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
It is able to absorb rapidly and selectively molecules already at low concentration.
Syndiotactic Polystyrene: termoplastic molecular sieve
– CH – CH2 – CH – CH2–
Tm= 270°C
Fast crystallization (Xc=30 – 60%)
Complex polymorphic behavior
(5 crystalline forms)
The nanoporous s-PS form presents a permanent cavity of 120-160 Å3 per 4 monomer units.
S-PS fibrils presenting the nanoporous phase
diameters of the fibrils 40-70 nm
sPS/toluene 2/98 g/g
=0.865 g/ml
sPS
=0.023 g/ml; P= 98%
Solvent removal from s-PS gel by supercritical CO2
Aerogel
Gel
Syndiotactic Polystyrene: aerogels
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
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+
CH3 – S+ – CH2 – CH2 –CH – COO–
adenine-ribose NH3+
CH2 NH3+
C
CH2 COO – ½ O2 ACC oxidase HCN + CO2 H2C CH2
1-amminocyclopropane-1-carboxylic acid (ACC)
L-methionine
Ethylene
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
The enemies of fresh produce
Ethylene, CO2 Senescence
Water loss Shrivel A water loss of 2% of product weight can become noticeable.
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 CenterDepartment of Pomology University of California One Shields Ave., Davis, CA 95616-8683
Release of ethylene and CO2
Ethylene and CO2 uptake in crystalline polymeric phase
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 CO2
95010000,00
0,05
0,10
8509009501000105011000,0
0,1
0,2
0,3
0,4
0,5
0,6 //
Abs
orba
nce
Wavenumber (cm-1)
2350 23000,0
0,2
0,4
0,6
0,8
1,0
Ab
sorb
an
ce
Wavenumber (cm-1)
//
Film samples thickness: 80 m
Ethylene uptake and desorption
Amorphous phase: D 10-13 m2/sec
D 10-14 m2/sec
0,0
0,5
1,0
1,5
2,0
2,5
3,0
0 200 400 600 800 1000
0,00
0,05
0,10
0,15
0,20
PP/SiO2
T=23°C
Ab
sorb
an
cetime (minutes)
am
Eth
yle
ne
up
take
(w
t %
)
0 5000 10000 15000 20000 25000 30000 35000
0,0
0,2
0,4
0,6
0,8
1,0
am s-PS
s-PS
T=23°C
t/L
(At-A
0)/A
0
s-PS
PP/SiO2
Diffusivity control by crystalline phase orientation:
a
b
L
RL
R
(002 )
(010 )
(210 )-
½
½
½
O=C=O
0,1 0,1
0,1 0,1
0 10000 20000 30000 40000 50000 60000 70000 80000
0,0
0,2
0,4
0,6
0,8
1,0
s-PST=23°C
010)
t/L
(At-A
0)/A
0
002)(210)
unor
_
Test with apples
3600 3400 3200 2400 2350 2300
Ab
sorb
an
ce
Wavenumber (cm-1)
CO2
H2O 23342338
commercial PP/SiO
2
s-PS form
Ab
sorb
an
ceCO
2H2Oapples
Conclusions
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
KMnO4 coated zeolite pellets
Ethylene absorbers:
Letto catalitico at T close to 250° C.
“…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.”
CO2 absorbers:
www.4theegg.com www.isolcell.it
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.*
Freshness preserving agents
Active & intelligent packaging
Modified Atmosphere Packaging system (MAP).
www.grofitpl.com www.peakfreshusa.com
* DiSTAM – Università degli studi di Milano
2,8x10-3 3,2x10-3 3,6x10-3
-36
-34
-32
-30
-28
-26
010
-210
unor
lnD
(m
2/s
ec)
1/T (1/K)
002
am
Activation energy of ethylene diffusion
Ethylene desorption from unoriented δ-form s-PS films, at different temperatures in the range -5,+70°C.
0 20000 40000 60000 80000
0,0
0,5
1,0
s-PS
t/L
(At-A
0)/A
0
-5
4
122570 60 50 40
Ea kcal/mol 10