Super-hydrophobicity on Paper Surface by Utilizing Nanocomposites: Fabrication

and Application

Speaker: Xue Zhang

PhD Candidature, Interface Science & Surface Engineering Research GroupBAMI, Department of Chemical Engineering

Monash UniversityEmail: xue.zhang@monash.edu

Liquid packaging materials (LPM)

Proposed application of super-hydrophobic surface

Conventional Method:1. Base sheet2. Laminating Aluminum3. synthetic organic polymers

Potential technology direction:1. Base sheet2. Super-hydrophobic coating (inorganic fillers; cellulose nanofibers; wax)

Drawbacks:� cost expensive process� Hard to recycle� environment disposal issue of Al and plastics� Adhesion problem

Strengths� Simple and cost-effective process� Easy to recycle� Reduce adhesion

Super-hydrophobic Liquid packaging materials(SH-LPM)

Introduction� What is super-hydrophobic (SH) surface ?

Contact angle ≥ 150˚ Tilt angle < 5˚

� How to fabricate super-hydrophobic surface?

Inspiration from nature

Lotus effect

Observation:� Low surface energy

(waxy knob)� Micron and nano scale (dual-scale)

roughness

Current techniques� Lithography techniques� Electrospinning� Plasma etching� Layer-by-layer (LBL) method� Phase separation� Templating process� Sol-gel technique� Deposition method (Chemical vapor deposition; Electroless galvanic deposition;

Electrochemical deposition; spin coating/dip coating/spray coating; self-assembly process)� ……

Challenges:�Lab-scale technique�Complicated procedure�High-cost

Introduction

Our strategy

o Step 1: Build up surface with dual scale roughness using nanocomposites (inorganic fillers and cellulose nanofibers).

o Step 2: Treat the textured surface with wax.

Cellulose nanofibers (CNF)

MaterialsTwo-step dip coating

Nano precipitated calcium carbonate(PCC) Nano ground calcium carbonate(GCC)

Nano Montmorillonite OR Nanoclay (MTM)

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SEM images of the coated

surfaces

(c)

(a) (b)

162.4 3.3˚

(d)

Nano Montmorillonite (MTM) modified SH surface (NMSH)

Nano GCC/MTM modified SH surface (NGMSH)

Nano MTM/PCC modified SH surface (NPMSH)

Nano precipitated calcium carbonate (PCC) modified SH surface(NPSH)

Nano ground calcium carbonate (GCC) modified SH surface (NGSH)

151.4 3.1˚

(e)

Challenges of SH surface using in liquid packaging materials

Service conditions Super-hydrophobic surface Liquid packaging materials

Service objects water fruit juice; tea; milk; sugar- and honey-containing beverages…...

Objects formation Droplet Bulk liquid

Service pressure No Hydrostatic pressure

Barrier requirement No Yes

Food safety requirement No Yes

The differences of SH surface (based on current characterization method) and liquid packaging materials in real service conditions

� Modify of characterization method of SH surface in order to meet the real service conditions of LPM

� The barrier requirement of LPM was mainly focused in this presentation.

Properties of SH surfaces evaluated for vapour resistancein humid conditions

Performance in humid conditions

In humid conditions (22 1 , 95% RH), apparent contact angle of varying surfaces as function of exposure time.

� AKD sizing alone could not resist water vapor to pass through.� The nano-MTM coating layer was good at resisting water vapor invasion.� PCC particles gave better performance in withstanding water vapor invasion than GCC.� Good moisture resistance are related to the barrier property of the materials, while lack of relation with the super-hydrophobicity.

Average water vapour permeability ( 10-14 kg·m-1·s-1·Pa-1) for varying surfaces

Water vapour permeability (WVP)

The average water vapour permeability ( 10-14 kg·m-1·s-1·Pa-1) for the varying paperboards before and after modified by NPSH coating layer.

Properties of SH surfaces evaluated for vapour resistance in humid conditions

NPSH coating layer applied onto paperboard

� The WVP was increased with the increased of the basis weight of the paperboards, and the trend was the same after thepaperboards were modified by the NPSH coating layer.

� The SH surface could also help to resist moisture transmission.� The NPSH coating layer could get better improvement of WVP on relatively more moisture absorption materials.

Mayer-rod coating method

Viscosity : Carboxymethylcellulose sodium (CMC)By tailoring the average molecular weight and dosage of CMC

Proposed mechanisms for failing to resist vapor attack of SH

sample under humid conditions

ESEM images of (a) dried top surface of SH sample; (b) corresponding hydrated top surface

of SH sample; (c) dried cross-section of SH sample; (d) corresponding hydrated cross-

section of SH sample.

� The nanocomposites coating layer structure became loose and unstable (red circle).� The pore size formed by inter-fibres became smaller due to the dimensional changes of fibres caused by the swollen effect during the moisture absorption process (green and purple circle).� The swelling paper fibres (yellow circle) could further loosen and unstabilize nanocomposites coating layer.

e

Conclusions

� In humid conditions, the super-hydrophobicity of the SH surface with poor barrier property would temporary lossand the performance of SH surface in vapor resistance highly depended on the barrier property of the SH surface.

� The mechanisms for failing to resist water attack of NPSH sample under humid conditions was analyzed by FEIQuanta 3D ESEM system. The main reason for that is the changes of the nanocomposites layer caused by theswollen of paper fiber exposed to high humidity.

� The service time of the super-hydrophobic surface in paper-based liquid packaging materials is limited by themoisture-sensitive property of the paper fiber. Super-hydrophobic surface could be included into the engineeringdesign of liquid packaging materials to reduce the adhesion problem.

BAMI

AAny Questions ?

Thank you!