Mechanical properties of gradient-modulus composite polyurethane isocyanurate polymeric materials

Transcription

1 Plasticheskie Massy, 9, 200, pp Mechanical properties of gradient-modulus composite polyurethane isocyanurate polymeric materials L. V. Luchkina, M. D. Petunova, A. A. Askadskii, V. V. Kazantseva, and O. V. Afonicheva A. N. Nesmeyanov Institute of Heteroorganic Compounds, Russian Academy of Sciences Selected from International Polymer Science and Technology, 33, 11, 200, reference PM 0/09/20; transl. serial no Translation submitted by P. Curtis By reaction forming, through reactions of polycyclotrimerisation and migration polymerisation, composite gradient-modulus polymeric materials are produced in which the elastic modulus and other properties change smoothly through the thickness, and here the materials possess elastic but not viscoelastic properties in the transition zone from the glassy to the rubbery state, which distinguishes them from well-known materials. Reactions of the production of polyurethane isocyanurate (PUIC) polymeric materials are described in detail in references [1] and [2]. In the present work the physicomechanical characteristics of obtained PUIC materials have been investigated, and the infl uence of the ratio of the polyisocyanurate (PIC) and polyurethane (PU) components on the properties has been assessed. The polymer binders used were crosslinked PUICs of controlled composition, based on polypropylene glycol (PPG) with a molecular weight of 2200, 2,4- toluylene diisocyanate (TDI), and diamine [di(3-chloro- 4-aminophenyl)methane]. The initial TDI concentration in its mixture with oligoester diisocyanate (OEC) in the synthesis of gradient-modulus materials was 50 and 0 wt.%. The polycyclotrimerisation catalyst was a complex catalyst based on dimethylbenzylamine and epoxy resin ED-22 in a 1:20 ratio [3, 4]. The reinforcing material was a fibrous carbon material based on cellulose hydrate fibres (carbon fabric of grade UVIS-T), and the support of the polymeric precursors was fl exible polyurethane foam (PUF) of grade PPU-EM-1 porolon, which hardly affected the properties of the gradient-modulus materials obtained. The formation of a three-dimensional structure and the forming of articles end at the compression moulding stage. By varying the temperature, pressure, and time, and also taking into account the technology for synthesising polyurethanes [5], the optimum compression moulding conditions were established, and s measuring mm were produced. Dynamic mechanical analysis (DMA) was carried out on a DMA-983 instrument (DuPont). Specimens were frozen to subzero temperatures, after which they were heated at a rate of 1 K/min; the tests were conducted at a frequency of 1 Hz. Specific impact strength and cross-breaking strength tests were conducted on a Dinstat instrument for gradient-modulus s on two sides. The testpiece was fastened cantilever-wise, and the hammer struck either the rigid side of the or the flexible side. The magnitude of abrasion of the rubber compounds was determined on an instrument of the Schopper Schlobach type. The method consists in determining the abrasion during sliding of a cylindrical over a drum rotating at constant speed with a surface coated with abrasive material, and with its simultaneous movement along the guide of the drum. The rebound resilience was determined on a pendulum elasticity meter according to the ratio of the energy regained by the rubber after being struck by the pendulum (hammer) to the total energy applied on impact. Brinell hardness tests were conducted on a TP-1 hardness meter by indenting a steel ball of 4.95 mm diameter at a constant deformation rate. Several measurements were carried out at different sites over the entire surface of s on the two sides Smithers Rapra Limited T/9

2 The elastic modulus was calculated on the basis of data from measuring the hardness and determined by means of the Hertz formula: 3 3F E = 1 h R 3/ 2 1/ 2 where h is the depth to which the spherical indicator penetrated (m), R is the radius of the indicator (m), and F is the force of indentation (N). IR spectra were measured on a Magna-750 IR Fourier spectrometer of the US company Nicolet with a spectral resolution of 2 cm 1 in the region cm 1. Specimens for spectral analysis were prepared in the form of KBr pellets. RESULTS AND DISCUSSION A spectral analysis was carried out on the gradientmodulus composite materials obtained, the composition of which varied through their thickness. One of the spectra of gradient-modulus reinforced polymeric material is presented in Figure 1. A computer search of the library of spectral data showed that the spectra of the obtained materials were similar to those of polyurethanes. However, they contain certain differences, most notably the presence of cm 1 and cm 1 bands []. These bands are characteristic of polyisocyanurates. Since IR spectroscopy established that there are four main types of bond characteristic of PU in the gradient-modulus polymeric materials formed, namely urethane bonds ( cm 1 ), urea bonds (1550 cm 1 ), and biuret and allophanate bonds (10, 1280, and 1310 cm 1 ), and also bands characteristic of polyisocyanurate rings, it can be asserted that, as a result of reaction forming, PIUC polymeric materials were obtained. Differences observed in a number of spectra (depending on the composition of the material) concern the intensity of the above bands. One of the most important parameters determining the nature of the mechanical behaviour of polymers (elastic or viscoelastic) is the mechanical loss tangent tg δ [7]. As is known, for elastic materials tg δ is very small, but, with viscoelastic behaviour, especially in the zone of transition from the glassy into the rubbery state, tg δ increases sharply. In this connection, a number of gradient-modulus composite PIUC materials with different ratios of the PIC and PU components were synthesised and investigated. By way of example, let us examine a gradient-modulus reinforced PUIC with a high PU content (80%) that smoothly passes into polyisocyanurate (PIC). In connection with this, the elastic modulus changes from a medium value (980 MPa) characteristic of the glass-to-rubber transition zone to a considerable magnitude (100 MPa) characteristic of a glassy polymer. For the, DMA was conducted with determination of the temperature dependences of the modulus of accumulation Gʹ, the modulus of losses Gʹʹ, and the mechanical loss tangent tg δ = Gʹʹ/Gʹ (Figure 2). This last quantity characterises the absorption of mechanical energy under vibrations. The conducted TMA showed that there is a small and smooth reduction in the elastic modulus, the retaining increased values up to 200 C, while tg δ for the networks obtained by us is very low (less than 0.1) in a wide temperature range, in spite of a modulus of Figure 1. IR spectrum of gradient-modulus reinforced polyurethane isocyanurate polymeric material. Composition of material: rigid side PIC; flexible side PIC/PU = 0:40; TDI concentration in its mixture with OEC in PIC composite amounted to 0 wt.% T/10 International Polymer Science and Technology, Vol. 34, 9, 2007

3 Figure 2. Temperature dependence of mechanical loss tangent tg δ for polyurethane isocyanurate gradient-modulus reinforced polymeric material. Composition of : rigid side PIC; fl exible side PIC/PU = 50:50 and 20:80; TDI concentration in its mixture with OEC was 0 wt.% accumulation value characteristic of the transition zone. In this property, the materials obtained in the present work basically differ from known polymers; the behaviour of the obtained gradient-modulus PUIC materials is elastic. Here, the durability of the materials is retained up to 200 C. Such a result is entirely consistent with the concept put forward earlier in the laboratory of polymeric materials of the Institute of Heteroorganic Compounds concerning the fact that, for such mechanical behaviour, it is necessary for a polymer network to be formed that contains bulky crosslinked points and short chains connecting these crosslinks [7]. Thus, for the production of vibration-absorbing materials, it is possible to use gradient-modulus reinforced materials in the form of sheets in which the PU smoothly passes into PIC. For gradient-modulus composite PUIC polymeric materials, the following data on the physicomechanical properties, which are presented in Table 1, were obtained. Porolon (h = 10 mm) was used as the support of polymer composites. The properties of the obtained materials changed through the thickness of the article (h = mm). It can be seen that there is a slightly higher specific impact strength when the flexible side of the material is struck by the hammer by comparison with striking of the rigid side containing only the PIC component. The greatest values are characteristic of s in which the TDI concentration in its mixture with OEC in PIC composites amounts to 0 wt.% (Table 1, s 14 19, impact tests on the flexible side of the material). It was established that, with increase in the PU component in gradient-modulus s with a PIC/PU ratio of 50:50 and 40:0, this quantity acquires a maximum value of 1.9 and 13.7 kg cm/cm 2 respectively (s 17 and 18). A comparative analysis of the values of the specific impact strength for s tested on both sides for each PIC/PU ratio showed that this index remains practically identical and only in some cases is twice as high (s 12 and 24). The cross-breaking strength acquires its highest values in the case of bending of the flexible side of the material, and these values are higher the greater the proportion of PU component in the polymer composite ( 21). In connection with the fact that the values of the specific impact strength were low for gradientmodulus composite materials, an attempt was made to produce high-impact materials with increased values of the specific impact strength by means of reinforcement with reinforcing fillers. Carbon fibrous material carbon fabric of grade UVIS-T was chosen as such a filler. For reinforced gradient-modulus polymeric materials, the change in the physicomechanical properties with different ratios of PIC and PU is presented in Table 2. As was to be expected, the highest specific impact strength and cross-breaking strength are characteristic of polymers for which impact strength and crossbreaking strength tests were conducted on the flexible side of materials containing different amounts of the PU component. For s impact tested on the rigid side, the indices of the specific impact strength were practically identical and ranged from 11 to 17 kg cm/cm 2. At the same time, the cross-breaking strength acquired high values with increase in the PU component on the flexible side of the, thereby having an influence of the values on the rigid side. It was established that the specific impact strength readings for s impact tested on the flexible side are affected by the quantitative content of the PU component. In these s the isocyanurate crosslinked points are separated by flexible PU fragments containing polypropylene oxide groups. Thus, the greater the PU content in relation to PIC, and consequently to TDI in the initial composite, the higher are the values of the specific impact strength, or the material does not undergo failure at all and only bends in tests on the Dinstat instrument. However, properties such as cross-breaking strength and elastic modulus have minimum values. Table 3 presents the characteristics of gradientmodulus reinforced polymeric materials for which the Brinell hardness and the elastic modulus change through the thickness of the ( mm). To produce such s, use was made of 5 layers of reinforced material. Three layers were impregnated with PIC composite and 2 3 layers were impregnated with a composite with different PIC/PU ratios. The TDI content in its mixture with OEC in the PIC composite amounted to 50 and 0 wt.%. For s 2 7 the TDI concentration amounted to 0 wt.%, and for s 1 and 8 12 it amounted to 50 wt.%. For the materials presented (Table 3) the elastic modulus changes considerably from one surface of the material (rubbery) to the other (glassy). When the indentor penetrates into the rubbery (flexible) surface, with increase in the depth of indentation the elastic modulus 2007 Smithers Rapra Limited T/11

4 Table 1. Physicomechanical properties of gradient-modulus polyurethane isocyanurate polymeric materials produced by reaction forming. Support of precursor porolon Concentration of TDI on rigid side of PIC/PU ratio on flexible side of Degree of filling, g p /g f Specific impact strength, kg cm/cm 2 Cross-breaking strength, kg /cm 2 Impact strength and cross-breaking strength tests conducted on rigid side of gradient-modulus s 1 50 PU PU : : : : : : : : : : Impact strength and cross-breaking strength tests conducted on flexible side of gradient-modulus s PU PU : : : : : : : : : : increases, whereas, when the indentor penetrates into the glassy (rigid) part of the surface, as the indentor penetrates into the material the elastic modulus decreases. Thus, measurement of hardness occurs not on the surface itself but at a certain depth prescribed by the load. It was established that, with increase in the PU component, in the flexible part of the material the depth of entry of the indicator into the testpiece increases, and consequently the hardness and elastic modulus values decrease. The elastic modulus changes from 98 MPa (s 3 7) to 89 MPa ( 2) and from 820 MPa (s 8 12) to 54 MPa ( 1). This is characteristic of s whose flexible part (s 1 and 2) contains only PU. On the rigid side, which contains only PIC, these indices acquire their highest values, and the indices increase with decreasing PU on the fl exible side of the. Consequently, the flexible side will contain more PIC and, as a consequence, the TDI concentration will be greater (s 3, 4, 8, and 9). On the other hand, with increase in the PIC component in the flexible part of the, and consequently with increase in the TDI concentration in the PIC, the hardness and elastic modulus values on the rigid side increase to values characteristic of materials lying in the transition zone from the rubbery into the glassy state, and in some cases their elastic modulus values approach those of glassy polymers (s 3 10 and 12). The elastic modulus and hardness values of the materials are also affected by the initial TDI concentration in the mixture with OEC. At a TDI concentration of 0 wt.%, the values of these properties are higher. In a comparative analysis, this can be clearly seen in s 2 7, 8 12, 1, and 2. Specimens 1 and 2, consisting only of PIC on one side of the material and of PU on the other side, with different TDI contents, have the lowest values T/12 International Polymer Science and Technology, Vol. 34, 9, 2007

5 Table 2. Physicomechanical properties of gradient-modulus polyurethane isocyanurate polymeric materials produced by reaction forming. Reinforcing material UVIS-T Concentration of TDI on rigid side of PIC/PU ratio on flexible side of Specific impact strength, kg cm/cm 2 Cross-breaking strength, kg /cm 2 Impact strength tests and cross-breaking strength tests carried out on rigid side of gradient-modulus s 1 50 PU PU : : : : : : : : : : Impact strength tests and cross-breaking strength tests carried out on flexible side of gradient-modulus s 1 50 PU PU : : : : : : : : : : of hardness and elastic modulus, which is connected with penetration of one layer of the composite into another during compression moulding. For material containing 0 wt.% TDI these values are a little higher than for material containing 50 wt.% TDI (s 1 and 2). It is also necessary to point out that the values of the elastic modulus and hardness are affected by the compression moulding conditions of the materials obtained. It was established that, with increase in the compression moulding temperature (to 200 C) of material containing PIC/PU = 80:20, the elastic modulus in the rigid part decreases almost by 400 MPa by comparison with 3 moulded at 150 C. This may be connected with degradative processes occurring in the polyurethane isocyanurate at 200 C. It is known that degradation in PU begins at only 10 C, and 3a contains 20% PU in relation to PIC, which explains the reduction in elastic modulus. We also estimated the magnitude of abrasion of gradient-modulus composite and reinforced polymeric materials on a Schopper Schloban instrument (Table 4). Specimens 1 7, presented in Table 4, contain porolon as a support for the polymer composite, while 8 contains a filler (carbon fabric UVIS-T). Specimen 5 contains 2 wt.% carbon black of grade K354, and contains 2 wt.% of carbon black P803. The carbon grades differ in activity, dispersity index, and degree of structure, which affects the evenness of colouring, the elastic modulus, the hardness, and the magnitude of abrasion of the materials obtained [8]. It was established that abrasion has the lowest values on the side of the gradient-modulus that contains only PU or a greater content of PU in relation to the PIC component. In this case the abrasion has values characteristic of standard rubber compounds and varies in the range cm 3 /m. With increase in the 2007 Smithers Rapra Limited T/13

6 Table 3. Characteristics of through-thickness gradient-modulus polyurethane isocyanurate polymeric materials produced by reaction forming. Filler UVIS-T Concentration of TDI on rigid side Composition of reinforced rigid side flexible side PIC/PU Degree of filling of rigid/ flexible sides 1 50 PIC PU 1.41/ PIC PU 1.15/1.87 Brinell hardness HB of sides, kg/mm 2 Elastic modulus E, MPa flexible rigid flexible rigid PIC 80: / a 0 PIC 80: / PIC 0: / PIC 50: /2.2 0 PIC 40:0 1.15/ PIC 20: / PIC 80: / PIC 0: / PIC 50: / PIC 40:0 1.41/ PIC 20: / Filler UVIS-T- 22R number of layers 5 T/14 International Polymer Science and Technology, Vol. 34, 9, 2007

7 Table 4. Characteristics of abrasion for gradient-modulus polymeric materials Concentration of TDI in PIC Composition of sides of PIC/PU m av, g m f, g p, g/cm 3 side I 10 3, cm 3 /m Abrasion index of flexible rigid flexible rigid flexible rigid 1 50 PU 80: PU 0: PU 20: PU PIC PU 80:20 K PU 80:20 P :50 0: :80 PIC concentration of the PIC component on the rigid side of the material, the abrasion increases to significant values ( cm 3 /m). It was noted that the magnitude of abrasion is also affected by the grade of carbon black. With the use of P803 (a finely dispersed powder), the abrasion is lower than when K354 is used (s 5 and ). For gradient-modulus reinforced material the following pattern is observed: abrasion has its highest values for the rigid side consisting only of the PIC component. However, the values of abrasion of reinforced materials are higher than those of composite materials where porolon was chosen as the support of the polymeric precursors. With increase in the PU component in the material, abrasion has its lowest values, only slightly higher than the abrasion values characteristic of standard rubber compounds. This indicates that, when a PU component is introduced into Table 5. Characteristics of single-modulus and gradient-modulus composite materials produced by reaction forming. Support porolon (h = 2 cm) TDI concentration in its mixture with OEC in PIC composite Composition of flexible side Composition of rigid side Rebound resilience of flexible/ rigid side, % Shore A hardness 1 50 PU 80:20 40/ / PU 0:40 40/3 8/ PU 20: /38 9/ PU PIC 41/38 73/98 5 0, 2% K354 PU 80: / /94 0, 2% P803 PU 80:20 38/43 8/ :50 0:40 42/40 95/ :0 40: PU 1025 PU PU V-13 PU V :80 90: /44 81/ :40 80:20 34/3.3 90/ :0 50:50 40./ / PU 40:0 33.7/3.7 81/ :50 80:20 34/38 82/ :80 0:40 33/34 70/95 Note. V-13 is a sealant based on oxypropylene (molecular weight 1000) and polyisocyanate (crude MDI) 2007 Smithers Rapra Limited T/15

8 Table. Characteristics of gradient-modulus composite materials produced by reaction forming. Support porolon (h = 1 cm) TDI concentration in its mixture with OEC in PIC composite PIC/PU ratio on flexible side Composition of rigid side Rebound resilience of flexible/ rigid side, % Shore A hardness 1 50 PU PIC 31.7/ / PU PIC 34/ / :20 PIC 59.3/ / :40 PIC 55.3/ / :50 PIC 4.3/ / :0 PIC 40/48 95/ :80 PIC 35.7/50 91/ :20 PIC 48/57 93/ :40 PIC 48/ / :50 PIC 41/54 94/ :0 PIC 40/51 93/ :80 PIC 3.3/ / :80 PIC 44/4 85/97 Note: s 1 12 contain porolon support, and 13 contains carbon fabric UVIS-T polyisocyanurate materials, the wear resistance of the materials obtained increases. For some gradient-modulus polymeric materials, the Shore A hardness was determined and the rebound resilience was measured using a pendulum elasticity meter developed by Schob and Van Intersen (Tables 5 and ) [9]. It is clear that the rebound resilience is higher in the flexible part of materials containing either PU or a greater amount of PU in relation to PIC (Table 5, s 1 5). The hardness is always higher in the rigid part of the material containing a greater amount of the PIC component, and consequently a greater amount of TDI. For gradient-modulus materials, one side of which always consisted of PIC while the other contained a different PIC/PU ratio, the rebound resilience and hardness were always higher for the rigid part of the material (Table ). The rebound resiliences for gradient-modulus reinforced polymeric material with rigid and fl exible sides are practically identical and have values of 4 and 44% respectively. Note that the Shore A hardness for gradient-modulus material is fairly high and amounts to 85 nominal units for the flexible part and to 97 nominal units for the rigid part (Table, 13). Thus, as a result of reaction forming by reactions of polycyclotrimerisation and migration polymerisation, gradient-modulus polymer composites have been obtained in which the elastic modulus and other properties change smoothly through the thickness of the material, and here the materials possess elastic rather than viscoelastic properties in the transition zone from the glassy into the rubbery state. The effect of PIC and PU components on the physicomechanical properties of gradient-modulus PUIC materials has been assessed. REFERENCES 1. A. A. Askadskii et al., Electronic journal Issledovano v Rossii, 9, 2004, pp articles/2004/09.pdf. 2. L. V. Luchkina et al., Zhurnal Prikladnoi Khimii, 78, 8, 2005, p A. A. Askadskii et al., Vys. Soed., A32, 7, 1990, p A. A. Askadskii et al., Vys. Soed., A37, 5, 1995, p Yu. S. Lipatov et al., Structure and properties of polyurethanes. Naukova Dumka, Kiev, L. Bellamy, Infrared spectra of complex molecules. Izd-vo Inostr. Lit., Moscow, A. Ya. Malkin et al., Methods for measuring mechanical properties of polymers. Khimiya, Moscow, State standard. Carbon black for rubber production. GOST Official publication. E. 9. M. M. Reznikovskii and A. I. Lukomskaya, Mechanical tests of rubbers. Khimiya, Moscow, 198. (No date given) T/1 International Polymer Science and Technology, Vol. 34, 9, 2007