CHEMICAL ENGINEERING TRANSACTIONS  
 

VOL. 63, 2018 

A publication of 

 

The Italian Association 
of Chemical Engineering 
Online at www.aidic.it/cet 

Guest Editors: Jeng Shiun Lim, Wai Shin Ho, Jiří J. Klemeš 
Copyright © 2018, AIDIC Servizi S.r.l. 
ISBN 978-88-95608-61-7; ISSN 2283-9216 

The Effect of Electron Beam Radiation on Mechanical 

Stability of Polybutylene Succinate Polymer 

Munirah Onn
a,

*, Siti N. A. Zaiton
a
, Zarith S. Othman

b
, Faizal A. Rahman

c
, Khairul 

Z. M. Dahlan
a
 

a
Faculty of Applied Sciences, University Technology MARA, Jalan Purnama, Bandar Seri Alam, 81750 Masai, Johor, 

Malaysia 
b
Faculty of Computer and Mathematical Sciences, University Technology MARA, Jalan Purnama, Bandar Seri Alam, 81750 

 Masai, Johor, Malaysia 
c
Radiation Processing Technology Division, Malaysian Institute for Nuclear Technology Research (MINT), Bangi, 43000 

 Kajang, Malaysia 

 munirah591@johor.uitm.edu.my 

This paper examines the effect of electron beam (EB) radiation on mechanical stability of polybutylene 

succinate (PBS) blends with three types of cross linking agent has been studied using tensile, flexural, impact, 

gel content, melt flow index (MFI) and heat deflection temperature (HDT). PBS was radiated using a 3.0MeV 

electron beam machine with doses ranging from 0 to 120 kGy/ 10 kGy per pass. The results show that 20 kGy 

depict the most stable mechanical properties. Higher radiation figures higher crosslink density but depicts 

reduction in most of mechanical properties. Blends with crosslinker such as Triallyl Isocyanurate (TAIC), 

Hexanediol Diacrylate (HDDA) and Tripropyleneglycol Diacrylate (TPGDA) influences the radiated PBS 

properties. PBS/HDDA blends with 20 kGy dose shows the highest in mechanical stability of this type of 

biodegradable resin. The surface morphology study and mechanical values have been used to correlate 

change in the structure of PBS upon degration. 

1. Introduction 

The crosslinking structure in the polymer can be effectively formed by EB radiation. Ionizing radiation 

produces an excitation of polymer molecules in the vicinity of the impinging radiation. The energies associated 

with the excitation are dependent on the irradiation dosage and voltage (velocity) of electrons. The interaction 

results in the formation of free radicals formed by dissociation of molecules in the excited state or by the 

interaction of molecular ions. The free radicals or molecular ions can react by connecting the polymer chains 

directly or initiating grafting reactions. EB radiation resulted in uniformly cured due to the full depth penetration 

of the electrons (Boye, 2008).Radiation of thermoplastic is generally aimed at introducing the desired amount 

of crosslinking or chain scission between reactive polymer molecules. 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. Therefore, to find the optimum radiation dose is 

important to prevent further degradation. Chain scission during radiation can be prevented by addition of 

certain reactive groups because the reactive groups can transfer and dissipate the energy intermolecularly 

thus acting as an energy sink (Zainuddin et al., 1999). PBS is a type of aliphatic polyester that can be 

efficiently synthesized through condensation polymerization from the starting materials of succinic acid and 

butan-1,4-diol. It is a white crystalline thermoplastic polymer with a melting point around 90–120 °C (similar to 

LDPE), glass transition temperature of about -45 to -10 °C (between PE and PP), a tensile strength between 

PE and PP, and stiffness between LDPE and HDPE. PBS has excellent processing capabilities and can be 

processed on polyolefin processing machines at temperatures of 160–200 °C, into various products, such as 

injected, laminated, foamed, extruded and blown ones. It is a biodegradable plastic that has been carried out 

in order to overcome the environmental problems associated with synthetic plastic waste. Like a cellulose and 

paper, PBS is stable in the atmosphere but biodegradable in compost, wet soil, fresh water, seawater and 

                               
 
 

 

 
   

                                                  
DOI: 10.3303/CET1863134

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

Please cite this article as: Munirah Onn, Siti N. A. Zaiton, Zarith S. Othman, Faizal A. Rahman, Khairul Z. M. Dahlan, 2018, The effect of 
electron beam radiation on mechanical stability of polybutylene succinate polymer, Chemical Engineering Transactions, 63, 799-804  
DOI:10.3303/CET1863134   

799



activated sludge where microorganisms are presented. The crosslinking agents added into polymers can 

promote crosslinking over degradation process hence can enhance the strength of the materials. The 

presence of TMPTA, HDDA and TAIC as coagents are commonly used for radiation-induced crosslinking of 

polymers. Conversely, by EB-initiation, TPGDA appears clearly to be more reactive than HDDA, with an initial 

polymerization rate twice as large as that of HDDA. Meanwhile, TAIC/nylon6 blends has reported can be 

radiated further until 400 kGy optimum dose (Rytlewski, et. al. 2010). However, their performance might be the 

difference since the compatibility between the polymers is much more important. The aim of this article is to 

find the optimum radiation dose and provide the information regarding the influences of three types of 

crosslinker upon the radiated PBS resin. The product is expected to solve the environmental issue on current 

non-biodegradable plastic whilst enhancing the properties of PBS. 

2. Materials and methods 

2.1 Materials 

Pelletized polybutylene succinate (PBS) Bionolle, grade 1010 was received from Showa High Polymer Co. 

Ltd., Japan. Chloroform (R&M Marketing Essex, UK) analytical grade was used. Hexanediol Diacrylate 

(HDDA) from Bayer, Germany, Triallyl Isocyanurate (TAIC) (Sigma Aldrich GmbH, Germany) and 

Tripropyleneglycol Diacrylate (TPGDA) from (R&M Marketing Essex, UK) were used as received. 

2.2 Blending and sample preparation 

The blends were prepared using Brabender Plastograph machine rotating at a speed of 50 rpm at temperature 

115°C. For addition with cross-linking agents, only one dose was used which is 20 kGy. These cross-linkers 

were mix by wetting process first before process into the Brabender Mixer. The amount was varied with 0.5,1 

and 2 % (w/w) using the same parameter. The process was conducted for 10 minutes and torque versus time 

curve for every blend was recorded. The blend samples then compress for 5minutes into sheets at 130°C. 

Samples for Flexural and impact test was using stainless steel mold (15 cm × 15 cm × 0.3 cm). For tensile 

test, a stainless-steel mold (15 cm × 15 cm × 0.1 cm) was used. All molded samples were cut into 7 standard 

test pieces using a Wallace die cutter. 

2.3 Radiation of the sample 

Radiation of the samples was carried out at Alutron Department, Malaysia Nuclear Agency. The molded 

sheets were placed in an aluminum container on a conveyor which able to move with a precisely controlled 

speed. The conveyor speed determined the radiation dose absorbed by the samples. During a single crossing 

of radiation zone, the samples absorbed a dose rate of 10 kGy per pass. The successive crossing of radiation 

zone caused an increase in the dose absorbed by the samples by the next 10 kGy. This way, the doses of 0, 

10, 20, 40, 60, 80, 100, 120 and140 kGy were applied to the samples. The doses were controlled by a 

calorimetric method. All samples were irradiated with energy of 3 MeV and beam current of 5mA. After 

radiation, the tensile, flexural and impact were done to find the optimum curing doses for PBS. After the 

optimum dosage was determined, the process of blending was repeated by adding with different crosslinking 

agents. 

2.4 Scanning electron microscopy 

The morphology of the sample surface was investigated with high-resolution scanning electron microscopy 

(SEM), operated at an acceleration voltage of 20 kV and a working distance of 8-12mm. Electron micrographs 

were obtained on samples collected before and after biodegradation testing in soil (1 month). The morphology 

of the sample surfaced was examined using Quanta400. Prior to measurement, the specimens were coated 

with gold (purity, 99.9 %) in order to prevent electrical discharge. 

2.5 Physical testing 

Mechanical properties of the radiated sheet were tested on their tensile, flexural, melt flow index (MFI), heat 

deflection temperature (HDT) and impact strength. Tensile properties were measured using Toyoseiki with 

1kN and crosshead speed of 10mm/min according to ASTMD 1822. Flexural properties were measured using 

Instron Universal Testing Machine 4301. The specimens were 12.7 mm wide and 1kN load was used. Three-

point bending tests were performed with a span length of 43 mm at a crosshead speed of 1.3 mm/min 

referring to ASTMD 790. Izod impact strength notched with 2.54mm was done according to ASTMD 256. The 

specimen is held with a vertical cantilever beam and is broken by a single swing using 1J energy by the 

pendulum at a fix distance. HDT was carried out using Rayran HDT Vicat Softening Point according to 

ASTMD 648. Lastly, for MFI, temperature 190°C with load 2.16kg was done referring to ASTMD 1238. 

800



3. Results and findings 

3.1 Optimum radiation dose for polybutylene succinate 

The optimum dose was determined by EB radiation at a dose range of 10–140 kGy. Upon radiation, the 

reactive group which is ester will undergo predominantly a crosslinking process and, as a result, a three-

dimensional network of polymer chains is formed. Increase radiation dose will increase the crosslinking 

density marginally (Piah et al, 2016). The higher crosslink made the molecule become bigger and as a result, 

a stiffer and brittle sample was observed. The mechanical properties result for the dose range of 0–140 kGy 

are shown in Table 1. The optimum radiation dose at 20 kGy is confirmed by elongation at break, tensile 

strength, and impact strength. After radiation, elongation, tensile strength and Impact strength were improved 

until 20kGy followed by dramatically decrease at a higher dose. Intensive chain scission induced by radiation 

at above 20kGy reduce the length of PBS macro molecules hence result in decreasing in all mechanical 

stability test. The tensile strength of EB radiated PBS at low radiation dose slightly increased due to the 

formation of additional cross-linking in PBS from the production of mainly polymer radicals and hydrogen 

radicals. Increasing radiation dose also influenced the mechanical energy absorbed before fracture. For dose 

20 kGy and above, the PBS has developed more crosslink in their microstructure but significantly alter the 

viscoelastic properties. Above 20 kGy, PBS exhibit brittle behaviors which reduce toughness to resist shock 

impact. Elongation shows a dramatic drop and tensile strength reduce marginally. It illustrates that higher 

radiation dose changes the structure of the sample by exhibit lower strain and brittleness. Thus, it can be 

concluded that PBS reached an optimum level at the radiation dose of 20 kGy.  The dose with the most stable 

mechanical properties was chosen and added with the crosslinking agent. 

Table 1: Effect of electron beam radiation on biodegradable plastic (PBS) 

Dose 

(kGy) 

Melt Flow 

Index 

(g/sec) 

Elongation at 

break 

(%) 

Tensile 

Strenght (MPa) 

Tensile 

Modulus 

(MPa) 

Impact 

Strength (J/M) 

0 9.4 

(0.26) 

388.6 

(11.2) 

37.441 

(1) 

166.72 (3.91) 92.88  

(1.4) 

10 9.9 

(0.154) 

431.67 

(5.4) 

37.95 

(1.59) 

179.905 

(4.91) 

92.9 

 (0.89) 

20 10.16 

(0.23) 

450 

(4.49) 

38.072 

(0.7) 

184.48 

(6.9) 

97.96 

 (1.01) 

40 12.2 

(0.273) 

55.71 

(1.94) 

37.11 

(0.49) 

167.13 

(12.3) 

91.73 

 (1.9) 

60 13.05 

(0.28) 

40 

(3.9) 

38.28 

(1.1) 

164.71 

(17) 

89.2 

 (2.34) 

80 13.4 

(0.21) 

32.86 

(3.53) 

37.4 

(1.25) 

169.6 

(12.04) 

80.42 

 (2.91) 

100 14.2 

(0.259) 

28.57 

(5.5) 

36.65 

(2.8) 

164.91 

(13.4) 

75.63 

 (2.31) 

120 14 

(0.22) 

25.71 

(2.94) 

34.52 

(2.19) 

161.089 

(11.8) 

73.41 

 (2.09) 

140 13.6 

(0.31) 

28 

(6.7) 

35.316 

(3.21) 

161.816 

(16.1) 

73.38 

 (2.86) 

 

During crosslinking reaction, the average molecular weight of the chain increase thus causing a drop in melt 

flow. Table 1, depict the dramatic increment for melt flow index at 120 kGy figures that the reductions of PBS 

molecular weight. Intensive chain scission induced by irradiation at above 120 kGy reduces the length of 

macromolecules thus causing the drop in molecular weight. Degraded materials would generally flow more as 

a result of reduced in physical properties. Even if the chain already break, there is some bonding between the 

chain itself which reducing the movement of the molecule and make restriction of the flow. 

3.2 Effect of crosslinking agent loading on mechanical properties 

Crosslink density is a measure of the total links between chains in a given mass of material. Crosslinking was 

carried out through three types of crosslinking agent which is a molecule of two (TPGDA) and (HDDA) and 

molecules of three (TAIC) that are capable of reacting with the functional groups in the PBS chain (Capek, 
1999). Contribution of crosslinking agent to increase crosslink density and mechanical properties were 

determined by Table 2. It shows that higher addition of crosslinking agent resulted in higher crosslink density 

(Ratnam, 2000).  However, too much crosslinking may also lower the strain induced crystallization process. 
It is generally known that tensile strength and elongation at break depend on the degree of the strain-induced 

801



crystallization, which in turn depends on the polymer chain length and the degree of cross linking. Table 2 

depict that the dynamic mechanical properties obtained with increasing difunctional monomer HDDA content 

attributed to the acceleration of radiation induced crosslinking of the biodegradable plastic and proved that the 

blend are compatible. Whereas for TAIC, 1 % content showed the maximum amount of crosslink density 

which PBS could achieve. The increments of TAIC content only will only cause surface blooming and the 

excessiveness lead to lower mechanical properties. The surface morphology from Figures 1a depicts some of 

the TAIC powder which is immiscible during the blend. The high reactiveness of TAIC also lead to 

incompatibility since the functionality in the PBS is low. Therefore, it was enhancing the shrinkage process 

which yields to internal stresses and is responsible for the observed curling on flexible substrates. The TAIC 

was also reported can absorb acceleration until 100 kGy whereas the optimum dose for PBS is only 20 kGy 

(Piah, 2016). Aromatic parts of TAIC also alter the flexible thermoplastic PBS into a hard-brittle thermoset 

PBS. Therefore, the product will not melt and cannot be recycled. Consequently, when the composition of 

HDDA was increased, all the mechanical properties also increased. The same trend showed for TPGDA. The 

main factor to the value is the form of additives. TPGDA and HDDA are in liquid form whereas TAIC in fine 

powder form. The incorporation of liquid in PBS blend is more miscible and it can be proof from Figure 1a and 

b. Besides, HDDA and TPGDA are aliphatic difunctional monomers, they were more compatible with aliphatic 

polyester chain thus lead to better mechanical performances. Radiation creates free radical in the PBS chain 

and initiates crosslinking of the biopolymers. The reactive diluents like HDDA and TPGDA were used to 

absorb the radiation beam in order to generate free radicals that initiate the crosslinking network (Rytlewski et 

al, 2010).   The improvement in mechanical strength properties proved the presence of unsaturation from an 

acrylic group was attached at the end of aliphatic polyester backbone chain. The increment in elongation 

proved that they impart more ductility but since the modulus shows a reduction, it became softer and the 

reduction in flexural strength depicts that the resistance toward bending stress is becoming lower due to the 

lower modulus. Therefore, the decrease in modulus has reduced it stiffness hence effect the sample surface 

tension.  

Table 2. Effect of crosslinking agents on biodegradable plastic (PBS) mechanical properties 

Formulation Impact 

(J/M) 

Elongation 

(%) 

Tensile 

Modulus 

(MPa) 

Tensile 

Strength 

(MPa) 

Flexural 

Strength 

(MPa) 

Flexural 

Modulus 

(MPa) 

HDT 

(°C) 

PBS 92.88(2.3) 388.6(11) 166.7(3.19) 37.4(1) 44.45(0.7) 615.4(11.5) 97.4(1.3) 

0.5 %TAIC 115.5(1.2) 394.3(4.8) 159.7(0.95) 38.9(1) 46.6(0.2) 645.7(5.6) 98.7(0.9) 

1 %TAIC 88.3(2.5) 236.7(4.7) 160.8(9.4) 38.9(0.81) 43.93(0.8) 600.85(10) 101.5(0.7) 

2 %TAIC 84.29(3.7) 171.1(1.6) 164.4(11) 36.5(0.98) 43.14(2.4) 606(25.6) 97.8(0.6) 

0.5 %TPGDA 110.0(3.1) 453.3(1.6) 174.7(7.87) 38.3(2.03) 44.38(0.8) 615.5(11.6) 98.75(0.8) 

1 %TPGDA 121.0(9) 460.0(10) 170(8.6) 39.5(1.37) 43.36(0.3) 607.23(7.7) 97.05(1.5) 

2 %TPGDA 128.0(3) 723.0(9) 166.2(7.85) 48.8(1.01) 41.17(0.8) 556.94(8.5) 97.43(1.3) 

0.5 %HDDA 108.5(0.3) 442.2(2.9) 183.7(6.5) 38.0(1.21) 44.96(0.5) 610.25(4.9) 99.17(1.1) 

1 %HDDA 118.1(5.1) 725.4(8.3) 174.7(3.32) 48.1(0.54) 44.41(0.7) 604.5(12.7) 97.19(0.5) 

2 %HDDA 145.3(3.5) 856(4.4) 171.4(1.52) 56.4(1.14) 41.78(0.4) 571.48(9.7) 97.6(0.7) 

HDDA was expected to have higher mechanical strength compared to TPGDA due to its low molecular weight 

thus more compact blend occurred. Otherwise for TAIC, just 0.5 % addition has shown the increment in 

flexural strength and modulus. It figures that TAIC have alters samples properties becoming more resistance 

toward bending resistance. However, 1 and 2 % TAIC shows a reduction in tensile and flexural strength, 

elongation % and impact resistance. This might be due to the brittle behaviors reduce the ability of the sample 

to resist deformation with the load applied on it (Zainuddin et al., 1999). Impact strength was done to test the 

ability of every formulation to absorb applied energy. Increment of HDDA content showed that the HDDA 

imparts good molecular flexibility. With only 0.5 % loading, TAIC improved the modulus a lot but it also 

degrades impact properties. It illustrates that the increase in stiffness associated with decrease in impact 

strength. Besides, poor compatibility of TAIC particle during blending also lead to poor impact and others 

mechanical properties. HDDA and TPGDA are well dispersed in PBS allowing the blends to dissipate a 

significant amount of impact energy. Morphological observation indicates a finer dispersion of HDDA. From 

the Figures 1a, the particles are uniformly distributed in the PBS and do not give an indication of aggregation. 

Aggregates, such that the cracks will propagate easily and rapidly, causing premature failure. Table 1 shows 

the impact strength of the investigated samples. As the HDDA and TPGDA content increases, the impact 

802



strength increases. These was probably due to the sufficiently high amount of polymer radicals produced that 

react with monomers at these doses. The increased tensile strength with HDDA amount was due to the 

slightly increased crosslinking in the amorphous PBS region that resulted in the production of polymer radicals 

and hydrogen radicals (Liu et. al. 2017). HDT were also tested to detect the temperature of the blends 

deforms under a specified load. For 2 % TAIC, to high crosslinking decrease its elongation percent. But, the 

high crosslinking is very useful during high temperature applications where it can stand until 101.5 °C in hot oil 

environment. Therefore, high temperature needs to break the crosslink and thus make it bend (Piah et. al. 

2016).  Since the HDT result was very marginal, the increasing of cross linking did not affect the HDT result. 

3.3 Scanning electron microscopy 

Figures 1a to 1f on SEM images shows the sample degradation surface before and after 2 month the soil 

burial without oxygen. 

  
(a) (b) 

  
(c) (d) 

  

(e) (f) 

Figure 1: SEM micrograph of the samples before and after 2 months in natural soil burial (a) PBS/2 %TAIC 
before soil burial (b) PBS/2 %TPGDA before soil burial (c) PBS/2 % HDDA after soil burial (d) original PBS 
after soil burial (e) 2 % TAIC after soil burial (f) 2 % TPGDA after soil burial. 

803



Before the soil burial test, the pure PBS presented a relative smooth and clear surface. The images were take 

on the surfaces because microbial erosion is likely beginning from the surface of polymer. It seen that for all 

sample, degradation already occur even in 2-month burial time resulting from microbial attack. For all buried 

samples, it shows that the microorganism is well growth on the surface, the surface was considerably eroded 

and partial defect formed on the surface. Only a few areas of original and the degradation caused a very 

rough topography, creating a larger surface area due to microbial attack. It illustrates that even for high 

crosslinked density sample, it still can be digested by microorganisms and has equal degradation rate to 

uncross linked PBS. It can be concluded that PBS is stable in the atmosphere but biodegradable in soil with 

the molecule breakdown or broken chains in the networks start less than 2 months.  

4. Conclusion 

Radiation influences the properties of polymer materials. These results explained that low doses of radiation 

can promote crosslinking over degradation reactions to the PBS polymer. Suitable radiation dose of polymer 

materials was needed to improve properties of materials thus suit the industrial application. The optimum 

radiation dose which PBS can absorb is 20 kGy and intensive chain scission induced by irradiation at above 

20 kGy reduces the length of PBS macromolecules and thus cause a decrease in molecular weight, strength, 

and elongation at break. EB radiation above 20 kGy will just promote degradation and made the material 

brittle, hence higher dose for crosslink is not preferable. Addition of crosslinking agent influence the absorption 

efficiencies ability. Increasing addition of TAIC promotes brittleness due to its high reactiveness. 2 %TAIC 

shows marginal increment in HDT and 0.5 % TAIC depict the highest flexural strength and modulus. HDDA 

illustrate the highest toughness for properties like elongation, impact and tensile strength. Increasing the used 

of HDDA liquid make the sample become less stiff thus make it become more ductile. Overall in mechanical 

terms, HDDA and TPGDA produce less stiff properties but increase in toughness of the PBS. Overall, the 

used of electron beam radiation with the crosslinker agent have improved the PBS. The properties of PBS can 

be altered suitable with the applications and it will degrade when no oxygen occur hence reducing 

environmental problems caused by plastic waste. 

Acknowledgements 

We would like to express gratitude to Research Management Centre (RMC) and MOSTI for funding this 

project. The authors greatly thank all the staffs of the Polymer Plant, Radiation Processing and Technology 

Group for the helpful guidelines, facilities and experiment. The authors are grateful to Miss Zaiton for her 

assistance in obtaining SEM images. 

Reference 

Boye W.M., 2008. Utilizing coagents in the electron beam cure of elastomers. In Proceedings of the 57th 

International Wire & Cable Symposium, 2008, 335-341. 

Capek I., 1999. Radical polymerization of polyoxyethylene macromonomers in disperse systems. In Radical 

Polymerisation Polyelectrolytes (1-55). Springer, Berlin, Germany. 

Liu G.C., Zhang W.Q., Zhou,S.L., Wang X.L. Wang Y.Z., 2016. Improving crystallization and processability of 

PBS via slight cross-linking. RSC Advances, 6(73), 68942-68951. 

Piah M.R.M., Baharum, A., Abdullah, I., 2016, Mechanical properties of bio-composite natural rubber/high 

density polyethylene/mengkuang fiber (NR/HDPE/MK). Polymers and Polymer Composites, 24(9), 767. 

Ratnam C.T., Nasir M., Baharin A., Zaman K., 2000, Electron beam irradiation of epoxidized natural 

rubber. Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with 

Materials and Atoms, 171(4), 455-464. 

Riess G., Hurtrez G., Bahadur P., 1985. Encyclopedia of polymer science and engineering, Vol 2, 324, Wiley, 

New York, United States.  

Rytlewski P., Malinowski R., Moraczewski K. Żenkiewicz M., 2010. Influence of some crosslinking agents on 
thermal and mechanical properties of electron beam irradiated polylactide. Radiation Physics and 

Chemistry, 79(10), 1052-1057. 

Zainuddin, Razzak M.T, Yoshii F, Makuuchi K.,1999. Radiation effect on the mechanical stability and 

biodegradability of CP/Bionolle blend, Polymer Degradation and Stability, 63,311-320. 

 

804