Investigation of the structural and strength characteristics of modified polycarbonate

Transcription

1 Plasticheskie Massy, No. 3-4, 2014, pp. 3 6 Investigation of the structural and characteristics of modified polycarbonate V.A. Zapornikov, V.S. Osipchik, A.A. Red kina, D.B. Zakharov, M.V. Mishurova, and T.P. Kravchenko D.I. Mendeleev Russian Chemico-Technological University Selected from International Polymer Science and Technology, 41, No. 11, 2014, reference PM 14/3-4/03; transl. serial no Translated by P. Curtis Summary Atom force microscopy was used to study the supermolecular structures of polycarbonate-based composites. The effect of modifiers on the formed supermolecular structures was investigated, and the dependence of the properties of the composites on their structure was established. INTRODUCTION Investigation of the supermolecular structure and the possibility of controlling the processes of formation of these structures is of interest not only from the viewpoint of polymer materials science but also from the viewpoint of applying polymeric materials in different areas of engineering, and also giving them a combination of necessary properties. Polycarbonate is one of the most promising thermoplastics owing to its unique combination of characteristics: high physicochemical, optical, and dielectric properties. The worldwide production of polycarbonate exceeds 3.2 million t and is increasing every year [1]. In Russia, according to Rosstat data, in the period from January 2012 to January 2013, polycarbonate production increased by 8.5% and amounted to t [2]. However, in a number of cases the application of polycarbonate is limited by its low cracking resistance, low resistance to UV radiation, and difficulty in processing. Polymer composites with a high specific surface are produced by using hollow microspheres, and these materials have been called spheroplastics [3 5]. In this work, home-produced hollow glass microspheres (HGMSs) were used. Foreign firms also produce HGMSs: Mineralien-Werke and Ilmenau in Germany, DuPont in the United States, and Toshiba, Fuji, and Garasu K.K. in Japan. Russian grades of glass hollow microspheres are practically on a par with foreign hollow microspheres; their comparative properties have been given fairly comprehensively by Simonov-Emel yanov et al. [4]. Besides HGMSs, basalt fibre was used. Owing to its unique properties, basalt fibre is of great interest as a filler for thermoplastics. Basalt is non-flammable, can be used at temperatures up to 600 C, possesses high, soundproofing, and thermal insulation properties and biological and chemical resistance, and also does not store radiation. Basalts are not harmful to humans or animals [6]. Table 1 gives the comparative characteristics of basalt and glass fibres. MATERIALS AND METHODS The investigation was conducted on PC-010 polycarbonate, MS-VP-A9 hollow glass microspheres, and chopped basalt fibre (1/4 )-KV11. The investigation was carried out on standard type 2 dumbbell testpieces (GOST ) produced by injection moulding. To determine the structure formed, atom force microscopy (AFM) was used because it makes it possible to obtain a true three-dimensional surface relief. In contrast to optical microscopy, AFM gives greater resolution and does not require the application of a conducting metal coating, which often leads to appreciable surface strain, and in contrast to 2015 Smithers Information Ltd. T/15

2 Table 1. The comparative characteristics of basalt and glass fibres Properties Basalt fibre Glass fibre Temperature of application ( C) Sintering temperature ( C) Thermal conductivity (W/(m K)) Diameter of elementary fibre (µm) Tex (g/km) Density (kgf/m 3 ) Elastic modulus Tension set (after heat treatment) : at 20 C at 200 C at 400 C Weight loss of fibre (after boiling for 3 h) : in H 2 O in 2N NaOH in 2N HCl Volume resistivity (Ω) Dielectric loss tangent at frequency of 1 MHz Dielectric permittivity at frequency of 1 MHz Sound absorption coefficient scanning tunnel microscopy, AFM does not use a current between probe and specimen, which can scorch organic compounds. Tests were conducted on an NTEGRA Prima atom force microscope (NT-MDR, Zelenograd, Russia) in contact scanning mode, as in this case a greater noise resistance is achieved by comparison with other methods, and the greatest achievable scanning rate; besides this, AFM is the only method enabling atomic resolution to be achieved. The contact method ensures the best surface scanning quality, with sharp relief gradients, which is very important in the case of specimens with basalt fibre because of the high surface roughness resulting from the large size of the fibre. Testpieces were obtained by the following technology: polycarbonate was predried in an oven at a temperature of 120 ± 5 C for 4 h (HGMSs and basalt fibre were dried in an oven at 70 ± 10 C for 4 h), and then the components were weighed and loaded into a Turbula laboratory mixer (WAB, Switzerland). Mixing was carried out for 15 min. This mixture was then charged into a laboratory extruder for subsequent granulation, after which the specimens were cast on a NEW HAITAI HTW-66 automatic thermoplastics processing machine. The physicomechanical, rheological, and processing characteristics were determined by standard procedures. EXPERIMENTAL At the first stage of the work, we investigated supermolecular formations of unfilled polycarbonate and polycarbonate filled with glass microspheres, and also with basalt fibre. Polycarbonate macromolecules are characterised by greater rigidity, limited rotation of aromatic nuclei, and the presence of comparatively large areas not containing polar groups. In connection with this, polycarbonates have little crystallisation tendency, fairly high glass transition temperatures, and high melt viscosities. Therefore, the crystallisability of polycarbonates depends on their chemical structure, their molecular weight, and, to some degree, their molecular weight distribution. Polycarbonates based on bisphenol A have an amorphous structure, but during processing or service they may partially crystallise [7]. The obtained results of experiments (Figure 1) may indicate that in specimens of unfilled polycarbonate, at a processing temperature of 280 C, fibrillar structures are formed, which correlates well with the results obtained by Marukyan [8]. This, it seems, may be due to the fact that, during melt extrusion, and during subsequent cooling down to 90 C, partial crystallisation occurs; here the polycarbonate is in the glassy state, and, along with short-range order (amorphous regions), regions of long-range order (crystalline regions) appear. The introduction of filler into the polycarbonate changes its supermolecular structure. Thus, when 1 wt% glass microspheres is introduced, the size of the fibrils decreases sharply to nm. Furthermore, the fibrils Figure 1. AFM micrograph of polycarbonate T/16 International Polymer Science and Technology, Vol. 42, No. 7, 2015

3 possibly combine to form parcels (parcel size ~270 nm), which in turn may combine to form sheets because a large number of fibrils retreat into the material, which can clearly be seen in Figure 2 (dimension L2). Likewise, in the given material, radial-type spherulites were evident, which indicates an increase in the degree of crystallinity of the material (Figure 3). Besides this, it was established that, after processing, glass microspheres do not break down, have a constant size, and are distributed fairly uniformly in the matrix. AFM data are presented in Figures 4 and 5. For analysis of the surface, a three-dimensional picture of an area of the specimen was obtained (Figure 6). From the given picture it can be seen that the surface roughness amounts to 1.5 µm, which corresponds to the roughness of the mould in which the specimens were produced. Table 2 presents the physicomechanical parameters of initial polycarbonate and of composites with microspheres. As regards polycarbonate filled with basalt fibre, increase in the degree of filling from 10 to 30 wt% is accompanied with an increase in many indices. The data are presented in Table 3. Increase in the content of basalt fibre evidently leads Figure 4. The size of glass microspheres after processing (microsphere concentration 1 wt%) Figure 2. AFM micrograph of polycarbonate filled with 1 wt% glass microspheres Figure 5. The distribution of glass microspheres in the composite (microsphere concentration 1 wt%) Figure 3. AFM micrograph of radial spherulites in a composite of polycarbonate and 1 wt% glass microspheres Figure 6. The three-dimensional image of an area of the specimen for determining surface roughness 2015 Smithers Information Ltd. T/17

4 to a reduction in the size of the fibrils from ~300 nm (10 wt% basalt) to ~150 nm (30 wt% basalt). This is most likely due to an increase in the degree of filling, which in turn may promote better structure formation of the polymer and a reduction in the size of the supermolecular formations. This assumption is in good agreement with investigations of the properties of composites based on polycarbonate and based on other polymers that were reported by Magazinova and Kestel man [9]. Investigations were made of the productivity of the extruder when HGMSs are introduced. The results presented in Table 4 may indicate that the introduction of HGMSs increases extrudate production, and also lowers melt pulsation, thereby ensuring high stability of processing. In our opinion, the production of composites based on polycarbonate filled both with glass microspheres and basalt fibre is promising. The introduction of basalt fibre will make it possible to increase the characteristics of the material and also greatly reduce shrinkage, while the introduction of glass microspheres will make it possible to reduce internal stresses, and will thereby increase the cracking resistance of the composite material. CONCLUSIONS 1. On the basis of the conducted structural investigations of filled and unfilled polycarbonates, the types and sizes of supermolecular formations in the composites have been established, and the effect of the filler on the formed supermolecular structures has been clarified. 2. The distribution of microspheres in the polymer matrix has been investigated, and it has been established that they do not break down under the action of shear stresses during processing. 3. It was found that, when the supermolecular formations in the composites are reduced, there is an increase in their characteristics, and also a sharp reduction in shrinkage of the composite materials. REFERENCES 1. Review of the World Polycarbonate Market. [Online]. Available: 2. Review of the Russian Polycarbonate Market. [Online]. Available: Table 2. The properties of polycarbonate and a composite with glass microspheres Composite Impact Elongation at break Bending Impact at 30 C stress causing failure elastic modulus Elastic modulus in bend MFI (g/10 min) Shrinkage PC % HGMSs % HGMSs Table 3. The properties of composites based on polycarbonate with basalt fibre Composite Impact Elongation at break Bending Impact at 30 C stress causing failure elastic modulus Elastic modulus in bend MFI (g/10 min) Shrinkage PC wt% BF wt% BF wt% BF Table 4. The productivity of the extruder and the linear speed of the extrudate Composite Extruder productivity Q Linear speed of extrudate V Q (g/10 s) Q (kg/h) (m/s) PC wt% HGMSs wt% HGMSs T/18 International Polymer Science and Technology, Vol. 42, No. 7, 2015

5 3. Simonov-Emel yanov I.D. and Kandyrin L.B., Analytical and Problematical Tasks in the Course Principles of Creating Composite Materials. MIKhM, Moscow, 85 pp. (1999). 4. Simonov-Emel yanov I.D. et al., Structure formation in polymer composites with hollow glass microspheres. Plast. Massy, (11):6 10 (2012). 5. Budov V.V., Hollow glass microspheres. Application, properties, technology. Steklo i Keramika, (7 8):7 11 (1994). 6. Egorova O.V. et al., Polyethylene composites filled with disperse basalt. Plast. Massy, (9):38 39 (2012). 7. Smirnova O.V. and Erofeeva S.B., Polycarbonates. Khimiya, Moscow, pp (1975). 8. Marukyan A.M., The application of polycarbonate coatings for the repair of worn parts of sliding friction assemblies of machinery and equipment for the benefit of ecology and the environment. Author s Abstract of Cand Tech. Sci. Dissertation, Moscow State University of Ecology and the Environment, Moscow, 24 pp. (2003). 9. Magazinova L.N. and Kestel man V.N., Polycarbonate in Engineering. Mashinostroenie, Moscow, 174 pp. (1971) Smithers Information Ltd. T/19

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