innovhub-ssi, paper division, milano, italy · bpk paper samples rod-coated with tio 2 /nfc...
TRANSCRIPT
8th June 2015, Valencia, Spain
INNOVHUB-SSI, Paper Division, Milano, Italy
www.innovhub-ssi.it
Studies on the antibacterial effect of TiO2 NPs coated paper
Influence of the storage conditions
Hydrophilic vs. Hydrophobic paper
Development of photo-active TiO2/NFC coating formulations
Direct Mixture vs. LbL approach
Antibacterial activity
Industrial Pilot trial at Multipackaging Solutions (UK)
Development of an active overprint varnish formulation
Antibacterial assessment of paper-based packaging with ZnO active nanoparticles
Considerations on the impact on End of Life options
Biodegradability
Recyclability
Outline
2
Typical semiconductor, creates holes and electrons by light irradiation with higher energy
than TiO2's band gap energy (wave length < 380nm).
Solar radiation: only 5% radiation in the UV range.
Advantages
Decomposition and elimination of organic compounds (e.g. NOx, ethylene)
Possible inactivation of bacteria and moulds.
Disadvantage
Potencial oxidative degradation of cellulose and subsequent cleavage of polymer
chain.
TiO2NPs Mechanism
Ngo et al, Interface
Science 163 (2011) 23–38
3
Methodology
4
TiO2 Water
suspension
Functionalization of the paper surface with TiO2 NPs
Dip-coating: physical adsorption of inorganic nanoparticles
Rod-coating: previous inclusion of nanoparticles in the NFC
TiO2 photoactivation
4 h of exposition:
- solar lamp (GE ARC70/UVC/730 - 6000 lux)
Antibacterial activity
Based on AATCC Test Method 100-1998.
TiO2 Water
suspension
Dip-coated
paper
Paper
sample
Sample Grammage
(g.m-2)
Cobb60
(H2O.m-2)
BK 120 74.45
BPK 300 8.42
Studies on the antibacterial effect of TiO2 NPs coated paper
Bleached Kraft paper - BK
0
1
2
3
4
5
6
7
8
0 0.2 0.8
log
CF
U T
24
TiO2 retained on paper, g/m2
log CFU T0
S. aureus log To = 5.6
Sample R
BK1 4.1
BK2 5.5
Reference - BK
5
0
1
2
3
4
5
6
7
8
9
1 week indoor-light 1 week dark 3 weeks indoor-light 3 weeks dark
log
CF
U T
24
Reference 0.2g TiO2 0.8g TiO2
Antibacterial activity: Influence of the storage conditions
Influence of the storage conditions over time: Indoor-light vs. dark
1 week
Bactericidal effect for both indoor-light and dark conditions.
3 weeks:
The bactericidal effect continues and is independently of the storage conditions.
log CFU T0
6
Antibacterial activity: Hydrophilic vs. Hydrophobic paper
Bleached Kraft paper (BK) versus Bleached pre-coated Kraft paper (BPK)
S. aureus log To = 5.6
Sample R
BK1 4.1
BK2 5.5
BPK1 0
BPK2 0
BPK - Drawbacks
Lower Cobb 60 – hydrophobic paper
Non-homogenous coating
0
1
2
3
4
5
6
7
8
9
0 0.2 0.8 0 0.15 0.20
log
CF
U T
24
% TiO2
BK BPK
7
Advances in the use of NFC as a binder for rod-coating formulations
NFC – nanofibrillated cellulose
Negatively charged surface
NPs suspension
Initial conditions: 6%TiO2, pH = 1
Positively charged
Electrostatic behaviour of the NPs suspension
Development of photo active TiO2 /NFC coatings
-40
-30
-20
-10
0
10
20
30
40
0 2 4 6 8 10 12 14
Zeta
po
ten
tia
l (m
V)
pH
TiO2 NPs suspension is stable only at
positive charge.
pH(I)
8
Direct mixture
Deposition of inorganic nanoparticles onto the NFC fibres surface
TiO2 /NFC coating formulations
IDEA: Increase the retention of NPs on NFC
Layer-by-layer assembly - LbL approach
By modification of NFC:
1. Polycation solution (PDDA)
2. Polyanion solution (PSS)
Increasing the negative charge of NFC
9
Direct Mixture vs. LbL approach: retention efficiency
Relation on the %TiO2 retention by NFC
DM formulations: just 25% of retention efficiency;
PE type formulations presents a better efficiency for higher quantities of TiO2 added to NFC;
PE-3 layers shows the highest electrostatic interaction with a maximum of 90% of NPs
grafted onto NFC.
10
0
10
20
30
40
50
60
70
80
0 10 20 30 40
TiO
2 a
dd
ed
on
to N
FC
(g
/10
0g
)
TiO2 retained on NFC (g/100g)
DM formulations
PE formulations
PE - 2 layers
PE - 3 layers
0
10
20
30
40
50
60
70
80
0 10 20 30 40
TiO
2 a
dd
ed
on
to N
FC
(g
/10
0g
)
TiO2 retained on NFC (g/100g)
DM formulations
PE formulations
P1 DM
1
NFC
BPK paper samples rod-coated with TiO2 /NFC coating formulations
Inhibition to bacterial growth (≈ 2 log bacterial reduction) is verified on paper surfaces with 0.7 g
of TiO2 NPs per square meter;
Antibacterial effect increases for higher concentrated samples.
Antibacterial activity
S. aureus log To = 5.6
Sample R
0.7 g TiO2 1.8
4.1 g TiO2 2.7
Bacteriostatic effect
✔ Possibility to develop contact active surfaces
11
Industrial Pilot trial at Multipackaging Solutions
Development of an active overprint varnish formulation based on ZnO nanoparticles
flexography printing
Target
Medical packaging to prevent cross contamination
in hospitals
12
Development of the overprint varnish
Industrial trial – considerations
Inorganic nanoparticles were chosen due to their commercial availability and good compatibility
with industrial needs (e.g. absence of odour);
TiO2 was not compatible with the commercial varnish used at the industrial installation;
ZnO was found compatible with the commercial varnish and had the advantage of being less
sensitive to photo activation (dual antibacterial mechanism).
13
Relatively good viscosity behaviour when up to 10%
of the varnish was replaced by ZnO formulation.
0
50
100
150
200
250
0 100 200 300 400 500 600 700
Vis
co
sit
y (
mP
a)
Strain Rate (s-1)
C1 C2 ZnO formulation C3 C4
Antibacterial activity
Paper-based medical packaging with ZnO active nanoparticles - MPK
Promising results for packaging with higher amounts of ZnO NPs
S. aureus log To = 5.8
Sample R
5.6 mg 0.7
238.3 mg 1.6
504.0 mg 2.9
1512 mg 3.8
Poor bacteriostatic effect (R<1)
0
1
2
3
4
5
6
7
8
0.0 5.6 238.3 504.0 1512.0
log C
FU
T2
4
ZnO on paper, mg/m2
S. aureus log To = 5.8
Sample R
5.6 mg 0.7
Bactericidal effect
On the other hand!
14
Considerations on the impact on End of Life options
Biodegradability
Recyclability
15
30
35
40
45
20 25 30 35 40 45 50 55
Bio
de
gra
da
bil
ity (
%)
Time (days)
Paper Reference MPK MPK+ZnO NPs
Biodegradability
Does the nanoparticles affects the Biodegradability??
NO SIGNIFICANT DIFFERENCES between treated papers and reference!
16
0
5
10
15
20
25
30
35
40
45
0 5 10 15 20 25 30 35 40 45 50 55
Bio
de
gra
da
bil
ity (
%)
Time (days)
Paper Reference MPK MPK+ZnO NPs
Tested according to EN13432 standard
Does the nanoparticles affects the Biodegradability??
0
20
40
60
80
100
0 5 10 15 20 25 30 35
Bio
deg
rad
ab
ilit
y (
%)
Time (days)
Reference 1% TiO2 (w/w) 10% ZnO (w/w)
Biodegradability
Slightly delay for ZnO paper samples, maybe function of:
Concentration of NPs
Type of NPs
Very likely both samples will reach the required 90% pass-level in the end of the experiment.
17
60
days
Recyclability of active packaging material
Test carried out on kraft paper functionalized with TiO2 NPs based on
Aticelca method MC 501-13
To understand where the nanoparticles goes!
To the water stream, or
Retained in the fibres?
> 99% of TiO2 NPs retention on the fibres, after one cycle.
18
Conclusions
Photoactive TiO2 nanoparticles can be directly deposited on hydrophilic bleached Kraft
paper achieving strong antibacterial contact active surfaces;
The bactericidal effect last several weeks after activation, under light or dark conditions;
TiO2/NFC based coatings formulations can be used for hydrophobic paper samples.
They can be developed by direct mixing, however polyelectrolyte-assisted deposition by
LBL assembly is a good option to increase retention (90% retention efficiency against
25%);
The industrial trial performed with an active overprint varnish formulation based on ZnO
nanoparticles showed a relatively poor inhibitory effect;
Future work will focus on finding suitable varnish components thus increasing ZnO
concentration.
Packaging End of Life options
Laboratory tests showed only marginal effect of active ingredients on biodegradability
performance.
Recyclability tests proves a very good retention of TiO2 nanoparticles in the fibres;
After one recyclability cycle there is not migration of the NPs to the water stream;
19
Outreach activities
20
Oral presentations:
European Paper Week 2013, Brussels, Belgium, November 26-28, 2013,
Antibacterial photo-active TiO2 dip-coated paper.
ICNF2015, 2nd International Conference on Natural Fibers, Azores, Portugal, April 27-29, 2015,
Antibacterial coating formulations based on NFC and photo-active TiO2 nanoparticles.
Aticelca, 46th Annual Congress of the Italian Paper Industry, Sestri Levante, Italy, May 28-29, 2015,
Development of Antibacterial Papers by Incorporation of Active Nanoparticles.
Poster Presentations:
NanotechItaly 2013 International Conference, Venice, Italy, November 27-29, 2013,
Photoactive titanium dioxide for paper based packaging applications.
Joint Conference PTS/COST FP 1003 On Innovative Packaging, Munich, Germany, May 20-21,
2014,
Contact active materials for developing innovative antimicrobial paper based packaging.
IFIB 2013 - 3rd Italian Forum on Industrial Biotechnology and Bioeconomy, Naples, Italy, October
22-23, 2013, Antibacterial activity of TiO2 on dip-coated papers for food contact packaging applications.
Secondments:
CBIMO, West Pomeranian University of Technology, Szczecin, Poland, July 2013; Encapsulation
techniques suitable for paper based coatings applications;
CICECO, University of Aveiro, Aveiro, Portugal, November, 2014, Development of suitable coating
formulations by Layer by Layer Assembly for functionalize paper surfaces.
