COMPARATIVE STUDY OF EB AND UV CURED POLYMER FILMS

Transcription

1 COMPARATIVE STUDY OF EB AND UV CURED POLYMER FILMS M. Azam Ali, F. Akhtar and K. M. Idriss Ali Bangladesh Atomic Energy Commission P.O. Box 3787, Dhaka-1000, Bangladesh Fax: ; MYOOo'i i' I ABSTRACT A number of formulations were developed with urethane diacrylate oligomers in combination with several reactive diluent monomers of different functionalities in the presence of certain co-diluent co-monomers. Thin polymer films were prepared with these formulated solutions using either electron beam (EB) or ultraviolet (UV) radiation. Physical, mechanical and thermal properties of the radiation cured films were studied and correlated with the glass transition temperature (Tg) of the homopolymer of diluents and codiluents. Tensile properties (strength and elongation) were almost double with the UV-cured films than those of the EB-cured films of the similar formulation. Thermal behavior was also found to be different in these two systems. The co-monomers played significant role to produce more shape recovery films than the oligomer/diluent system. The co-diluents also induced shape recovery character in the film whose Tg values are lower than 0 C. This is unique. II INTRODUCTION Polymer is a versatile and wonder material used for diverse applications and purposes starting from aero-space to kitchen spoon, nuclear submarine and warheads to shopping bags. Some polymers are soft and flexible while others are tough and rigid. The diverse characteristics are possible for polymers, only because the polymers are generally prepared with certain formulations composed of oligomers, reactive monomers, co-monomers and additives. Each of the starting materials has specific functions to play during the polymerization. Different functional groups and backbone structure present with the individual ingredient play significant role on the overall properties of the polymer formed. It is universally known that physical properties such as tensile, thermal, mechanical, etc. are dependent on the structural and geometrical shapes of the molecules and these are in turn, related with their glass transition temperature, Tg (1-4). In the present investigation, polymers are made under EB and UV radiation using formulations of different natures involving oligomers, monomers and co-monomers; attempt is made to correlate their physical and mechanical properties with the Tg values of the constituents in order to compare the properties of the EB-cured polymers to those of the UV-cured ones. 4

2 Ill EXPERIMENTAL Urethane diacrylate having aliphatic or aromatic backbone chain with two acrylate groups at two ends of the molecule, reactive monomers and co-monomers of different functionalities and photoinitiator were procured from the respective suppliers. Some of their physical properties and Tg values are given in Table 1. The Tg values are taken from literature (5). Table 1 Some physical properties of co-monomers, monomers and oligomers Name Co-monomer Ethyl acrylate Methyl acrylate Cyclohexyl acrylate Vinyl acetate t-butyl acrylate Monofunctional monomers 2-Methoxy ethyl acrylate 2-Hydroxy ethyl acrylate 2-(2-0x0-3-oxazolidinyl-etyl acrylate N-Butyl carbamate ethyl acrylate Diclopentanyl acrylate N-Vinyl pyrrolidone Multifunctional monomers Tripropylene glycol diacrylate Trimethylol propane triacrylate Oligomers Urethane diacrylate (aliphatic) Urethane diacrylate (aromatic) Abbreviation Vac M H CL,959 CL1039 DPA NVP TPGDA TMPTA M0 Ml 100 Mot. Wt Tg() Formulated solutions were prepared as oligomer:monomer:co-monomer = 50:25:25:w/w for EB system and oligomer:monomer:co-monomer:photoinitiator = 50::.2, w/w for UV system. Polymer films were prepared under radiation on the glass plate coated with the formulated solutions using a bar coater (No.0.018) of Abbey Chemicals Co. (Australia). A Minicure UV machine of lst-technik (Germany) was used for the UV radiation applying 2 kw dose per pass (1 m/min) under a lamp ( run). An electron beam (EB) accelerator machine called Curetor of Nissin- High voltage Co. (Japan) was used for the EB radiation. The accelerating voltage was 0 kev at 15 ma current and the conveyor speed was 75 m/min. Polymer films were then characterized to determine their tensile properties and thermal characters. Tensile properties, particularly strength (TS) and elongation at break (Eb) were directly measured with INSTRON (model 1011) using cross head speed 3 cm/min with load capacity of 2 kg and gauge length 1.2 cm. Polymer films were folded at 1 using a pressure of 2 kg/cm 2 at 25 C; the deformation persisted overnight with some films and this could be removed by heating at certain temperature above 25 C for lh. This temperature is called the shape recovery temperature (SRT). 5

3 IV RESULTS AND DISCUSSION Tensile properties Results of tensile properties (strength TS and elongation at break Eb) of the radiation cured polymer films of urethane acrylate/monomers/co-monomers are shown in Table 2. The glass transition temperature values of cured films Tg(CF) were calculated on the basis of the Fox equation (6). Among all the monomers used for the preparation of these polymer films, NVP induced the highest strength (TS) to the polymers in the presence of the co-monomer with both EB and UV system; however, the TS values of polymers are much higher for the UV process than the EB one. The monomer DPA has produced the second highest tensile strength in these two systems. NVP has produced the films of the highest TS values, because NVP has the ability of better augmentation with the neighbouring groups and constituents through - N = CO- group present in NVP (7). The monomer NVP has also played similar role to enhance TS values in other systems also (8-9). The lowest TS values of the UV system are obtained with CL1039 series, whereas films of M and H series have produced the lowest TS values in the EB system. The above results illustrate a significant importance between UV and EB systems. The soft radiation of UV rays used for the preparation of polymers plays important role to allow different constituent ingredients to properly align their geometry in line of obtaining a matrix for inducing the maximum strength to the polymer films at the equilibrium condition during the polymerization process. The high energy radiation of EB has possibly disturbed this process to some extent, thereby reducing the overall tensile strength of the polymers. Polymer films of both UV and EB systems have attained the maximum TS values, mostly in the presence of with M, DPA and NVP series and the minimum TS values with CL959, CL1039 and H. The reasons of this phenomenon are yet to be explored; but it is very likely that this contrasting behaviour may relate to the different structural shape and geometry of the reacting ingredients of both monomers and co-monomers used in the formulation. Polymer films prepared with UV radiation have not only obtained higher TS values than those of the EB system, these films have also higher elastic property denoted by Eb values. Most of the monomer series like M, H, CL959 and CL1039 have higher Eb values with the UV system compared to Eb values obtained with EB system. However, NVP and DPA series have shown slightly higher Eb values with EB system than the UV process. The highest TS values obtained with NVP and DPA may indicate that there is higher crosslinking phenomena in these systems; the high density of crosslinking has probably reduced elastic nature of the polymer indicating lower Eb values with NVP and DPA series. The differential behaviour of the UV-cured and EB-cured polymer films of similar formulations is undoubtedly important for diverse applications of these polymers. 6

4 Monomer Table Tensile and thermal properties of the polymers films Co-monomer Cured films UV system EB system Tg(CF) TS Kg/m 2 Eb % SRT TS Kg/m Eb % SRT M Tg=ll H Tg=15 CL959 Tg= CL1039 Tg=1.6 DPA Tg= Vac NVP Tg= Thermal property: Polymer is such a unique material that it is used in diverse applications under different weathering conditions. Among all other thermal properties, the shape recovery property of the radiation cured polymers has been studied in this particular investigation. Many of the polymer films prepared with urethane diacrylate oligomer have been found to possess such shape recovery character. The results of shape 7

5 recovery temperatures (SRT) of different polymers obtained with EB and UV system are presented in Table 2. All the UV-cured polymer films require heating above the ambient temperature (25) in order to regain the original shape from the deformed condition; but there are some polymers of EB radiation system which need heating below for regaining from the deformed shape. Polymers of NVP and DPA have higher shape recovery temperature in the EB system compared to the UV-system. The shape recovery temperature (SRT) is initially higher with co-monomers of low Tg values and then decreases up to Tg values of homopolymers of and then rises again. The behaviour is different with UV system. V CONCLUSION The data presented in Table 2 are typical results of tensile and thermal properties of polymers of urethane diacrylate prepolymer combined with other monofunctional monomers and co-monomers. The results reveal that the UV-cured polymers possess higher TS and Eb values than the corresponding EB-cured polymers prepared with similar formulations. The UV-cured polymer films also contain uniform order in the determination of their various properties. The shape recovery temperatures of the UVcured polymer films are more defined than that of the EB-cured polymers. It can therefore, be concluded that the UV curing is much more beneficial in some cases; the cost of UV processing is also much less than that of the EB system. To adopt and use UV processing technology is much easier and convenient than EB technology. VI REFERENCE 1. M. Azam Ali, M. A. Khan and K. M. Idriss AH; Polym, Tech. & Eng., (4), 5-37, K. M. Idriss Ali and T. Sasaki; Phys. Chem., 43(4), , M. Azam Ali, M. A. Khan and K. M. Idriss Ali; Adv. Polym. Technol., 17(1), 1, M. Azam Ali, M. A. Khan and K. M. Idriss Ali; Polym. Tech. & Eng., 37(2), 175, J. Brandrup and E. H. Immergut, Ed. Polymer Handbooks, 3 rd ed., Wiley New York, T. G. Fox; Bull. Am. Chem. Phys. Soc., 1, 1, K. M. Idriss Ali, M. A. Khan and M. M. Hussain; Radiat. Phys. Chem., 44(4), , K. M. Idriss Ali, M. A. Khan and M. M. Hussain; Polym-Plast. Technol. Eng., 32(4), 5-, M. A. Khan, M. N. Islam and K. M. Idriss Ali; Radiat. Phys. Chem., 48(3), ,