Radiation Physics and Chemistry 63 (2002) 493–496
Radiation crosslinking of polyamide 610
W. Fenga,*, F.M. Hub, L.H. Yuana, Y. Zhoua, Y.Y. Zhoua
aFaculty of Chemistry, Key Laboratory for Radiation Physics and Technology of Ministry of Education, Institute of Nuclear Science and
Technology, Sichuan University, Chengdu 610064, Sichuan, People’s Republic of ChinabChenguang Research Institute of Chemical Industry, Chengdu 610041, Sichuan, People’s Republic of China
Abstract
In the present paper the gel formation of polyamide 610 by g-ray irradiation in the presence of polyfunctionalmonomer and g-crystal nucleating agent under vacuum or air atmosphere had been studied. It was found that the gelformation was dependent on the content of polyfunctional monomer and nucleating agent. However, there was very
little difference between gel contents irradiated under vacuum and air atmosphere. The results showed that the
crosslinking by g-irradiation enhanced the mechanical properties of PA610 especially at high temperature in thepresence of polyfunctional monomer and g-crystal nucleating agent. The mechanism of radiation crosslinking andscission was discussed according to the composition and quantity of gas released from three kinds of PA during
irradiation. r 2002 Published by Elsevier Science Ltd.
Keywords: Polyamide 610; Irradiation; Crosslinking
1. Introduction
Polyamide resins are in the category of engineering
plastics since they have excellent physico-mechanical
properties. Further enhancing the physico-mechanical
properties especially the heat-resistance by means of
radiation crosslinking is still interesting to many
radiation chemists (Zhang et al., 1984; Li et al.,
1996a,b; Ueno, 1990). The crosslinking reaction of
polyamide is often simultaneous with the scission
reaction during irradiation. The relationship between
crosslinking and scission for polyamides is dependent
mainly on the length of methylene group chain in the
polyamide macromolecules and the condition of crystal-
linity (Deev et al., 1980). In this paper the radiation
crosslinking of polyamide 610 in the presence of
crosslinker, g-crystal nucleating agent and filler havebeen studied. The possible mechanism of crosslinking
and scission was discussed.
2. Experimental
2.1. Material
PA610 was purchased from Helongjiang Institute
of chemical Industry; triallyl isocyanate (TAIC) was
imported from Russia; potassium iodide (KI), iodine (I2)
and m-cresol were obtained from Shanghai Chemical
Reagent Station. Talcum powder was in commercial
grade. All materials were used without further handling.
2.2. Sample preparation
PA610 samples for radiation were prepared by
blending the different additives in a twin-screw extruder.
The samples for tensile strength test were prepared in the
injection machine (made in Germany ARURG). The
granular of PA were charged into the specially made
ampoules. After being subjected to evacuation of the
ampoules for 24 h, the samples were sealed in ampoules
followed by irradiating with 60Co g-ray at variousirradiation doses.
*Corresponding author. Tel.: +86-28-541-0252.
E-mail address: [email protected] (W. Feng).
0969-806X/02/$ - see front matter r 2002 Published by Elsevier Science Ltd.
PII: S 0 9 6 9 - 8 0 6 X ( 0 1 ) 0 0 6 3 5 - 1
2.3. The measurement of gel content
0.3 g of irradiated samples of PA610 at various dose
were accurately weighed and put into the Soxhlet
extractor. After extracting with m-cresol for 48 h and
with methanol for 24 h, the residue was dried in the
vacuum oven till the constant weight was obtained,
based on which the gel content was calculated.
2.4. The measurement of properties
The size of dumbbell sample was 60� 10� 3� 2mm.The tensile strength and elongation were determined by
using WD-5 Electron Universal Testing Equipment. The
tensile strength at 2201C was measured by the machine
equipped with a heat oven designed by us.
The total quantity and composition of gas released
from the PA samples during irradiation were measured
by gas chromatography (PERKAN-ELMER SIG-
MA15).
3. Results and discussion
3.1. The effects of additives and irradiation atmosphere
on PA610
The effects of various additives of TAIC, filler of
talcum powder and g-crystal nucleating agents of KI andI2 (Deev et al., 1980) on the formation of gel of PA610
during irradiation are shown in Figs. 1–4. It can be seen
from the Fig. 1 that there was almost no formation of
gel in the absence of TAIC, indicating that the cross-
linking and scission occurred simultaneously during
irradiation of PA610. While the addition of 5 phr TAIC
led to a marked increase of the gel content up to about
75%, which demonstrated that the crosslinking pre-
dominated over the scission reaction. On comparing
PA610-TAIC it can be clearly seen that the overall
tendency in density of the network is in the order of
PA610-5 phrTAIC>PA610–3 phrTAIC>PA610. Thus,
TAIC is very effective here as a crosslinking additive for
PA 610 under irradiation.
0 75 150 225 300 375 4500
20
40
60
80
Gel
Con
tent
/%
Dose/kGy
Fig. 1. The effect of polyfunctional monomer on gel formation
of PA610 during irradiation in air TAIC: (’) 5 phr; (�) 3 phr;(m) 0 phr.
0 75 150 225 300 375 4500
20
40
60
80
Gel
Con
tent
/%
Dose/kGy
Fig. 2. The effect of filler content on gel formation of PA610
during irradiation in vacuum (TAIC: 3 phr) talcum: (’) 25 phr;
(�) 8 phr; (m) 4 phr (.) 2 phr; (E) 0 phr.
0 75 150 225 300 375 4500
20
40
60
80
Gel
Con
tent
/%
Dose/kGy
Fig. 3. The effect of filler content on gel formation of PA610
during irradiation in air (TAIC: 3 phr) talcum: (’) 25 phr; (�)8 phr; (m) 4 phr; (.) 2 phr; (E) 0 phr.
0 75 150 225 300 375 4500
20
40
60
80
Gel
Con
tent
/%
Dose/kGy
Fig. 4. The effect of crystal nucleating agent on gel formation
of PA610 during irradiation in air (TAIC: 3 phr) KI+I2: (�)0.06wt%+0.06%; (’) 0wt%.
W. Feng et al. / Radiation Physics and Chemistry 63 (2002) 493–496494
It is noteworthy that in the presence of both talcum
and TAIC the gel content rose faster with the increasing
of content of talcum powder than that in the presence of
TAIC as shown in Figs. 2 and 3. This implies that the gel
formation can also be accelerated both in vacuum and
air with talcum as an additive. In this case the residual
filler of talcum was not found from the crosslinked
PA610 upon extraction. It may suggest that during
irradiation of PA610 the link was formed between
talcum and macromolecule of PA610. Besides, there is
very little difference in the formation of gel for PA610 in
the atmosphere of air and vacuum. The minor influence
of air atmosphere on the process of gel formation may
be accounted for by the fact that PA610 was in granular
state and the diffusion of oxygen to the inside of
granular was very difficult. In the meanwhile KI+I2 was
found to be of benefit to gel formation during
irradiation of PA610 as shown in Fig. 4.The result is
similar to that reported by Deev (Deev et al., 1980)
3.2. The mechanical properties of radiation crosslinked
PA610
In Figs. 5 and 6 are given the influence of both
polyfunctional monomer and fillers on the mechanical
properties of PA610 during irradiation in air. For
PA610 with TAIC and filler the tensile strength grew
and the elongation at break decreased with increasing
the irradiation dose. In contrast, the tensile strength and
the elongation of PA610 without TAIC and talcum fell,
reflecting the degradation of PA610 during irradiation.
These results indicated that the presence of talcum
contributed to the formation of gel and density of
network of PA610-TAIC. The tensile strength of
irradiated PA610 at 2201C is shown in Fig. 7. Obviously,
the irradiated PA610 still had certain tensile strength at
this high temperature. The tensile strength increased
with the increasing of gel content and then tended to be
stationary. The tensile strength for irradiated PA610-
3 phrTAIC-8 phr talcum at 2201C was raised to 8MPa.
In contrast, the unirradiated PA610 already melted at
this temperature. Thus the PA 610 prepared here under
g-irradiation in the presence of TAIC or talcum viacrosslinking possessed the advantage in heat-resistance
over the unirradiated one at higher temperature.
3.3. Gases released from pure PA610 during irradiation
According to the structure of aliphatic polyamide the
macromolecule consisted of different length of methy-
lene group incorporated with amide group. However,
the similar backbone as polyethylene did not provide the
similar radiation-initiated reaction as observed here in
the scission reaction due to the weaker cyanic link in the
amide group. It means that the crosslinking and scission
were concomitant during irradiation of PA610. Mean-
while, gases were released accompanying the process of
crosslinking and scission of PA610 (Deev et al., 1980).
0 75 150 225 300 375 450
90
100
110
120
130
Ten
sile
Str
engt
h/M
Pa
Dose/kGy
Fig. 5. The effect of filler content on the tensile strength of
PA610 during irradiation in air talcum+TAIC: (’) 0 phr X
talcum+3phr TAIC: X: (E) 8 phr; (.) 4 phr; (m) 2 phr; (�)0 phr.
0 75 150 225 300 375 4500
50
100
150
200
250
Elo
ngat
ion/
%
Dose/kGy
Fig. 6. The effect of filler content on the elongation of PA610
during irradiation in air talcum+TAIC: (’) 0 phr X
talcum+3phrTAIC: X: (E) 8 phr; (.) 4 phr; (m) 2 phr; (�)0 phr.
0 10 20 30 40 50 600
2
4
6
8
10
Ten
sile
Str
engt
h/M
Pa
Dose/kGy
Fig. 7. The effect of filler content on tensile strength at 2201C
of PA610 (3 phr TAIC) at different dose in air X talcum (’)
8 phr; (�) 4 phr; (m) 2 phr; (.) 0 phr.
W. Feng et al. / Radiation Physics and Chemistry 63 (2002) 493–496 495
Gas chromatographic analysis demonstrated that the
gases were mainly composed of H2, CO and trace of
acetaldehyde. The yield of gases or G value of these
gases was dependent on the polyamide or the length of
the chain of methylene group in the polyamide macro-
molecule. The results of analysis are summarized in
Table 1. Obviously, hydrogen gas accounted for the
majority among the three components released and its
amount increased with increment of length of the chain
of methylene group.
Based on the above results, a similar mechanism
(Deev et al., 1980) of radiation crosslinking and scission
of PA610 during irradiation was proposed as follows:
2CH2CONH2CH2CH22
2r2CH22CONH2C
dH2CH22þH
d
2CH2CONH2CH2CH22þHd
-2CH22CONH2CdH2CH22þH2
22CH2CONH2CdH2CH22
-2CH22CONH2CH2CH22CH2
2CONH2CH2CH22
2CH22CONH2CH2CH22
2r2CH22C
dOþN
dH2CH22CH22
2CH22CH22CdO-2CH22C
dH2 þ CO
22CH22CdH2 þH2-22CH22CH3
2CH22CdOþN
dH2CH22CH22H2
-2CH22CHOþNH2CH22CH22
2CH22CH22CH22CHO
2r2CH22C
dH2 þ C
dH22CHO
2CdH22CHOþH2-2CH32CHO:
4. Conclusion
1. The crosslinking and scission occurred simulta-
neously during irradiation of PA 610. The presence
of TAIC, filler of talcum powder and g-crystalnucleating agents of KI and I2 was beneficial to
radiation crosslinking of PA 610
2. PA 610 in the presence of TAIC or talcum by g-irradiation crosslinking possessed the advantage in
heat-resistance over the unirradiated one, especially
at higher temperature (2201C), the tensile strength
was almost retained for irradiated PA 610.
3. The mechanism of crosslinking and scission during
irradiation of PA 610 was discussed based on the gas
released.
References
Deev, U.S., Subbotin, U.S., Riabov, E.A., 1980. Radiation-
chemical modification of polyamide. Plastmasse 4, 52.
Li, B.Z., Zhang, L.H., Yu, J.Y., 19963a. g-radiation damage tocrystalline polyamide 1010 containing heterogeneous. J.
Radiat. Res. Radiat. Proc. 14, 4.
Li, B.Z., Zhang, L.H., Yu, J.Y., 1996b. Post radiation effects on
polyamide 1010. J. Radiat. Res. Radiat. Proc. 14, 153.
Ueno, K., 1990. Section 2.3. CrosslinkingFthe radiationcrosslinking process and new products. Radiat. Phys. Chem.
35, 126.
Zhang, L.H., Li, S.Z., He, Z.D., Su, W., Zhang, Z.C., 1984.
Radiation-induced crosslinking of polyamide 1010. J.
Radiat. Res. Radiat. Proc. 3, 32.
Table 1
Released gases from polyamides during irradiation
Gas Radiation chemical yield (molecule/100 eV)
PA6 PA610 PA1010
H2 0.098 0.115 0.123
CO 0.0013 0.035 0.011
CH3CHO Trace Trace Trace
Total 0.0994 0.151 0.134
W. Feng et al. / Radiation Physics and Chemistry 63 (2002) 493–496496
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