- Email: [email protected]
Bionolle blend
Polymer Degradation and Stability 63 (1999) 311±320
Radiation eect on the mechanical stability and biodegradability of CPP/Bionolle blend Zainuddin a,*, Mirzan Thabrani Razzak a, Fumio Yoshii b, Keizo Makuuchi b a
National Atomic Energy Agency, Center for the Applications of Isotopes and Radiation, Jl. Cinere Pasar Jumat, PO Box 7002 JKSKL, Jakarta 12070, Indonesia b Japan Atomic Energy Research Institute, Takasaki Radiation Chemistry Research Establishment, 1233 Watanuki-machi, Takasaki-shi, Gunma-ken, 370-12 Japan Received 2 March 1998; received in revised form 15 June 1998; accepted 15 July 1998
Abstract Blends of polypropylene-co-ethylene (CPP) and polybutylene succinate (Bionolle) with polypropylene grafted maleic anhydride (Modic) as a compatibilizer were prepared by melt blending. Irradiation of the resultant polyblend was carried out using an electron beam in air. It was noted that the Modic compatibilizer also appears to act as a protective agent toward radiation degradation. The occurrence of crosslinking in the polyblend was observed, mainly contributed by Bionolle. However the whole process over all blend composition ranges was dominated by degradation. During indoor storage, the mechanical stability of irradiated polyblends was found to be fairly good, particularly compatibilized Bionolle and CPP/Bionolle (27/75). On the other hand, the sample buried in soil showed a drastic reduction in the over all mechanical properties. The extent of biodegradability as estimated from the weight loss increased with increasing Bionolle content. A synergistic eect on the weight loss was shown by compatibilized Bionolle and CPP/Bionolle (25/75). Additionally, even if the sample was no longer strong due to postirradiation degradation, the biodegradability of the polyblend was not much improved. Using a curve ®t model the time for complete weight loss was found to be approximately 14, 8, 7, and 12 months for unirradiated and irradiated Bionolle, compatibilized Bionolle, CPP/Bionolle (25/75) and (50/50), respectively. # 1999 Elsevier Science Ltd. All rights reserved.
1. Introduction To preserve the environment from harmful impact of solid waste plastic, synthesizing biodegradable plastics is highly in demand. For this purpose various approaches have been considered and were reported in our previous paper [1]. Melt-blending non-biodegradable and biodegradable polymer seems to be the best choice to manufacture biodegradable polyblends in the future. In the ®rst paper [1], we have reported the blending conditions and the optimum concentration of compatibilizer to obtain true molecular compatibility in the CPP/Bionolle blend over a wide composition range. In a second paper [2], we have discussed the biodegradability of Bionolle and its blend in two biotic environments, lipase-enzyme solution and soil burial. Nowadays, utilization of high energy radiation (gamma or electron beam) is commonplace in the mod* Corresponding author.
i®cation of polymers. As a result, numerous extensive studies on the irradiation of single polymers have been reported elsewhere. However, few studies have been made on the eect of irradiation on polyblends [3±6]. Irradiation of polyblends is generally aimed at introducing a desired amount of crosslinking or chain scission. Crosslinking will bring about an increase in tensile strength, elongation, modulus of elasticity, hardness, and softening temperature. On the other hand, chain scission decreases these properties [7±9]. The eects of gamma irradiation on mechanical properties and structure (crystallinity and density) of LDPE-iPP blend have been studied by Rizzo and his coworkers [10,11], and Kostoski [12]. The changes in physico-mechanical properties and thermostability of gamma irradiated PEPP blends have been elucidated by Gorelik [13]. The protective eects of vinyl groups in gamma irradiated PMMA±SAN and PMMA±PS blends have been reported by Nguyen [14]. The other eect, e.g. surface morphology and failure behavior of an irradiated polyblend were studied by Thomas [15], using PP±EVA blends.
0141-3910/99/$Ðsee front matter # 1999 Elsevier Science Ltd. All rights reserved PII: S0141 -3 910(98)00111 -6
312
Zainuddin et al./Polymer Degradation and Stability 63 (1999) 311±320
Nishi [16] studied the eect of electron beam irradiation on the cloud point behavior of PS±PVME system. In the current paper, we present our study in the radiation eect on the mechanical properties and biodegradability of compatibilized CPP/Bionolle blend.
2.2. Irradiation of the sample
2. Experimental
2.3. Sol-gel analysis
2.1. Materials
To remove the uncrosslinked or soluble part (sol fraction), the irradiated sample was extracted by using a suitable solvent. To dissolve CPP in the blends, decalin was used and chloroform for Bionolle. The extraction was done for approximately 24 h in decalin and subsequently in chloroform for approximately the same time. After extraction was completed the sample was removed and dried at room temperature then in a vacuum oven (ca. 50 C) to a constant weight. Sol fraction (s) was determined using the following equation
Powdered polypropylene-co-ethylene (CPP) with 2.5 mol% ethylene units, MFR 10 was supplied by Chiso Corporation, Japan. Peletized polybutylene succinate (Bionolle), grade 1010 was received from Showa High Polymer Co. Ltd., Japan. Peletized polypropylene grafted maleic anhydride (Modic) was purchased from Mitsubishi Chemical Co. Ltd., Japan. All materials were used as commercial grade without further puri®cation.
Standard size dumbbell shape samples were irradiated by an electron beam with an energy of 2 MeV and beam current of 1 mA at a dose rate of 10 kGy/pass. The irradiation condition was at room temperature (ca. 20 C) in air.
Fig. 1. Eect of irradiation dose on tensile strength (Ts) and elongation at break (Eb) of uncompatibilized and compatibilized CPP and Bionolle.
Zainuddin et al./Polymer Degradation and Stability 63 (1999) 311±320
Sol fraction s W0 ÿ Wext =W0 and gel fraction (g) was calculated as Gel fraction % 1 ÿ s 100% W0 and Wext denote the weight of the sample before and after extraction, respectively. 2.4. Thermogravimetric (TG) analysis
313
10 C/minute and constant rate of nitrogen gas ¯ow of 50 ml/minute. 2.5. Mechanical properties measurement The elongation at break and tensile strength of the standard size dumbbell shape samples (ASTMD 1822L) were measured using tensiometer Strograph-R1 (Toyoseiki Co. Ltd., Japan) at a crosshead speed of 100 mm/min at ambient temperature (ca. 25 C).
The thermogravimetric weight loss experiment was conducted using a TG analyzer, TGA 50 (Shimadzu). The experiment was performed by heating the sample from room temperature to 500 C at heating rate of
Fig. 3. The dependence of gel fraction on irradiation dose for CPP, Bionolle, and compatibilized CPP/Bionolle blends.
Fig. 2. Eect of irradiation dose on tensile strength (Ts) and elongation at break (Eb) of compatibilized CPP/Bionolle blends.
Fig. 4. Typical Charlesby-Pinner plot for irradiated CPP, Bionolle, and compatibilized CPP/Bionolle blends.
314
Zainuddin et al./Polymer Degradation and Stability 63 (1999) 311±320
2.6. Soil burial test
Weight loss % W0 ÿ Wsoil =W0 100%
The standard size dumbbell shape samples were buried in a soil mixture consisting of 1/3 fermented leaves, 1/3 pond soil, and 1/3 garden soil. The biodegradation test was performed in the laboratory but the soil temperature was not controlled and ¯uctuated from ca. 5 to 27 C (during winter and summer seasons). The moisture content of the soil was maintained ca. 30±40% and pH around 5±6. The sample was removed after 1, 3, 5, and 7 months and washed thoroughly with water and dried at room temperature and subsequently in a vacuum oven at ca. 50 C for at least 24 h. The weight loss was calculated using the following equation
where W0 and Wsoil are the weight of the sample before and after soil burial, respectively. 3. Results and discussion The most dicult thing when a polymeric material or a polyblend is subjected to ionizing radiation is to prevent the negative eect of ionizing radiation while maintaining the desired properties. Some polymers are liable to radiation degradation, and result a decrease in the over all mechanical properties. This case was clearly
Fig. 5. Relationship between gelation dose (Dg, estimated from Fig. 4) and blend composition.
Fig. 6. TGA weight loss on thermal degradation of unirradiated and irradiated compatibilized CPP/Bionolle blends.
Fig. 7. Changes in the tensile strength (Ts) and elongation at break (Eb) during indoor storage (open marks) and soil burial (®lled marks) for unirradiated and irradiated compatibilized Bionolle.
Zainuddin et al./Polymer Degradation and Stability 63 (1999) 311±320
315
observed in the irradiation of CPP and Bionolle. Even at relatively low irradiation dose (D<100 kGy), CPP and Bionolle underwent serious degradation, as indicated by signi®cant reduction in the tensile strength and elongation at break (open rectangular/circle marks in Fig. 1(a)±(d). This deleterious weakness however may be improved by addition of certain reactive groups. From the literature [17±19], it was reported that such groups can transfer and dissipate the energy intermolecularly, thus acting as an energy sink. Fortunately. Modic used in this experiment has a cyclic anhydride group that can play two important roles. The ®rst is to compatibilize CPP and Bionolle, and the second is to act
as an energy sink. The compatibilizing eect was already discussed in the preceding paper [1]. The role of Modic as an energy sink may be evidenced by Fig. 1(a)±(d), ®lled rectangular/circle marks. It was noted that in the presence of Modic (15%), the tensile strength and elongation at break of Bionolle and CPP were signi®cantly improved. Similarly, it may be expected the same eect will also hold in the compatibilized CPP/Bionolle blends. The results presented in Fig. 2(a) and (b) apparently show the fact. The tensile strength and elongation at break of the polyblends were quite stable up to 80 kGy of irradiation dose. There was a little increase even for the sample containing CPP/Bionolle (50/50).
Fig. 8. Changes in the tensile strength (Ts) and elongation at break (Eb) during indoor storage (open marks) and soil burial (®lled marks) for unirradiated and irradiated compatibilized CPP/Bionolle (25/75) blend.
Fig. 9. Changes in the tensile strength (Ts) and elongation at break (Eb) during indoor storage (open marks) and soil burial (®lled marks) for unirradiated and irradiated compatibilized CPP/Bionolle (50/50) blend.
316
Zainuddin et al./Polymer Degradation and Stability 63 (1999) 311±320
In order to discover more about the irradiation eect on the polyblend, sol-gel analysis as well as TGA measurement have been done. As seen in Fig. 3, on increasing the irradiation dose, the gel fraction of the polyblend also increased. It is believed that an increase in the gel fraction is the result of crosslinking but from which component? Since the gel fraction throughout the dose range of 200±400 kGy increases almost proportionally with increasing Bionolle content, the crosslinking is mainly contributed by Bionolle. Moreover, the data presented in Fig. 5 de®nitely con®rmed this major role since the gelation dose (as estimated from the well known Charlesby-Pinner plot, Fig. 4) of CPP was found
Fig. 10. Changes in the tensile strength (Ts) and elongation at break (Eb) during indoor storage (open marks) and soil burial (®lled marks) for unirradiated and irradiated compatibilized CPP/Bionolle (75/25) blend.
to be in®nity. Additionally, as the maximum gel fraction in the polyblend was lower than 50% (Fig. 3) and the ratio of the degradation yield to crosslinking yield, p0/q0 was over 1 (roughly estimated from Fig. 4), the whole process for all blend compositions would be governed by degradation. This dominant process was also supported by TGA data, as presented in Fig. 6. It is seen that the initial weight losses of irradiated polyblends were slightly reduced. As mentioned before, compatibilized Bionolle and CPP/Bionolle blends are quite stable at relatively low irradiation dose. So it was worthwhile to examine the stability of irradiated samples during indoor storage and simultaneously to monitor the mechanical properties and biodegradability in the soil.
Fig. 11. Changes in the tensile strength (Ts) and elongation at break (Eb) during indoor storage (open marks) and soil burial (®lled marks) for unirradiated and irradiated compatibilized CPP.
Zainuddin et al./Polymer Degradation and Stability 63 (1999) 311±320
In the case of compatibilized Bionolle, during indoor storage, the tensile strength and elongation at break were observed to be quite stable for all doses, even up to 5 months [see Fig. 7(a) and (b)]. Actually, this is not surprising because in this specimen, the degradation yield was only a slightly higher compared to the crosslinking yield, as estimated from Fig. 4 (p0/q0 should be between 1 and 1.2). On the other hand, the sample buried in soil clearly displays a signi®cant reduction in the tensile strength and elongation at break (given in the same ®gure), indicating that the biodegradation has occurred. In the case of compatibilized CPP/Bionolle (25/75),
317
stored up to 7 months indoor, the sample irradiated to 20 kGy shows good mechanical stability, as shown in Fig. 8(a) and (b). The tensile strength and elongation at break were still as high as the unaged sample. On the other hand, for the sample irradiated with a dose of 50 or 80 kGy, both tensile strength and elongation at break started to decrease gradually after 5 months (presented in the same ®gure). This reduction is usually believed to be the result of postirradiation oxidation during storage. Meanwhile, the sample buried in soil shows complete loss of strength within 5 months. The extensibility of some samples was already zero within less than 2
Fig. 12. Kinetics of weight loss for unirradiated and irradiated samples during soil burial. O Bionolle; Bionolle+M15%; ! CPP/Bionolle(1/ 3)+M15%; X CPP/Bionelle(3/1)+M15%; ^ CPP/Bionelle(1/1)+M15%; and CPP+M15%, and CPP.
318
Zainuddin et al./Polymer Degradation and Stability 63 (1999) 311±320
months. These sharp changes in the mechanical properties were attributed to microbial attack, although some other factors may also enhance the degradation, such as postirradiation eect, hydrolytic process, and mechanical stress of the soil. In the case of compatibilized CPP/Bionolle (50/50), as depicted in Fig. 9(a) and (b), it is evident that during indoor storage the tensile strength and elongation at break were not stable. Both began to decrease in the following month. This is reasonable because the degradation yield of this sample was about 1.4 times higher than its crosslinking yield. In other words, postirradiation eects will become more pronounced. The sample buried in the soil showed slower degradation than that of CPP/Bionolle (25/75). Certainly, this is not unexpected, since the Bionolle content in this matrix is lower than that of CPP/Bionolle (25/75). From Fig. 10(a) and (b) and 11(a) and (b), it can be seen that the tensile strength and elongation at break of compatibilized CPP/Bionolle (75/25) and compatibilized CPP during indoor storage were very unstable, particularly with the dose of 50 and 80 kGy. They immediately decreased with time. These data suggest that CPP as the major component in the sample stimulates the degradation. Carlsson [20] and Kashiwabara [21] reported that irradiated PP will undergoes postirradiation oxidation during storage. That is why the tensile strength and elongation at break of the CPP-rich samples dropped drastically. From the weight loss data given in Fig. 12 for unirradiated and irradiated samples, it is possible to deduce the biodegradability behavior of the polymer/polyblend. It appears that at the beginning, even if the polymer/
polyblend had no strength, the weight loss was still very low. This suggests that the broken molecular chains resulting from either microbial attack or other factors including postirradiation degradation, were still not simple enough to be digested by microorganisms, and/ or the broken chains are still bound in the network. After three months however, the Bionolle-rich sample clearly shows a signi®cant weight loss. These processes occurred actively until complete weight loss was achieved. In general, the mechanism of weight loss is complicated, but in some cases the solution may follow a simple pattern. As shown in Fig. 12 (solid line), the kinetics of weight loss were satisfactorily described by a parabolic model. Based on this model the time for complete biodegradation (weight loss 100%) (t) has been calculated and plotted against irradiation dose (Fig. 13). It seems that in some cases irradiation may slightly enhance the biodegradation (shortened t), depending on the blend composition, particularly Bionolle content. If the Bionolle content in the polyblend was lower than 40% the biodegradability becomes very low [appears to be asymptotic (Fig. 14). That is why for the compatibilized CPP/Bionolle (75/25), even up to 7 months, the occurrence of biodegradation was still not observable (the weight loss was equal to zero). Again this is because at low Bionolle content, although Bionolle exists as a dispersed phase, it is mostly covered by CPP. As a result, Bionolle is not eciently attacked or removed from the matrix. The compatibilized CPP and pure CPP would not give any weight loss since they are not a ready carbon source for the microbes. The visual observation (photographs) of the unirradiated and irradiated blends after 1, 3, and 5 months
Fig. 13. Eect of irradiation dose on the time for complete biodegradation (t, 100% weight-loss) in soil burial test.
Fig. 14. Eect of Bionolle content on the time for complete biodegradation (t) in soil burial test at dierent irradiation dose.
Zainuddin et al./Polymer Degradation and Stability 63 (1999) 311±320
319
Fig. 15. Photographs of the unirradiated and irradiated samples after biodegradation in soil for 1, 3, and 5 months. (A) Bionolle; (B) Bionolle+M15%; (C) CPP/Bionolle(25/75)+M15%; (D) CPP/Bionolle(50/50)+M15%; and (E) CPP/Bionolle (75/25)+M15%.
of soil burial are presented in Fig. 15. It is evident that after 5 months the physical appearance of the polyblends, particularly compatibilized Bionolle and CPP/Bionolle (25/75) changed very much. Obviously, this is because of the polyblends have been deteriorated/attacked by microorganisms and other environmental factors. In contrast, compatibilized CPP/Bionolle (75/25) blend was observed to remain almost unchanged, indicating that its biodegradability was very low. Additionally, there was no signi®cant dierence between physical appearance of unirradiated and irradiated polyblends.
when the products will be sterilized by ionizing radiation. Furthermore, the mechanical stability of the irradiated CPP/Bionolle blends during indoor storage has been shown to be fairly good, particularly compatibilized Bionolle and CPP/Bionolle (25/75). Furthermore, the biodegradation properties of irradiated polyblend were still as high as the unirradiated ones; in some cases irradiation was even able to enhance the biodegradation slightly.
4. Conclusion
Mr. Zainuddin wishes to thank TRCRE-JAERI for supporting this work and BATAN is gratefully acknowledged for giving him a chance to work at TRCRE-JAERI from November 1996 to August 1997, in the frame work of Bilateral Research Cooperation in the Field of Radiation Processing between CAIRBATAN, Indonesia and TRCRE-JAERI, Japan.
From this experiment it is inferred that, in the presence of Modic, the radiation degradation of the CPP/ Bionolle blend was prevented to some extent, particularly at relatively low irradiation dose (D<100 kGy). This protective eect will be very useful in practical use
Acknowledgements
320
Zainuddin et al./Polymer Degradation and Stability 63 (1999) 311±320
References [1] Zainuddin, Sudradjat A, Razzak M, Yoshii F, Makuuchi K. Polyblend CPP and Bionolle with PP-g-MAH as compatibilizer I: compatibility. J Appl Polym Sci, submitted for publication. [2] Zainuddin, Razzak MT, Yoshii F, Makuuchi K. Polyblend CPP and Bionolle with PP-g-MAH as compatibilizer II: biodegradability. J Appl Polym Sci, submitted for publication. [3] Gisbergen JV, Overbergh N. In: Singh A, Silverman J. editors. Radiation processing of polymers. Munich: Hanser Publication, 1992. p. 51. [4] Spenadel L. Rad Phys Chem 1979;14:683. [5] Garrett RW, Donnel JH, Pomery PJ, Shum EC. J Appl Polym Sci 1979;24:2415. [6] Shultz AR, Mankin GI. J Appl Polym Sci Polym Symp 1976;54:341. [7] Makhlis FA. In: Radiation physics and chemistry of polymers. New York: John Wiley and Sons, 1972. p. 288. [8] Woods RL, Pikaev AK. In: Applied radiation chemistry. Radiation processing. New York: John Wiley and Sons, 1994. p. 341. [9] Ivanov VS. In: Radiation chemistry of polymers. Utrecht, The Netherlands: VSV, 1992. p. 123.
[10] Rizzo G, Spadaro G, Acierno D. Rad Phys Chem 1983;21(4):349. [11] Spadaro G, Rizzo G, Acierno D, Caldero E. Rad Phys Chem 1984;23(4):445. [12] Kostoski D, Babic D, Stojanovic Z, Gal O. Rad Phys Chem 1986;28(3):269. [13] Gorelik BA, Sokolova LA, Grigoriev AG, Koshelev SD, Semenenko EI, Mathiusin GA, Rychla L. Makromol Chem, Macromol Symp 1989;28:249. [14] Nguyen QT, Kausch HH. J Appl Polym Sci 1984;29:455. [15] Thomas S, Gupta BR, De SK. Polym Deg and Stab 1987;18:189. [16] Nishi T, Kwei TK. Polymer 1975;16:285. [17] Scroog CE, Endrey AL, Abramo SV, Berr CE, Edwards WM, Olivier KL. J Polym Sci 1965;A3:1373. [18] Charlesby A. Rad Phys Chem 1977;10:177. [19] Ivanov VS. In: Radiation chemistry of polymers. Utrecht, The Netherlands: VSV, 1992. p. 197. [20] Carlsson DJ, Dobbin CJB, Jensen JPT, Wiles DM. In: Klemchuk, PP. editor. Polymer, stabilization and degradation. Washington, DC: ACS, 1985. p. 359. [21] Kashiwabara H, Seguchi T. In: Singh A, Silverman J. editors. Radiation processing of polymers. Munich: Hanser Publication, 1992. p. 221.
Radiation eect on the mechanical stability and biodegradability of CPP/Bionolle blend Zainuddin a,*, Mirzan Thabrani Razzak a, Fumio Yoshii b, Keizo Makuuchi b a
National Atomic Energy Agency, Center for the Applications of Isotopes and Radiation, Jl. Cinere Pasar Jumat, PO Box 7002 JKSKL, Jakarta 12070, Indonesia b Japan Atomic Energy Research Institute, Takasaki Radiation Chemistry Research Establishment, 1233 Watanuki-machi, Takasaki-shi, Gunma-ken, 370-12 Japan Received 2 March 1998; received in revised form 15 June 1998; accepted 15 July 1998
Abstract Blends of polypropylene-co-ethylene (CPP) and polybutylene succinate (Bionolle) with polypropylene grafted maleic anhydride (Modic) as a compatibilizer were prepared by melt blending. Irradiation of the resultant polyblend was carried out using an electron beam in air. It was noted that the Modic compatibilizer also appears to act as a protective agent toward radiation degradation. The occurrence of crosslinking in the polyblend was observed, mainly contributed by Bionolle. However the whole process over all blend composition ranges was dominated by degradation. During indoor storage, the mechanical stability of irradiated polyblends was found to be fairly good, particularly compatibilized Bionolle and CPP/Bionolle (27/75). On the other hand, the sample buried in soil showed a drastic reduction in the over all mechanical properties. The extent of biodegradability as estimated from the weight loss increased with increasing Bionolle content. A synergistic eect on the weight loss was shown by compatibilized Bionolle and CPP/Bionolle (25/75). Additionally, even if the sample was no longer strong due to postirradiation degradation, the biodegradability of the polyblend was not much improved. Using a curve ®t model the time for complete weight loss was found to be approximately 14, 8, 7, and 12 months for unirradiated and irradiated Bionolle, compatibilized Bionolle, CPP/Bionolle (25/75) and (50/50), respectively. # 1999 Elsevier Science Ltd. All rights reserved.
1. Introduction To preserve the environment from harmful impact of solid waste plastic, synthesizing biodegradable plastics is highly in demand. For this purpose various approaches have been considered and were reported in our previous paper [1]. Melt-blending non-biodegradable and biodegradable polymer seems to be the best choice to manufacture biodegradable polyblends in the future. In the ®rst paper [1], we have reported the blending conditions and the optimum concentration of compatibilizer to obtain true molecular compatibility in the CPP/Bionolle blend over a wide composition range. In a second paper [2], we have discussed the biodegradability of Bionolle and its blend in two biotic environments, lipase-enzyme solution and soil burial. Nowadays, utilization of high energy radiation (gamma or electron beam) is commonplace in the mod* Corresponding author.
i®cation of polymers. As a result, numerous extensive studies on the irradiation of single polymers have been reported elsewhere. However, few studies have been made on the eect of irradiation on polyblends [3±6]. Irradiation of polyblends is generally aimed at introducing a desired amount of crosslinking or chain scission. Crosslinking will bring about an increase in tensile strength, elongation, modulus of elasticity, hardness, and softening temperature. On the other hand, chain scission decreases these properties [7±9]. The eects of gamma irradiation on mechanical properties and structure (crystallinity and density) of LDPE-iPP blend have been studied by Rizzo and his coworkers [10,11], and Kostoski [12]. The changes in physico-mechanical properties and thermostability of gamma irradiated PEPP blends have been elucidated by Gorelik [13]. The protective eects of vinyl groups in gamma irradiated PMMA±SAN and PMMA±PS blends have been reported by Nguyen [14]. The other eect, e.g. surface morphology and failure behavior of an irradiated polyblend were studied by Thomas [15], using PP±EVA blends.
0141-3910/99/$Ðsee front matter # 1999 Elsevier Science Ltd. All rights reserved PII: S0141 -3 910(98)00111 -6
312
Zainuddin et al./Polymer Degradation and Stability 63 (1999) 311±320
Nishi [16] studied the eect of electron beam irradiation on the cloud point behavior of PS±PVME system. In the current paper, we present our study in the radiation eect on the mechanical properties and biodegradability of compatibilized CPP/Bionolle blend.
2.2. Irradiation of the sample
2. Experimental
2.3. Sol-gel analysis
2.1. Materials
To remove the uncrosslinked or soluble part (sol fraction), the irradiated sample was extracted by using a suitable solvent. To dissolve CPP in the blends, decalin was used and chloroform for Bionolle. The extraction was done for approximately 24 h in decalin and subsequently in chloroform for approximately the same time. After extraction was completed the sample was removed and dried at room temperature then in a vacuum oven (ca. 50 C) to a constant weight. Sol fraction (s) was determined using the following equation
Powdered polypropylene-co-ethylene (CPP) with 2.5 mol% ethylene units, MFR 10 was supplied by Chiso Corporation, Japan. Peletized polybutylene succinate (Bionolle), grade 1010 was received from Showa High Polymer Co. Ltd., Japan. Peletized polypropylene grafted maleic anhydride (Modic) was purchased from Mitsubishi Chemical Co. Ltd., Japan. All materials were used as commercial grade without further puri®cation.
Standard size dumbbell shape samples were irradiated by an electron beam with an energy of 2 MeV and beam current of 1 mA at a dose rate of 10 kGy/pass. The irradiation condition was at room temperature (ca. 20 C) in air.
Fig. 1. Eect of irradiation dose on tensile strength (Ts) and elongation at break (Eb) of uncompatibilized and compatibilized CPP and Bionolle.
Zainuddin et al./Polymer Degradation and Stability 63 (1999) 311±320
Sol fraction s W0 ÿ Wext =W0 and gel fraction (g) was calculated as Gel fraction % 1 ÿ s 100% W0 and Wext denote the weight of the sample before and after extraction, respectively. 2.4. Thermogravimetric (TG) analysis
313
10 C/minute and constant rate of nitrogen gas ¯ow of 50 ml/minute. 2.5. Mechanical properties measurement The elongation at break and tensile strength of the standard size dumbbell shape samples (ASTMD 1822L) were measured using tensiometer Strograph-R1 (Toyoseiki Co. Ltd., Japan) at a crosshead speed of 100 mm/min at ambient temperature (ca. 25 C).
The thermogravimetric weight loss experiment was conducted using a TG analyzer, TGA 50 (Shimadzu). The experiment was performed by heating the sample from room temperature to 500 C at heating rate of
Fig. 3. The dependence of gel fraction on irradiation dose for CPP, Bionolle, and compatibilized CPP/Bionolle blends.
Fig. 2. Eect of irradiation dose on tensile strength (Ts) and elongation at break (Eb) of compatibilized CPP/Bionolle blends.
Fig. 4. Typical Charlesby-Pinner plot for irradiated CPP, Bionolle, and compatibilized CPP/Bionolle blends.
314
Zainuddin et al./Polymer Degradation and Stability 63 (1999) 311±320
2.6. Soil burial test
Weight loss % W0 ÿ Wsoil =W0 100%
The standard size dumbbell shape samples were buried in a soil mixture consisting of 1/3 fermented leaves, 1/3 pond soil, and 1/3 garden soil. The biodegradation test was performed in the laboratory but the soil temperature was not controlled and ¯uctuated from ca. 5 to 27 C (during winter and summer seasons). The moisture content of the soil was maintained ca. 30±40% and pH around 5±6. The sample was removed after 1, 3, 5, and 7 months and washed thoroughly with water and dried at room temperature and subsequently in a vacuum oven at ca. 50 C for at least 24 h. The weight loss was calculated using the following equation
where W0 and Wsoil are the weight of the sample before and after soil burial, respectively. 3. Results and discussion The most dicult thing when a polymeric material or a polyblend is subjected to ionizing radiation is to prevent the negative eect of ionizing radiation while maintaining the desired properties. Some polymers are liable to radiation degradation, and result a decrease in the over all mechanical properties. This case was clearly
Fig. 5. Relationship between gelation dose (Dg, estimated from Fig. 4) and blend composition.
Fig. 6. TGA weight loss on thermal degradation of unirradiated and irradiated compatibilized CPP/Bionolle blends.
Fig. 7. Changes in the tensile strength (Ts) and elongation at break (Eb) during indoor storage (open marks) and soil burial (®lled marks) for unirradiated and irradiated compatibilized Bionolle.
Zainuddin et al./Polymer Degradation and Stability 63 (1999) 311±320
315
observed in the irradiation of CPP and Bionolle. Even at relatively low irradiation dose (D<100 kGy), CPP and Bionolle underwent serious degradation, as indicated by signi®cant reduction in the tensile strength and elongation at break (open rectangular/circle marks in Fig. 1(a)±(d). This deleterious weakness however may be improved by addition of certain reactive groups. From the literature [17±19], it was reported that such groups can transfer and dissipate the energy intermolecularly, thus acting as an energy sink. Fortunately. Modic used in this experiment has a cyclic anhydride group that can play two important roles. The ®rst is to compatibilize CPP and Bionolle, and the second is to act
as an energy sink. The compatibilizing eect was already discussed in the preceding paper [1]. The role of Modic as an energy sink may be evidenced by Fig. 1(a)±(d), ®lled rectangular/circle marks. It was noted that in the presence of Modic (15%), the tensile strength and elongation at break of Bionolle and CPP were signi®cantly improved. Similarly, it may be expected the same eect will also hold in the compatibilized CPP/Bionolle blends. The results presented in Fig. 2(a) and (b) apparently show the fact. The tensile strength and elongation at break of the polyblends were quite stable up to 80 kGy of irradiation dose. There was a little increase even for the sample containing CPP/Bionolle (50/50).
Fig. 8. Changes in the tensile strength (Ts) and elongation at break (Eb) during indoor storage (open marks) and soil burial (®lled marks) for unirradiated and irradiated compatibilized CPP/Bionolle (25/75) blend.
Fig. 9. Changes in the tensile strength (Ts) and elongation at break (Eb) during indoor storage (open marks) and soil burial (®lled marks) for unirradiated and irradiated compatibilized CPP/Bionolle (50/50) blend.
316
Zainuddin et al./Polymer Degradation and Stability 63 (1999) 311±320
In order to discover more about the irradiation eect on the polyblend, sol-gel analysis as well as TGA measurement have been done. As seen in Fig. 3, on increasing the irradiation dose, the gel fraction of the polyblend also increased. It is believed that an increase in the gel fraction is the result of crosslinking but from which component? Since the gel fraction throughout the dose range of 200±400 kGy increases almost proportionally with increasing Bionolle content, the crosslinking is mainly contributed by Bionolle. Moreover, the data presented in Fig. 5 de®nitely con®rmed this major role since the gelation dose (as estimated from the well known Charlesby-Pinner plot, Fig. 4) of CPP was found
Fig. 10. Changes in the tensile strength (Ts) and elongation at break (Eb) during indoor storage (open marks) and soil burial (®lled marks) for unirradiated and irradiated compatibilized CPP/Bionolle (75/25) blend.
to be in®nity. Additionally, as the maximum gel fraction in the polyblend was lower than 50% (Fig. 3) and the ratio of the degradation yield to crosslinking yield, p0/q0 was over 1 (roughly estimated from Fig. 4), the whole process for all blend compositions would be governed by degradation. This dominant process was also supported by TGA data, as presented in Fig. 6. It is seen that the initial weight losses of irradiated polyblends were slightly reduced. As mentioned before, compatibilized Bionolle and CPP/Bionolle blends are quite stable at relatively low irradiation dose. So it was worthwhile to examine the stability of irradiated samples during indoor storage and simultaneously to monitor the mechanical properties and biodegradability in the soil.
Fig. 11. Changes in the tensile strength (Ts) and elongation at break (Eb) during indoor storage (open marks) and soil burial (®lled marks) for unirradiated and irradiated compatibilized CPP.
Zainuddin et al./Polymer Degradation and Stability 63 (1999) 311±320
In the case of compatibilized Bionolle, during indoor storage, the tensile strength and elongation at break were observed to be quite stable for all doses, even up to 5 months [see Fig. 7(a) and (b)]. Actually, this is not surprising because in this specimen, the degradation yield was only a slightly higher compared to the crosslinking yield, as estimated from Fig. 4 (p0/q0 should be between 1 and 1.2). On the other hand, the sample buried in soil clearly displays a signi®cant reduction in the tensile strength and elongation at break (given in the same ®gure), indicating that the biodegradation has occurred. In the case of compatibilized CPP/Bionolle (25/75),
317
stored up to 7 months indoor, the sample irradiated to 20 kGy shows good mechanical stability, as shown in Fig. 8(a) and (b). The tensile strength and elongation at break were still as high as the unaged sample. On the other hand, for the sample irradiated with a dose of 50 or 80 kGy, both tensile strength and elongation at break started to decrease gradually after 5 months (presented in the same ®gure). This reduction is usually believed to be the result of postirradiation oxidation during storage. Meanwhile, the sample buried in soil shows complete loss of strength within 5 months. The extensibility of some samples was already zero within less than 2
Fig. 12. Kinetics of weight loss for unirradiated and irradiated samples during soil burial. O Bionolle; Bionolle+M15%; ! CPP/Bionolle(1/ 3)+M15%; X CPP/Bionelle(3/1)+M15%; ^ CPP/Bionelle(1/1)+M15%; and CPP+M15%, and CPP.
318
Zainuddin et al./Polymer Degradation and Stability 63 (1999) 311±320
months. These sharp changes in the mechanical properties were attributed to microbial attack, although some other factors may also enhance the degradation, such as postirradiation eect, hydrolytic process, and mechanical stress of the soil. In the case of compatibilized CPP/Bionolle (50/50), as depicted in Fig. 9(a) and (b), it is evident that during indoor storage the tensile strength and elongation at break were not stable. Both began to decrease in the following month. This is reasonable because the degradation yield of this sample was about 1.4 times higher than its crosslinking yield. In other words, postirradiation eects will become more pronounced. The sample buried in the soil showed slower degradation than that of CPP/Bionolle (25/75). Certainly, this is not unexpected, since the Bionolle content in this matrix is lower than that of CPP/Bionolle (25/75). From Fig. 10(a) and (b) and 11(a) and (b), it can be seen that the tensile strength and elongation at break of compatibilized CPP/Bionolle (75/25) and compatibilized CPP during indoor storage were very unstable, particularly with the dose of 50 and 80 kGy. They immediately decreased with time. These data suggest that CPP as the major component in the sample stimulates the degradation. Carlsson [20] and Kashiwabara [21] reported that irradiated PP will undergoes postirradiation oxidation during storage. That is why the tensile strength and elongation at break of the CPP-rich samples dropped drastically. From the weight loss data given in Fig. 12 for unirradiated and irradiated samples, it is possible to deduce the biodegradability behavior of the polymer/polyblend. It appears that at the beginning, even if the polymer/
polyblend had no strength, the weight loss was still very low. This suggests that the broken molecular chains resulting from either microbial attack or other factors including postirradiation degradation, were still not simple enough to be digested by microorganisms, and/ or the broken chains are still bound in the network. After three months however, the Bionolle-rich sample clearly shows a signi®cant weight loss. These processes occurred actively until complete weight loss was achieved. In general, the mechanism of weight loss is complicated, but in some cases the solution may follow a simple pattern. As shown in Fig. 12 (solid line), the kinetics of weight loss were satisfactorily described by a parabolic model. Based on this model the time for complete biodegradation (weight loss 100%) (t) has been calculated and plotted against irradiation dose (Fig. 13). It seems that in some cases irradiation may slightly enhance the biodegradation (shortened t), depending on the blend composition, particularly Bionolle content. If the Bionolle content in the polyblend was lower than 40% the biodegradability becomes very low [appears to be asymptotic (Fig. 14). That is why for the compatibilized CPP/Bionolle (75/25), even up to 7 months, the occurrence of biodegradation was still not observable (the weight loss was equal to zero). Again this is because at low Bionolle content, although Bionolle exists as a dispersed phase, it is mostly covered by CPP. As a result, Bionolle is not eciently attacked or removed from the matrix. The compatibilized CPP and pure CPP would not give any weight loss since they are not a ready carbon source for the microbes. The visual observation (photographs) of the unirradiated and irradiated blends after 1, 3, and 5 months
Fig. 13. Eect of irradiation dose on the time for complete biodegradation (t, 100% weight-loss) in soil burial test.
Fig. 14. Eect of Bionolle content on the time for complete biodegradation (t) in soil burial test at dierent irradiation dose.
Zainuddin et al./Polymer Degradation and Stability 63 (1999) 311±320
319
Fig. 15. Photographs of the unirradiated and irradiated samples after biodegradation in soil for 1, 3, and 5 months. (A) Bionolle; (B) Bionolle+M15%; (C) CPP/Bionolle(25/75)+M15%; (D) CPP/Bionolle(50/50)+M15%; and (E) CPP/Bionolle (75/25)+M15%.
of soil burial are presented in Fig. 15. It is evident that after 5 months the physical appearance of the polyblends, particularly compatibilized Bionolle and CPP/Bionolle (25/75) changed very much. Obviously, this is because of the polyblends have been deteriorated/attacked by microorganisms and other environmental factors. In contrast, compatibilized CPP/Bionolle (75/25) blend was observed to remain almost unchanged, indicating that its biodegradability was very low. Additionally, there was no signi®cant dierence between physical appearance of unirradiated and irradiated polyblends.
when the products will be sterilized by ionizing radiation. Furthermore, the mechanical stability of the irradiated CPP/Bionolle blends during indoor storage has been shown to be fairly good, particularly compatibilized Bionolle and CPP/Bionolle (25/75). Furthermore, the biodegradation properties of irradiated polyblend were still as high as the unirradiated ones; in some cases irradiation was even able to enhance the biodegradation slightly.
4. Conclusion
Mr. Zainuddin wishes to thank TRCRE-JAERI for supporting this work and BATAN is gratefully acknowledged for giving him a chance to work at TRCRE-JAERI from November 1996 to August 1997, in the frame work of Bilateral Research Cooperation in the Field of Radiation Processing between CAIRBATAN, Indonesia and TRCRE-JAERI, Japan.
From this experiment it is inferred that, in the presence of Modic, the radiation degradation of the CPP/ Bionolle blend was prevented to some extent, particularly at relatively low irradiation dose (D<100 kGy). This protective eect will be very useful in practical use
Acknowledgements
320
Zainuddin et al./Polymer Degradation and Stability 63 (1999) 311±320
References [1] Zainuddin, Sudradjat A, Razzak M, Yoshii F, Makuuchi K. Polyblend CPP and Bionolle with PP-g-MAH as compatibilizer I: compatibility. J Appl Polym Sci, submitted for publication. [2] Zainuddin, Razzak MT, Yoshii F, Makuuchi K. Polyblend CPP and Bionolle with PP-g-MAH as compatibilizer II: biodegradability. J Appl Polym Sci, submitted for publication. [3] Gisbergen JV, Overbergh N. In: Singh A, Silverman J. editors. Radiation processing of polymers. Munich: Hanser Publication, 1992. p. 51. [4] Spenadel L. Rad Phys Chem 1979;14:683. [5] Garrett RW, Donnel JH, Pomery PJ, Shum EC. J Appl Polym Sci 1979;24:2415. [6] Shultz AR, Mankin GI. J Appl Polym Sci Polym Symp 1976;54:341. [7] Makhlis FA. In: Radiation physics and chemistry of polymers. New York: John Wiley and Sons, 1972. p. 288. [8] Woods RL, Pikaev AK. In: Applied radiation chemistry. Radiation processing. New York: John Wiley and Sons, 1994. p. 341. [9] Ivanov VS. In: Radiation chemistry of polymers. Utrecht, The Netherlands: VSV, 1992. p. 123.
[10] Rizzo G, Spadaro G, Acierno D. Rad Phys Chem 1983;21(4):349. [11] Spadaro G, Rizzo G, Acierno D, Caldero E. Rad Phys Chem 1984;23(4):445. [12] Kostoski D, Babic D, Stojanovic Z, Gal O. Rad Phys Chem 1986;28(3):269. [13] Gorelik BA, Sokolova LA, Grigoriev AG, Koshelev SD, Semenenko EI, Mathiusin GA, Rychla L. Makromol Chem, Macromol Symp 1989;28:249. [14] Nguyen QT, Kausch HH. J Appl Polym Sci 1984;29:455. [15] Thomas S, Gupta BR, De SK. Polym Deg and Stab 1987;18:189. [16] Nishi T, Kwei TK. Polymer 1975;16:285. [17] Scroog CE, Endrey AL, Abramo SV, Berr CE, Edwards WM, Olivier KL. J Polym Sci 1965;A3:1373. [18] Charlesby A. Rad Phys Chem 1977;10:177. [19] Ivanov VS. In: Radiation chemistry of polymers. Utrecht, The Netherlands: VSV, 1992. p. 197. [20] Carlsson DJ, Dobbin CJB, Jensen JPT, Wiles DM. In: Klemchuk, PP. editor. Polymer, stabilization and degradation. Washington, DC: ACS, 1985. p. 359. [21] Kashiwabara H, Seguchi T. In: Singh A, Silverman J. editors. Radiation processing of polymers. Munich: Hanser Publication, 1992. p. 221.