Control of the barrier properties of PLA by means of ... · Ester content in plasma and film . Evolution of ester contents are similar in plasma and film as a function of power

Sylvie Ligot (1,2), Philippe Dubois (2,3) , Rony Snyders (1,3)

(1) Chemistry of plasma surface interactions, CIRMAP, UMONS - 20, place du parc, B-7000 Mons, BELGIUM (2) Laboratory of Polymeric and Composite Materials, CIRMAP, UMONS - 20, place du parc, B-7000 Mons, BELGIUM (3) MateriaNova Research Center- Parc initialis, 1, Avenue Copernic, B-7000 Mons, BELGIUM

Control of the barrier properties of PLA by means of biobased plasma

polymer coatings

[email protected]

Université de Mons AIMCAL Europe conference 2014– Cascais, June 9-11| Sylvie Ligot

Content Plasma technology in Mons

Context & strategy of the project

Plasma polymers development

Thin films characteristic Plasma diagnostic

Barrier property

Conclusions

2






Barrier property

Conclusions

3

Université de Mons 4

Our framework…

AIMCAL Europe conference 2014– Cascais, June 9-11| Sylvie Ligot


University of Mons

• One of the five French speaking Belgian universities

• 7 faculties and 5000 students

• 500 researchers and scientists

• Founded by UMONS in 1995

• Dedicated to the design of new materials (thin films, polymers, composites)

• Financing scheme: 60% from competitive projects, 40% from the industry

• ~100 researchers

Materia Nova R&D Center



Research philosophy @ ChIPS

Our objective is to contribute towards the understanding of the plasma-surface interactions during the treatments of materials







Barrier property

Conclusions

7

Université de Mons

In order to use PLA in the packaging industry, it is necessary to decrease the diffusion phenomena through the material:

• By modifying the bulk polymer : increase the cristallinity and use of nanoparticles &

• By using barrier coatings : deposit a high cross-linked organic thin film

8

[1]

[1] : P. juliano et al. Food Eng. Rev (2010) 2:274

FDA requirement

hydrolyse of ester bonds

Context

polylactic acid (PLA) is a good candidate

Plastic packaging (food, electronic,…) Bio based and biodegradable polymers

But… important gases permeability

Control of the degradation rate



Scientific Strategy

Bulk Treatment : addition of layered silicate clays & crystalliser

Cloisite 30B :

Surface Treatment : barrier coating by of plasma polymer film

EBS :

Conventional PLA

Nanocomposite PLA/CL30B/EBS

Plasma polymer coating on PLA/CL30B/EBS

Coating by PECVD : biobased, biodegradable and barrier plasma polymer film

1

2



Experimental strategy 1. UMONS : Fundamental research using a lab-scale system in order to get a better

understanding of the plasma polymerization process

10 AIMCAL Europe conference 2014– Cascais, June 9-11| Sylvie Ligot

o Si wafers

o Film characterization • Ex-situ XPS + chemical

derivatization • Ex-situ ToF-SIMS + PCA

o Plasma diagnostic

• Mass spectrometry • In situ FTIR spectroscopy

Mass spectro

Gold mirrors under vacuum

In situ FTIR

Gold mirrors under vacuum

• Multi-reflexion : 13 mirrors • 26 passes • Resolution max : 0.09 cm-1 • Min detected pressure : 0,3 mTorr

Université de Mons

Experimental strategy

11

2. MATERIANOVA : Transfer the knowledge on a semi-industrial scale (R2R PECVD system)


I. Cleaning and functionalization of substrate (DBD) II. Deposition of barrier coating by PECVD

Roller width = 36 cm / Speed of coils = 0,01 to 3 m min-1 / Substrate thickness = 200 µm

Adhesion

DBD (1-100 Torr)

PECVD (10-100 mTorr)

I

II






Barrier property

Conclusions

12

Université de Mons

Plasma polymer films as barrier coatings

13

• Crosslinking degree of the plasma polymer

• Chemical composition in the plasma polymer

Which plasma polymer?

Chemical precursor? Ethyl lactate

“PLA-based” plasma polymer because (i) (bio)degradable films, (ii) adhesion on bulk PLA

Degradation rate? Barrier efficiency ?


Coming from lactid acid, ethyl lactate is also biobased !

http://en.wikipedia.org/wiki/File:Ethyl_L-lactate.png

Université de Mons

Plasma polymerisation of ethyl lactate

Plasma Polymer Thin Film Substrate

C4H7O3.

H2O hѴ

C2H4

e-

H.

C5H10O3

C5H9O2 .

C2H5O . C5H9O3

.

HO . CHO2

.

CO2

C2H5O .

C3H7O2 .

Plasma diagnostic

Film characterization

• ESTER DENSITY • Crosslinking degree • Barrier property (OTR measured by Manometric Gas

Permeation Analyser)

Evaluation of the ESTER DENSITY in the plasma phase

Better understanding of plasma-surface interactions

Fine control of the composition and structure of the PPF

14

C2H2

CO


http://upload.wikimedia.org/wikipedia/commons/d/d3/Lactic-acid-skeletal.svg

Université de Mons

Chemical composition of PPF

• C/O ↗ from 2.5 to 10 when PRF ↗

• Ester content ↘ from 18 to 2 % (ester retention from 90 to 10 %)

Fragmentation of ethyl lactate precursor induces a decreasing of ester functions density in the PPF

Does the plasma chemistry support the conclusions drawn from the chemical analysis of

the ppf ? • Mass spectrometry • In situ IR

15

Chemical derivatization of COOH to get COOC

At.% COOC At.% COOH +

C/O ↗ with power : ester content ?



Mass spectrometry

C3H7O2+

CH3O2+

C2H5O+

45

75 47

28

26

C2H4+, CO

C2H2+

No information about the ESTER CONTENT in the plasma phase

The mass spectrometry data support the ppf chemistry evolution as a function of PRF

Complementary diagnostic tool : in situ IR spectroscopy



In situ IR spectroscopy

OH

CHx

ester C-O Good agreement with

literature [1]

Labelling of ethyl lactate peaks

BUT

Plasma ON spectra = generated fragments difficult to identify

Help from theoretical approach (DFT calculations)

Ethyl lactate gas 30 mTorr – PLASMA OFF

[1] Su-E & Chan, spectroscopy letters, 34(3), 371-374 (2001)

[1]

Sylvie Ligot / IVC-19 / Paris, September 9-13, 2013

CH3 CH

OH

C

O

O CH2CH3


DFT : Theoretical vibrational modes

• Calculation of the spring constants (k) for each vibrational mode based on harmonic potential


• Validation of the approach for the precursor

• Ethyl lactate has 18 atoms DFT calculates the 3N-6 = 48 vibrational modes

For each vibrational mode, we get : • Frequency • Relative intensity Synthetic IR spectrum of ethyl lactate

• By DFT, we can observe the vibrational modes Ester stretching ≈ 1750 cm-1 [1]

[1] B. Smith, IR spectral interpretation,CRC Press, London, 1999

Université de Mons

C-O

OH

19

In situ IR supported by DFT This peak can be attributed to [ester] in plasma

ester

CHx


Observation : OH - CHx - ester - C-O

Slight difference between theory and experiment : • FWHM isolate

molecule in DFT

• Position harmonic approximation in DFT

Use this theoretical approach to interpret IR spectra of generated fragments at plasma ON

[1] B. Smith, IR spectral interpretation,CRC Press, London, 1999

OH stretch

Experimental IR

CHx sym & asym stretch + scissor

ester C-C-O stretch

ester C=O stretch

CH-OH stretch

CH-OH scissor

Synthetic IR

DFT is a support for the IR interpretation


C2H4 CO2 CO

C2H2

OH CHx

C-O

C2H2

CO CO2

C2H4

C-O

CHx

OH

In situ IR measurements: Influence of Power

Decrease of ESTER with power

Comparison of the evolution of the ester content in plasma and film with power ?

Ligot et al, submitted to J. Chem B

Pmean increases the fragmentation degree inducing the loss of functional fragments in favor of short and stables molecules

By IR spectroscopy, we observe all ester functions !!!

IR radicals precursorEster Ester Ester= +

Reactive species which contribute to the film

growth

Unreactive species pumped out of the

system

Influence the ester content in film

Influence the ester content in film

BUT


Evolution of the ester content in plasma

According to this, we can do a more representative comparison of the evolutions of the ester contents in plasma and film with power ?

% of undamaged precursor molecules in the plasma phase ( )?

precursorEster


Strong decrease of reactive ester content in plasma when power increases

From the IR plasma spectrum, we subtract the precursor spectrum

Université de Mons

Ester content in plasma and film Evolution of ester

contents are similar in plasma and film as a

function of power

It is possible to tailor the chemistry and structure of ethyl lactate plasma polymer films which could be used as a coating with adaptable barrier properties

22

• Understanding of plasma polymerization process

• Control of the

biodegradation rate through the control of ester density







Barrier property

Conclusions

23

Université de Mons 24 AIMCAL Europe conference 2014– Cascais, June 9-11| Sylvie Ligot

OTR measurements : influence of bulk modification

/2 • Increase of crystallinity from 3 to

12 %

• Good dispersion of nano-clays

The bulk modification increase the barrier property by limiting the diffusion phenomenon

Université de Mons 25 AIMCAL Europe conference 2014– Cascais, June 9-11| Sylvie Ligot

OTR measurements : influence of surface modification

Without coating

Without coating Coating

30 W Coating 280 W

Cross-linking degree ↗

Surface defaults probably due to the stress

Higher is the cross-linking degree, higher is the barrier efficiency, but the coatings have still low influence

on the OTR

~ No influence !

Université de Mons

Conclusions

Understanding and control of the plasma polymer film deposition

• Study of the plasma and film chemistries in terms of ESTER densities for a better understanding of the plasma polymerization process

• Control of the film properties towards the

application of barrier coating with controllable degradation rate

Double the PLA barrier efficiency by bulk and surface modifications


Without coating

Without coating Coating

30 W Coating 280 W

Université de Mons

Thanks you very much for your attention !!

Acknowledgements


Documents

Control of the barrier properties of PLA by means of ... · Ester content in plasma and film . Evolution of ester contents are similar in plasma and film as a function of power