annual report annual report annual report annual report 2005

32
RADIATION CHEMISTRY AND PHYSICS, RADIATION TECHNOLOGIES
[5]. Qin X.-Z., Trifunac A.D.: J. Phys. Chem., 94, 4751
(1990).
[6]. Danilczuk M., Sadlo J., Lund A., Hamada H., Michalik
J.: Nukleonika, 50, Suppl.2, S51 (2005).
[7]. Shiotani M., Yuasa F., Sohma J.: J. Phys. Chem., 75,
2669 (1975).
[8]. Danilczuk M., Pogocki D., Lund A., Michalik J.:
PCCP, 6, 1165 (2004).
[9]. O’Malley P.J., Collins S.J.: Chem. Phys. Lett., 259,
296 (1996).
[10]. O’Malley P.J.: Chem. Phys. Lett., 262, 797 (1996).
[11]. O’Malley P.J.: J. Phys. Chem. A, 101, 6334 (1997).
[12]. O’Malley P.J.: J. Phys Chem. A, 101, 9813 (1997).
[13]. O’Malley P.J.: J. Phys Chem. A, 102, 248 (1998).
[14]. Barone V.: Structure, magnetic properties and reactivities
of open-shell species from density functional
and self-consistent hybrid methods. In: Recent advances
in density functional methods. Part I. Ed. D.P.
Chong. World Scientific Publ. Co., Singapore 1996.
[15]. Becke A.D.: J. Chem. Phys., 98, 5648 (1993).
[16]. Frisch M.J. et al.: Gaussian 98. (Rev.A.7). Gaussian
Inc., Pittsburgh 1998.
[17]. Yanagita Y., Amaro A.A., Seff K.: J. Phys. Chem.,
77, 805 (1973).
[18]. Pluth J.J., Smith J.V.: J. Am. Chem. Soc., 102, 4704
(1980).
[19]. Ya-Jun Liu, Lund A., Persson P., Lunell S.: J. Phys.
Chem. B, 109, 7948 (2005).
EFFECT OF HINDERED AMINE LIGHT STABILIZERS
ON RADIATION RESISTANCE OF POLYPROPYLENE
MEASURED BY DSC
Andrzej Rafalski, Grażyna Przybytniak
In many polymers, hindered amine light stabilizers
(HALSs) are used as radical scavengers and antioxidants
to protect material against photodegradation
[1]. It is generally accepted that the decomposition
of polyolefines initiated by ionizing radiation
proceeds comparably to UV-induced degradation,
i.e. via free radical mechanism [2,3], thus
the application of amine stabilizer as a protecting
agent against radio-degradation is fully entitled.
Oxidative damage is the main reason for applying
antioxidants as the radioprotective agents in polypropylene
(PP). HALSs are well known radical
scavengers that inhibit the propagation of free radicals
acting as their scavengers.
Two various phases occur in isotactic polypropylene
(iPP) – ordered domains of the crystalline
phase and variety of amorphous sites [2]. Thus,
there are two types of peroxyl radicals formed during
irradiaton and situated in the totally different
vicinity. Random orientation of macromolecules
in the amorphous phase facilitates peroxyl radical
mobility and involves their faster decay. Therefore,
the amount of the radicals considerably decreases
in presence of stabilizers. Defined rigid structure
of crystal delays the combination of radicals and
the unpaired electron is transferred into other sites
inducing postirradiation damages for months. Assuming
homogeneous distribution of modifiers added
to polypropylene in melted state, we found unambiguously
that radicals are scavenged by HALSs
predominantly in amorphous phase as in presence
of hindered amines a significant decrease in characteristic
electron paramagnetic resonance (EPR)
signal of peroxyl radical just in this phase was observed
[4].
Differential scanning calorimetry (DSC) method
was applied to characterize physical properties of
isotactic polypropylene modified by selected
HALSs before and after irradiation. Three types
of amine stabilizers were applied: two derivatives
of 1,2,2,6,6-pentamethyl piperidine of low and high
molecular weight (Tinuvin 765 and Tinuvin 622,
respectively) and one polymeric derivative of
2,2,6,6-tetramethyl piperidine (Chimassorb 944).
In order to increase the compatibility of HALS –
polymer macromolecules, maleic anhydride (MA)
was added to the composites. Physical alternations
were estimated comparing changes in phase transitions
and crystallization temperatures before and
after electron beam exposure.
Isotactic polypropylene (Malen P J601) was
mixed with the following additives: Tinuvin 622
(T622), Tinuvin 675 (T675) and Chimassorb 944
(C944). Selected samples were mixed with maleic
anhydride. Samples were prepared in a Brabender
mixer at 180 o C and subsequently compressed between
two metal plates quenching with water. Concentration
of additives is expressed as the parts per
hundred resin (phr). Irradiation with a 10 MeV electron
beam was performed using a linear accelerator
LAE 13/9 in air at ambient temperature. All
samples were irradiated to a dose of 25 kGy.
Thermal analysis was carried out using a TA
Instruments differential scanning calorimeter
(MDSC 2920). The measurements were performed
under nitrogen at a heating rate of 10 o C/min. About
5 mg samples were placed in aluminum pans and
inserted in the cell. During the first cycle, the cell
was heated from the ambient temperature to
200 o C, then kept for 5 min at this temperature and
gradually cooled. The second run was performed
afterwards applying the same conditions as for the
first cycle.
Phase transitions of polypropylene are influenced
by electron beam irradiation. The melting
behavior of polypropylene shown in Fig.1A indicates
that the melting peak obtained during the
first cycle at 163 o C, in the second cycle becomes
wider due to increase of low temperature endotherm.
For irradiated polypropylene, a single peak
detected during first heating splits in the second
cycle and two distinct minima are observed. High
temperature melting peak is less intensive, whereas
the intensity of low temperature peak significantly
increases indicating that ionizing radiation induces
changes in morphology of the polymeric material.
Multiple-peak endotherms reveal separation of
different crystals that occurs during slow recrys-