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: wfeng95@163.net (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