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