Novel Elastomers Based on Urethane alky...
Submitter: Eid Abd Allah Ismail
Novel Elastomers Based on Urethane alkyd / Poly (methyl acrylate) Semi- and Full Interpenetrating Polymer Network
Eid A. Ismail*, A. M. Motawie and A. M. Hassan; Petrochemicals Dept., Egyptian Petroleum Research Inst., Nasr City, Cairo, Egypt
Novel two-component semi- and full interpenetrating polymer networks (IPN) of urethane – soya alkyd resins (UA) and poly (methyl acrylate) (PMA) by sequential technique were studied. With and without using ethylene glycol dimethacrylate to form full and semi interpenetrating polymer network respectively. The elastomers obtained were found to be tough films and characterized by mechanical properties: such as tensile strength, elongation and hardness (Shore A). The apparent densities and thermal properties of prepared samples were determined and compared.
Keywords: - density, polyurethanes, strength, swelling, interpenetrating network (IPN), hardness, uralkyd, poly (methyl acrylate), TDI, tensile strength, polymer network.
Interpenetrating polymer network (IPN) are among the important class of polymers that it have unique properties in many industrial technology. During the last two decades, IPN technology has made enormous strides in the industrial applications. The concrete research is being done and their potential applications cover areas not easily covered by other possibilities.
* Correspondence author, e-mail: email@example.com
IPNs is a combination of at least two polymers both in network form and one of which is
Synthesized and cross-linked in the presence of the other . Some studies were carried out on oil based polyurethanes and their simultaneous interpenetration with vinyl monomers [2-8].
There are little reports available for IPNs based on uralkyd [9, 10]. Uralkyds are alkyd resins modified by did or polyisocyanates to obtain urethane alkyd with superior properties. They can be dissolved in hydrocarbon solvents to make coatings, which cure, by air oxidation of the unsaturated groups in the presence of metallic driers. Normal plastics such as polystyrene and poly methyl methacrylates are brittle; they can be improved by incorporation of elastomeric materials. Uralkyds are elastomers that can be used to improve the drawback of such plastics.
In our work, novel IPN elastomers based on uralkyd / poly methyl acrylate were synthesized and characterized.
Soya bean oil obtained from Cairo Co. for Oils & Soaps, having the properties listed in table 1. Toluene diisocyanate (TDI) was obtained from Bayer A.G. Pentaerythritol, phthalic anhydride, benzoyl peroxide, ethylene glycol dimethacrylate and methyl acrylate were obtained from Sigma.
Preparation of transesterified Soya bean oil polyol by pentaerithritol
1equiv. soya bean oil and 2equiv. pentaerythritol were stirred together at 180oC for 4h using 0.01% lead monoxide as catalyst in a three-necked flask fitted with mechanical stirrer, reflux condenser, and thermometer.
The experiment was carried out till soya bean polyol was formed. It was tested by the solubility of one part of polyol in three parts of methanol.
The properties of transesterified soya bean oil are shown in Table 1.
Preparation of hydroxyl terminated alkyd resins [8,9].
In the previous apparatus, the prepared polyol with 1equiv. phthalic anhydride were charged. The temperature was raised slowly to 210oC with continuous stirring, till pH of the mixture reach blow 5. Some xylene was used to remove water of the reaction by azeotropic distillation under vacuum using Dean & Stark tube.
Synthesis of Uralkyd Network
In a four-necked flask equipped with mechanical stirrer, thermometer and reflux condenser, 1equivalents of 50% solution in toluene of soya bean oil alkyd resin was charged. 2equivalents of TDI were dropped gradually through dropping funnel in a period of 1/2h with continuous stirring for 3h, Triethanolamine (0.1% by weight) was added and mixed for 5minutes. The resulting mixture was poured into a glass mold using silicon-releasing agent for one week before testing.
Formation of IPN
The apparatus consist of three-necked flask; equipped with mechanical stirrer, reflux condenser and thermometer. IPN were prepared by using different proportions of UA and methyl acrylate with 0.01% benzoyl peroxide as initiator. The constituents were mixed thoroughly for 20 minutes at 55oC, and then the temperature was raised to 80oC with continuous stirring for 2h to form semi interpenetrating polymer network. The experiment was repeated using ethylene glycol dimethacrylate to form full interpenetrating network. The resulting mixture was then poured into glass mold using silicon oil releasing agent.
Infra red spectra (IR) were carried out using Shimadzu FTIR spectrophotometer for IPNs and homopolymers. Tensile strength and elongation were carried out according to ASTM D 638 and hardness according to ASTM D 2240-75. Density was obtained by measuring the displacement volume of a known weight . Chemical resistance study was performed According to ASTM D 543-67 procedure. Thermo gravimetric analysis was carried out using Mettler TA at a heat rate of 10 oC.
Results and Discussions
Infra red spectroscopy
IR spectra of hydroxyl-terminated alkyd, isocyanate terminated-uralkyd, UA/PMA, IPN3 are shown in fig.1, 2,3 respectively. These figures show a characteristic absorption band in the range of C=O group at 1724 cm-1 in fig. 1,2 and 1726 cm-1 in fig. 3 respectively. NCO group appears clearly at 2264 cm-1 in fig.2. While, OH and NH groups appear in the range of 3422-3479 cm-1 in all figs.
The results of tensile strength, elongation and hardness are presented in Table 2. Tensile strength decrease and elongation increase with increasing percentage of uralkyd.
Tensile strength increase while elongation decrease with increasing isocyanate ratio
The tensile strengths of both the semi- and full-IPNs showing comparable values with the increase in PMA contents in the IPNs. All the semi-IPNs show higher elongation % compared to the full-IPNs. This can be explained by the fact that in the semi-IPNs, the constituent polymer (PMA) is maintained linear, so higher mobility than in the case of full-IPNs, because the high degree of cross-linking restricts the mobility of PMA chains.
It was observed also the hardness (Shore A) increased as the proportion of PMA increased because PMA is hard substitute the soft and flexible uralkyd resin. There was no noticeable change in the hardness of both the semi- and full-IPNs. PMA is characterized by highest tensile strength and lowest elongation as compared to the UA network. It was observed that the full-IPNs exhibited lower tensile strength and elongation than the corresponding semi-IPNs. This can be explained by considering the fact that the soft elastomeric UA moieties have much higher free volume, so greater mobility of UA than PMA network
Swelling study  was carried out by calculating the percentages of swelling for each IPN:
Swelling (%) =
(Weight of swollen polymer) – (weight of dry polymer) x 100
(Weight of dry polymer)
The swelling data of the IPNs in chloroform, toluene, MEK and water are reported in Table 4. It is obvious from the table that the swelling was more prominent in chloroform, toluene, MEK whereas no swelling was observed in water. Moreover the swelling values decrease in the direction: chloroform > toluene > MEK for both full- and semi-IPNs.
It was observed also that, the semi-IPNs exhibited greater swelling as compared to the full-IPNs. In the semi-IPNs the degree of cross linking is low as compared to full-IPNs, also the constituent polymers is linear and this enables the solvent to penetrate into the core of the IPN matrix easily, so increasing swellability.
The calculated densities were obtained by the equation:
d = w1d2 + w2d2 , where d is the density of the IPN sample, w1 and w2 are the weight fractions of the constituents, d1 and d2 are the corresponding densities.
It was found that the density of the UA homopolymer is higher than that of the PMA, so as the proportion of the UA-homopolymer increased in the blend, the density values were also found to increase correspondingly. Therefore, more and more PMA was being substituted by denser UA resin.
From Fig 3, the full-IPNs exhibit higher density values than their corresponding semi-IPNs.
The calculated density values of both full and semi IPNs lay over that of the experimental values. Further, the semi-IPNs, exhibited higher density values than their corresponding full IPNs. This was explained by the fact that, some “holes” in the amorphous uralkyd structure were filled by the self-entanglement of the growing network .
The thermal stability of the IPNs falls intermediate between those of PMA and urethane alkyd homoploymer. There is no significant difference in the degradation of semi- and full- IPNs There was no considerable difference in the degradation behavior of both the full and semi-IPNs. UA exhibited thermal degradation in the regions from 200-390oC, 390-450 oC, 450-540 oC. PMA showed single stage degradation in the region280-450 oC.
Several pieces of IPNs 20 x 20 x 0.78 mm were prepared and immersed into certain chemical reagents for 7 days: 25% H2SO4, 15% HCl, 5% HNO3, 5% NaOH, 10% NH4OH, 25% acetic, 5% H2O2, 40% NaCl, methyl ethyl ketone, toluene, CCl4, water.
Each of the IPN pieces was examined on the basis of physical appearance such as discoloration, loss of gloss, change in weight, and change in thickness. All samples were stable in all of these reagents except for methyl ethyl ketone, toluene and CCl4, which show increase in weight and in thickness.
The significant factors in IPN swelling are the NCO and MA contents. The swelling percentages decrease with increasing both NCO and MA contents, since the PU cross-links increase which cause hindering of the solvent entrance.
An investigation was made on the properties of full and semi IPNs based on urethane modified alkyd and polymethyl acrylate showed that enhancement of compatibility of UA and PMA to produce new elastomers having required properties.
Commercial applications will be produced because elastomeric uralkyd and plastic PMA gave synergistic results.
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Table 1 Properties of Soya bean Oil and modified -soya bean oil- by pentaerethritol
Oil Acid value, mg KOH/g Hydroxyl value, mg KOH/g Unsaturation, % Iodine value Saponific-
-ation value Viscosity, cps, 25oC
Soya bean oil 0.4 - 85 128 190 325
Transesterified oil by pentaerithritol 2.1 315 - - - 515
Table 2 Properties of full and semi- interpenetrating polymer network
Sample Composition of UA/MA
(wt.%) Tensile strength, kg/cm2 Elongation at break,
% Hardness, Shore A
Table 3 Swelling properties of IPNs
Sample Composition of UA/MA (wt.%) Chloroform Toluene MEK Water
Table 4 Thermal properties of homopolymers and of IPNs
Sample Composition of UA/MA (wt.%) 300oC 350oC 400oC 450oC