Vol. 19 No. 2 Journal of Wuhan University of Technology - Mater. SCi. Ed. June 2004

Graft Polymerizat ion of Acrylic Acid and Acrylamide onto

BOPET Corona Films *

SUN Jie ') TIAN Hua-yu 2) BAI Yong-ping ~ W u h a n Inst i tute o f Science and Technology 2)Harbin Institute of Technology

( Received: March 15,2003; Accerted: April 15,2004) Abslratl: The grq/'t pol)merization of acrylic acid( A ) and cu:rylamide ( B ) was carried out onto bi-ori-

ented polyester BOPET corona film. The. influence of monomer concentration, reducer concentration mul reaction time on the graft polymerization was investignted. The surface tera~ion of the films increased with cm increca~e of monomer concentration, till the concvntration of monomer A reached 1.5 • 10- ~" g~ mL and the conceatration of monomer B reached 4.0 x 10-2 g~ mL. The surface terasion of the f t l ~ reached a max/mum t~ue at 7 • 10-4 M of reducer concentration and subseqacntly decreased with further increca~e in reducer concentration. The slwface ten-

sion of the f i l ~ increased whh the increcL~e of the re~tion time apparently within 50rain. The grafted corona 130- PET films were characterized with IR and XPS. The presence of graft on the film surface ~ confirmed. The atten- uation expedmenLs on grqlted corono BOPET films in air at 50~C and in water uere corned out to/m~eztigate the persistence of graft polymerization of acrylic acid and arylamide onto BOPET corona films.

Key words: BOPET ; corona film ; graft polymeriaaion

1 Introduction

BOPET films are more and more widely used in agri- culture., packing, electricity and so on for their excellent

property ttl . But the further applications of BOPET films are limited in printing plating, adhesion etc due to their lower surface polarity, hydrophohie property and poor wet- ting property. As a result, the surface modification of BO- PI'~ films to improve their surface tension is necessary. The methods of oxidation and chemically picking can be used, but the bulk property of BOPET films would be af- fected. The surface polarity of BOPET films can be en- hanced by corona modification, but can not maintain for a

long time ̀ >< . In this paper the graft polymerization of acrylic acid and acrylarmide was carried out onto BOPET films and mtMification effects were characterized by XPS and IR methods.

2 Experimental

2.1 Principle Although there are not many active groups on the

surface of BOPET films for chemical reaction, the surface of BOPET films will generate peroxide groups after corona treatment. In addition, the carbonyl group, aldehyde group, ketone group etc will appear on the surface of BO- PET films because of the chain-scission degradation of some of the polyester molecular. Peroxide groups react with reducer to generate active groups which can initiate

SUN J i e ( ' t ' ~ ) : Born in 1976; Iee/ure; Master; Environment and Chemistry Department, Wuhan Institute of Science and Technol- ogy, Wuhan 430073, China

* Funded by the National Natural Science Foundation of Chi- na(No.50309011 )

grafting reaction. The common ways of grafting are gas- phase grafting, liquid-phase grafting and solid-phase graft- ing. In this paper, liquid-phase grafting with reducer was carried out on the corona films because it can be, easily controlled. The principle of the grafting polymerization is as following:

Corona reAneer Ireatment ~ r

PET molecules OOR

m o n o m e r

o" o-pa).

Fig. 1 "llae principle of grafting modification of BOPET corona films

Mohr' s .'salt was the reducer in the experiment for its water solubility and high activity. The solution of acrylic acid and acrylamide was used for graft polymerization. 2.2 Materials

BOPET corona films: offered by Xinlike Plastic Ce- ment Company in Shandong province, 0. 025nrm in thick- ness; Acrylic acid: chemically pure ( A ) ; Acrylamide: chemically pure.(B) ; Mohr' s salt: chemically pure. 2 .3 Procedure

The graft polymerization of acrylic acid and acrylam- ide with a certain ratio onto BOPET corona films was car- ried out in a reaction vessel. A film was placed in the re- action vessel containing an aqueous solution of the reduc- er, acrylic acid and acrylamide. After the grafting reaction for a specified period, the film was removed from the re.ac- tion vessel and put into thin chlorohydric acid. Then the film was extracted with methyl alcohol and washed with distilled water followed by drying at room temperature.

Vol. 19 No. 2 SUN Jie et d:Graft Polymerization of Acrylic Acid and Acrylamide... 91

64 63

~" 62

~61 o �9 ~ 60 -~ 59

~ 58

57

56 0

i i | i |

0.5 1 1.5 2 2.5 T h e c o n c e n t r a t i o n o f m o n o m e r AI(10-:g/mL)

Fig.2 "lhe infl~nce on the, surface tension of the grafted corona film of the concentration of monomer A

6,1

62

5s

57

// 513 , , ,

0 2 4 6 The concentration of monomer B/(IO 2g/mL)

lqg.3 "lhe irduea~ on ~ surface tens~ of the grafted corona film of the concentration of monomer B

70

65

',~ 55

45

40 0 15

Fig.4

i |

5 10 The concentration of redueer/10"M

"Ihe influence, on the surface, tension of grafted corona film of leducer concentration

Corona film and grafted corona film were heated re- spectively in hot air at 50~C for a specified period for hot air attenuation. Corona film and grafted corona film were immerged in water for a specified period for water attenu- ation. 2 .4 Measurement and instrmnents

The surface of BOPET film was applied with the so- lutions made of methane mnide and ethandio with different surface tension respectively. If the solution on the surface of BOPET films neither contracted nor showed blank space, the surface tension of BOPET films was the same with that of the solution.

A Nicole 750 total reflection IR spectrometer was u.~xt for IR spectra measurement. A PHI 5300 ESCA was used for XPS measurement.

3 Results and Discussion

3.1 Factors affecting the graf t polymerizat ion 3 . 1 . 1 Influence of monomer concentration

The differences of the surface tension of the films re- fleet the diverse effect of graft polymerization. The influ- ence of the concentration of monomer A on the graft poly- merization is pre~nted in Fig. 2. When monomer A is at low concentration, the surface tension of film increases with an increa~ of the concentration of monomer A be- cause the effect of graft gets better with the contract of monomer A with the free radical on the surface of BOPET films. When the concentration of monomer A is over 1 .5

• 10-2g/mL, the surface tension of the film does not in- crease apparently, because the increase of the homopoly- rner based on monomer A prevents from the diffusion of monomer A to the surface of the films. As shown in Fig. 3, the influence of the concentration of monomer B on the effect of graft is similar to that of monomer B. When

the concentration of monomer B is over 4 x 10-2 g/mL, the surface tension of the film does not increase with an in- crease of the concentration of monomer B apparently. Therefore, the optimum conditions of monomer A and B

are 1.5 x 10-2g/mL and 4 x 10-:g/mL,respectively. 3 . 1 . 2 Influence of reducer concentration

The influence of the reducer concentration on the

graft polymerization at room temperature is shown in Fig.4. The surface tension of the wafted corona film in- creases with an increase of the reducer concentration. The surface tension of the fihns reaches a maximum value at

reducer concentration of 7 x 10-4M and thendecreases with further increase in reducer concentration, becau~ ex- cess reducer can catch the free radical and hence prevent from the graft polymerization. Therefore, the optimum con-

dition of the reducer concentration is 7 x 10-4M. 3 . 1 . 3 Influence of reaction time

The influence of reaction time! on ihe surf~e ten- sion of the grafted corona film is shown in Fig. 5. The sur- face tension of the grafted corona film increases with an increase of reaction time sharply. When reaction time is over 50min, the graft ratio does not increase with an in- crease of reaction time apparently, because more monomers diffu~ to the surface of BOPET films. Therefore, the graft polymerization becomes much easier. However, the surface tension of the filrns will decrea~ when the reaction time is over 50min. It may be possible that the diffusion of the monomers to the surface of the films is prohibited because of the decrease of monomer concentration and the forma- tion of homopolymer.

65

" 6O

55

50

~ 45

417 0

i

2o Reaction time/min

80

Fig. 5 The influence on the surface tension of grafted corona film of reaction time

3 . 1 . 4 Determination of the conditions of graft polymer- ization

The comprehensive experiments were made on the basis of the rules of the above factogrs affecting the effect of graft. The optimum conditions of graft polymerization are determined as the following: the concentration of

92 Journal of Wuhan University of Technology - Mater. Sci. Ed. June 2004

monomer C is 1 . 5 x 10 -2 g/mE, the concentration of

monomer D is 4 x 10-2g/mL, the reducer concentration is

7 x 10 -4 M and the reaction time is 50rain at room tem- perature. Under the optimum conditions, the surface ten- sion of the grafted corona film can reach 70mN/m. 3 .2 Characterization of grafted corona film 3 .2 .1 Characterization with IR spectra

The IR spectra of non-corona film, corona film and grafted corona film are shownin Fig. 6. The new peaks of

carbonyl appear ( 1650.4cm -1 , 1630.8cm -1 ) and the

peaks o f - - C - - @ - - at 1260 cm -t and l l l0cm -1 split in- to multiply peaks, indicating that the molecules on the surface are oxygenated to carbonyl and - - C - - O - - , which is due to the chain-scission degradation of polyester and the forms of ketonic type and aldehydic type during the cause of corona. Mter corona films have been grafted, the spitted peaks near the peaks of carbonyl are more appar-

ent. The new peaks of carbonyl appear (1710cm -t , 1678.1 cm -t , 1648. 8cm -t ) , the peak of - - C - - O - - splits into multiple peaks. The peaks of bend vibration and expansion vibration of the bond of - - N - - H - - appear at

1600cm- 1 and 1026.3cm- a. It indicates that carbonyl , - C - O - - - and - - N - - H - - , which are different from the en- tity structure of polyester, form on the surface of grafted BOPET films.

90 80 70 6O 50

"~ 40 30

�9 ~ 20 1o 0

-10 -20 -30

lsoo 170o teoo t~o t4oo t3o0 l ~ t~o0 1~0 9~o s~o 700 Wavenum]~rs/em -~

Fig. 6 The total reflection IR spectra of three kinds of

BOPET fihns(part)

3 . 2 . 2 Characterization with XPS Table 1 "Ilae content of the elements on the surface of three Idnds

of BOPET films( the g~lancing angle of XPS is 45 ~

C/% 0/% N/% (0/C)/% (N/C) %

non-corona film 72.45 27.55 0.00 38.00 0.00

corona film 68.90 31.10 0.70 45.10 1.02

~dco~afilm 70.42 28.06 1.52 39.8 2.16

Table 1 shows the content of oxygen atoms, nitrogen atoms and carbon atoms on the surface of BOPET film and the values of O/C and N/C by XPS.

After corona treatment, the content of oxygen atoms on the surface of the BOPET corona film increases appar- ently and a small mumber of nitrogen atoms appears, be- cause during corona treatment the molecular on the surface reacts with the component ionized in air to introduce po- larity groups with nitrogen atoms and oxygen atoms of the action of the energetic particle. After graft polymerization, the content of nitrogen atoms on the surface increases,

which can be attributed to nitrogen atoms in the monomer participating in graft. The content of oxygen atoms on the surface decreases, because the peroxidate groups on the surface of the corona film participate in the free radical initiating action and a part of oxygen atoms disappears. In addition, the polarity groups with oxygen atoms migrate to- wards the inner surface, and some polarity groups with low molecular diffuse into water. Oxygen atoms in the arylic acid monomer introduced in graft polymerization are less than those lost. 3.3 Attenuation experiments 3.3 .1 Attenuation experiment in the hot air

Fig. 7 shows the relationship between the surface tension and the heating time of corona films and grafted corona films in air at 50 ~C. As shown in Fig. 7 ( a ) , the surface tension of the corona film attenuates with an in- crease of heating time. As shown in Fig. 7 ( b ) , the surface tension of the grafted corona films does not change with heating time apparently.

Oq

55 53

5t

49

47

45

43

41

39

37 35

0

,•*** (a) corona film

100 200 300 Attenuation time/min

400

75

70,, ,r : *

65 (b) grafted corona film

~ 55

~ 50

45

4O

35 l I / l

0 2 4 6 8 10 Attenuation time/d

Fig, 7 The attenuation experiment in hot air on the corona

film and grafted corona film

It is possible that the polarity groups on the surface migrate towards the inner surface after the corona films are heated, proved by the data in Table 2.

Table 2 ESCA measurement result of attenuated corona film in the hot air

(o/c)/% 20 ~ 45 ~ 70 ~

non-attenuated film 46.60 45.10 - -

attenuation for 30min 43.50 44,80 - -

attenuation for 2h 43.00 43.90 45.20

Table 2 shows the results of XPS with angle changing of the attenuation experiments of the corona film in air at 50~C. It is sho~aa that the content of oxygen atoms in the different depth of the corona film surface before attenu-

Vol. 19 No. 2 SUN Jie et d : G r a f t Polymerization of Acrylic Acid and Acrylamide. . . 93

ation differs from that after attenuation greatly. The content of oxygen atoms increases with an increase of depth on the corona film surface after attenuation. But the content of oxygen atoms decreases with an increase of depth under the surface of the corona film before, attenuation. This in- dicates that the motion ability of the polarity groups in- creases in hot air,and the groups with oxygen migrate from the outer surface into the inner surface to reach the bal- ance gradu',dly.

The monomers used for graft containing long chain ~ th polarity groups distribute on the surface of grafted co- rona film with a certain thickness, which leads to the large intermolecular force among them. As a result, the migra- tion of the polarity groups from outer surface to irmer sur- face is diffieuh. Therefore, the polarity groups rcmain on the outer surface of the films persistencely. 3 . 3 . 2 Attenuation experiment in water

Fig. 8 shows the relationship between the surface tension and the time of imn~rging in water of corona film and grafted corona film. The change of the surface tension with the attenuation time in water is similar to that in hot air. The surface tension of the corona films attenuates more quickly in water than in hot air. The surface tension of the corona film in water goes down from 54mN/m to 42mN/m 'after 30s. By contrast, the surface tension of the grafted corona films only changes a little from 70mN/m to 68mN/m after 10 days.

55 53'

z 49

~ 47 ~ 45 ~ 43

~ 39

37 3: ,

0 2

(a)corona film

Attenuation Time/d

70

5 5 ~ (h)grafted corona film s ~ 50

45

I ! t I i

0 2 4 6 8 10 Attenuation Time/d

Fig. 8 "]'he attenuation experiment in water of corona film and grafted corona film

It is possible that with the action of water some po- larity groups with low molecular weight fonned in the course of corona are removed from the surface of the coro- na film into water. In addition, water accelerates the mi-

gration of polarity groups from the outer surface to the in- ner surface. The results of XPS with angle changing of at- tenuation experiment of corona film in water are shown in Table 3. It indicates that the content of oxygen atoms in the outer surface of the corona film decreases rapidly.

Table 3 The results of ESCA element analysis with angle changing of the attenuation experiment of corona film in the water

(O/C)/%

20 ~ 45 ~ 70 ~

Non-irm~rging in the water 46.6 45.1 -

lmmerging in the water for 30s 43.0 46.6 -

Immerging in the water for 120s 37.7 40.2 40.9

Water h',mtly influences the grafted corona film in the attenuation in water. The monomers used for graft con- tain long chains with polarity, which results in the large intermolecular force. As a result, polarity groups are diffi- cult to be removed by water and migrate from the outer surface to the inner surface of the film. Therefore, the sur- face tension of the grafted corona film in the attenuation experiment in water does not change much.

4 Conclusions

The graft polymerization of acrylic acid and acrylam- ide was carried out onto BOPET corona films. The influ- ence of monomer concentration, reducer concentration and reaction time on o'aft polymerization was investigated. The optimum parameters for graft polymerization at room tem- perature are as follows:the concentration of monomer C is

1 . 5 • 10-2g/mI., the concentration of monomer D 4 •

10-2g/mL, the reducer concentration 7 • 10-4M and the reaction time 50min. Under the optimum parameters, the surface tension of grafted corona BOPET film can reach 70mN/m. The surface tension of the grafted corona films, which are put in air for 10h at 50"C and in water for more. than 10d, does not attenuate apparently.

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