A POLYMERIC CRYSTALLINE PHASE AS
ETHYLENE ABSORPTION AGENT
Alexandra Romina Albunia, Gaetano Guerra, Tiziana Minucci,
Vincenzo Venditto
Dipartimento di Chimica, Università di Salerno, Via Ponte don Melillo,
Fisciano, 84084 - ITALY
VI Convegno Nazionale sulla Scienza e Tecnologia dei Materiali
Perugia, Aula Magna dell'Universita' degli Studi 12 - 15 Giugno 2007
Syndiotactic Polystyrene:
termoplastic molecular sieve
The nanoporous s-PS d form
presents a permanent cavity of
120-160 Å3 per 4 monomer units.
– CH – CH2 – CH – CH2–
Tm= 270°C
Fast crystallization (Xc=30 – 60%)
Complex polymorphic behavior
(5 crystalline forms)
It is able to absorb rapidly and
selectively molecules already at
low concentration.
Syndiotactic Polystyrene:
aerogels
Gel
sPS/toluene
2/98 g/g
=0.865 g/ml
S-PS fibrils presenting the nanoporous d phase
diameters of the fibrils 40-70 nm
Solvent removal from s-PS
gel by supercritical CO2
Aerogel
d sPS
=0.023 g/ml;
P= 98%
Daniel, Alfano, Venditto, Cardea, Reverchon, Mensitieri, Guerra Adv. Mater. 2005, 17, 1515
Syndiotactic Polystyrene:
some applications
 molecular sensors
Quartz crystal microbalance (QCM)
Mensitieri, Venditto, Guerra Sensors and Actuators B, 2003, 92, 255
Fiber optic sensor
Giordano, Cusano, Mensitieri, Guerra Sensors and Actuators B, 2005, 109, 177
 air and water purification
Venditto, Del Mauro, Mensitieri, Milano, Musto, Rizzo, Guerra Chem. Mater. 2006, 18, 2205
gas storage
Annunziata, Albunia, Venditto, Mensitieri, Guerra Macromol. 2006, 39, 9166
Ethylene
The simplest unsaturated hydrocarbon regulates a multitude of plant processes,
from seed germination to organ senescence. Of particular economic importance is
its role as an inducer of fruit ripening.
CH3 – S – CH2 – CH2 –CH – COO–
NH3+
L-methionine
CH3 – S+ – CH2 – CH2 –CH – COO–
NH3+
adenine-ribose
NH3+
CH2
1-amminocyclopropane1-carboxylic acid (ACC)
C
COO –
CH2
ACC oxidase
½ O2
HCN + CO2
H2C
CH2
The enemies of fresh produce
Ethylene, CO2  Senescence
produce
Response to ethylene
Response to CO2
apple ‘Golden
Delicious’
Ripening /decay
>15%
off flavor (fermentation) browning, lesions
kiwi
>10 ppb
softening
>7%
breakdown of the flesh
broccoli
2 ppm
reduce shelf-life of 50%
>10%
sulfur containing volatiles
carrot
0.5 ppm
bitterness
>5%
spoilage
lettuce
Russet spotting
>2%
brown stain
Water loss  Shrivel
A water loss of 2% of product weight can
become noticeable.
Release of ethylene and CO2
produce
Ethylene production
(L/kg h)
Respiration rate
(CO2, mL /kg h)
apple ‘Golden
Delicious’
20 – 150
15 – 30
plum
0.1-200
8.2
kiwi
0.1 – 100
15 – 20
broccoli
< 0.1
140 – 160
carrot
> 0.1
50 – 120
lettuce
< 0.1
25 – 30
Postharvest Technology Research and Information Center
Department of Pomology University of California
One Shields Ave., Davis, CA 95616-8683
Ethylene and CO2 uptake in crystalline polymeric phase
CO2
ethylene
1,0

0,10
0,6
//

//
0,05
0,8
0,5
950
Absorbance
Absorbance
0,00
1000
0,4
0,3
0,6
0,4
0,2
0,2
0,1
0,0
1100
0,0
1050
1000
950
900
-1
Wavenumber (cm )
850
2300
2350
-1
Wavenumber (cm )
Dichroic guest peaks  guest included in the crystalline phase
Dichroism measurements allow to determine the orientation of the guest
molecule in the cavity.
With respect to the chain axis, the ethylene molecular plane forms an angle of 41° while the
CO2 long axis forms an angle of 69°.
Ethylene uptake and desorption
3,0
T=23°C
0,20
Absorbance
Film samples thickness: 80 m
0,15
2,0
1,5
0,10
1,0
0,05
d
0,5
PP/SiO2
0,00 
1,0
0
 s-PS
0,0
200
400
PP/SiO2
600
800
1000
time (minutes)
d s-PS
am s-PS
0,8
am
Amorphous phase: D  10-13 m2/sec
(At-A0)/A0
0,6
d
0,4
0,2
T=23°C
0,0
0
5000
10000
15000
t/L
20000
25000
30000
35000
D  10-14 m2/sec
Ethylene uptake (wt %)
2,5
Diffusivity control by crystalline phase orientation:
(002)
a
L
unor
010)
002)
(010)
½
0,1
0,8
0,1
O=
C
(210)
0,1
0,1
L
(At-A0)/A0
0,6
0,4
(210)
0,2
d s-PS
0,0
T=23°C
0
10000 20000 30000 40000 50000 60000 70000 80000
t/L
b
=O
½
_
1,0
R
½
R
Absorbance
Absorbance
Test with apples
apples
CO2
H2O
2338 2334
H2O
commercial
PP/SiO2
CO2
s-PS d form
3600
3400
3200 2400
-1
Wavenumber (cm )
2350
2300
Conclusions
d form s-PS samples show:
• CO2 and ethylene absorption in the crystalline phase
• high weight uptake
( 4 times larger than for commercial films containing 25% of high surface silica)
• orientation control of diffusivity
• no water uptake
This cheap, robust and easy-to-process polymeric
material is suitable for (also repeated use) food
packaging requiring ethylene and CO2 removal.
Freshness preserving agents
Ethylene absorbers:
KMnO4 coated zeolite pellets
Letto catalitico at T close
to 250° C.
CO2 absorbers:
“…facendo passare in circuito chiuso l'atmosfera
ricca di CO2 prelevata dalla cella attraverso un
particolare supporto di "carbone attivo".
Esso, grazie alla specifica dimensione dei suoi
"micropori" ed alla enorme superficie di reazione,
possiede la capacità di trattenere selettivamente le
molecole di CO2.”
www.4theegg.com www.isolcell.it
Freshness preserving agents
Active & intelligent packaging
Modified Atmosphere Packaging system (MAP).
Traditionally used packaging films like LDPE (low density polyethylene) and OPP
(oriented polypropylene) are impregnated with additives to become permeable
enough for highly respiring products like fresh-cut produces.
Common additives: natural clays, ceramics, zeolites, metal oxides, silica, carbon.*
www.peakfreshusa.com
* DiSTAM – Università degli studi di Milano
www.grofitpl.com
Activation energy of ethylene diffusion
Ethylene desorption from unoriented δ-form
s-PS films, at different temperatures in
the range -5,+70°C.
70
60
50 40
25
-28
12
1,0
4
2
-5
lnD (m /sec)
(At-A0)/A0
-26
0,5
d s-PS

-30
am
d-210
-32
0,0
0
20000
40000
60000
80000
t/L
dunor
-34
d010
Ea  kcal/mol 10
d002
-36
-3
2,8x10
-3
3,2x10
1/T (1/K)
-3
3,6x10