercial

% Change on Rinsing

% Change on Treatment

SurfactantChanges in contact angle after treatment of “printed” surfaces with surfactants, before (solid symbol) and after rinsing with water (washing, open symbols) Surfactants make inks more hydrophilicDifferent response to rinsing: different surface affinity

% Change Treat = 100%* [CA(no treat) – CA(treat)]/CA(no treat)

% Change Rinse = 100%* [CA(no treat) – CA(treat/rinse)]/CA(no treat)

Quartz Crystal MicrobalancePiezoelectric quartz crystal, sandwiched between a pair of electrodes Measures the resonance frequency and dissipation due to adsorption on surface.9 ng/cm2 sensitivity in water

nfC

nf

fnf

ftm qqqq Δ−=

Δ−=

Δ−=Δ 2

0 02

νρρ

Q-Sense E4 unit

QCM-D ping principle

Frequency change (Δf): related to the mass of the attached film

Disipation (ΔD): related to the viscoelasticity

Qcmddemo.exe

“rigid” film “soft” film

Sensor out

T-loop out

Inlet

Control valve

T-loop

Flow with T-loop – Liquid Transport

Sensorcell

speed(ml/min) 0.25

Pump

Reservoir

QCM: Measurement principleCrystal

A(t)=A0⋅exp(-t/τ)⋅sin(2πft+φ)

D=1/ πfτ

Mathematical representationof the decay curve

Fitting routine; Levenberg-Marquandt’s (Numerical Recipies)

•Decay recording – electronics unit•Decay fitting - PC

Recording SensitivityDrive Amplitude

QCM ResultsSurfactant solution injected around 500 sRinsing with water at about 2500 s Commercial surfactant had lowest affinity to model ink filmProtein had highest affinityKinetics revealed

3.712.4Sugar-based

3.113.6Protein-based

3.012.8Synthetic

11.310.1Commercial

Surfactantreleased (ng)

Amountadsorbed (ng)Type

Dynamic Foamability

400 ml of 0.025 g/L surfactant solutionAir flow of 185 ml/min through air dispersing stoneFoam height recorded vs time

Dynamic Foamability

(0 Ross Miles Foam)

(110)

(42)

(108)

Foam

Hei

ght (

cm)

0

5

10

15

20

0 500 1000

Synthetic

Sugar based

Protein based

Commercial mixture

Time

0

5

10

15

20

Synthetic

Sugar based

Protein based

Commercial mixture

0

5

10

15

20

25

0 20 40 60 80

Removal Efficiency as % of ControlM

ax F

oam

Hei

ght (

cm) Synthetic

Sugar basedProtein BasedCommercialmixture

0

5

10

15

20

25

0 20 40 60 80

SyntheticSugar basedProtein BasedCommercialmixture

0

5

10

15

20

0 500 1000

Synthetic

Sugar based

Protein based

Commercial mixture

0

5

10

15

20

APE

Sugar based

Protein based

Commercial mixture

0

5

10

15

20

25

0 20 40 60 80

SyntheticSugar basedProtein BasedCommercialmixture

0

5

10

15

20

25

0 20 40 60 80

SyntheticSugar basedProtein BasedCommercialmixture

0

5

10

15

20

25

0 20 40 60 80

SyntheticSugar basedProtein BasedCommercialmixture

0

5

10

15

20

25

0 20 40 60 80

APESugar basedProtein BasedCommercialmixture

(42)

(110)

(108)

Flotation Deinking Experiments

Pulping 3% K, 10 min, 50 C, TappiDisintegratorFlotation Wemco Lab Cell, 1% K, RT, stopped when foam production ceased, ranged from 60-210 sImage Analysis, Scanner system, 0.007 mm2 smallest particle size considered

( )% *100Control Sample

Control

PPM PPMRE

PPM−

=

Flotation Results: Efficiency vs surfactant charge

At a given surfactant charge, the removal efficiency correlates with the foamability does not reflect selectivity of separation

Surfactant Added to Flotation Cell

0

10

20

30

40

50

60

70

80

90

100

0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70 0.80 0.90 1.00

Surfactant Charge (% on OD fiber)

Rem

oval

Eff.

(%)

Sugar-based

Commercial mixture

Protein-based

APE

Flotation Results: SelectivitySurfactant Added in Flotation Cell

0

10

20

30

40

50

60

70

80

90

100

50 55 60 65 70 75 80 85 90 95 100

Yield (%)

Rem

oval

Eff.

(%)

Sugar based

Commercial mixture

Protein based

APE

Flotation Results: SelectivityProtein-based surfactant has significantly lower selectivity:

highest adsorption onto model ink (QCM)largest decrease in contact angle on model inkHigher MW, charged material

Indication that the protein-based surfactant sterically stabilizes toner in water

Cationic starch interference of toner agglomeration (Berg and coworkers, 1994; Venditti and coworkers 1999)

Acrylate adhesive anti-deposition on polyester by cationic starch (Venditti and coworkers, 1999)

Surfactant Added in Flotation Cell

0102030405060708090

100

50 55 60 65 70 75 80 85 90 95 100

Yield (%)

Rem

oval

Eff.

(%)

Sugar based

Commercial mixture

Protein based

APE

Conclusions

Methods to distinguish differences in adsorption, desorption and detergency between different surfactants have been demonstratedFoamability has a strong correlation with removal efficiency, independent of yield considerationsSelectivity is related to adsorption, surface modification of toner (contact angle) and steric stabilization of ink particles The surfactant with the sugar moieties had similar flotation removal efficiencies than did synthetic (APE) surfactants

Acknowledgements

NCSU Undergraduate Research Program and EPA People Prosperity and the Planet (P3). Support by University of Guadalajara for visiting research experience of Luis Castillo at NCSU is gratefully acknowledged.

We would also like to acknowledge the assistance of Dr. Xavier Turon with the QCM experiments.