RELATING PERFORMANCE AND STRUCTURE OF NANOCOMPOSITES BY NEW METHODS - PDF document

18 TH INTERNATIONAL CONFERENCE ON COMPOSITE MATERIALS RELATING PERFORMANCE AND STRUCTURE OF NANOCOMPOSITES BY NEW METHODS IN TIME-RESOLVED X-RAY SCATTERING . Stribeck N * , A. Zeinolebadi, M. Ganjaee Sari Dept. of Chemistry, University of Hamburg, 20146 Hamburg, Germany * Norbert Stribeck( norbert@stribeck.de ) Keywords : Nanocomposites, CNT, SAXS, mechanical loading Abstract . Small-angle X-ray scattering (SAXS) glass fibers must be minimized. Thus, carbon has been used to monitor slow mechanical tests nanotubes or graphenes bonded with PP could of polypropylene and a nanocomposite contain- become an economical alternative. ing multi-wall carbon-nanotubes. By comparing In service, materials are frequently subjected to the extracted evolution information on nano- strain or cyclic loading. Hence, resistance [5] to structure to the mechanical data it has been dynamic load (i.e. low fatigue [6–8]) is required. found that the moderate improvement of mechanical properties (change from necking to There is abundant experimental literature on the homogeneous straining) appears to be related to relation between materials structure and mechanical an increased extension of crystalline lamellae load [9]. Nevertheless, the number of papers in and to an inhibition of nanostructure fatigue in which scattering is studied simultaneously during the composite. In the oral presentation we will fatigue tests is still small [10,11]. Fortunately, recent compare these results to nanocomposites in progress at synchrotron x-ray radiation facilities which CNT is replaced by layered silicates. In makes it possible to follow the variation of this case the crystallites in the nanocomposites anisotropic scattering patterns of polymers during are not bigger, but many small crystallites are mechanical tests with sufficient accuracy. observed (nucleating effect of layered silicates). 1 Introduction 2 Experimental Polypropylene [1] (PP) is the material preferred Materials. [2] by automotive industry for replacement of Isotactic polypropylene (PP) and a composite metal by plastics for reduction of weight and (PP+CNT) from 99.9 wt.-% PP and 0.1 wt.-% fuel consumption. As it comes to weight reduc- multi-wall carbon nanotubes (CNT) have been tion of load-bearing components, the materials studied. properties of the polymer are insufficient. A Components. problem solution is the use of hybrid modules Isotactic polypropylene (PP) from Lyondell- Basell has been used. The grade is Moplen HP from PP and metal that cause high production 400R (density 0.90 g/cm 3 , melt flow rate 25 g/ cost. One could get around the cost if one would 10 min, melting temperature 161 ° C). The succeed to develop an easily processable, low- commercial CNT-grade is obtained from MK fatigue PP-based composite. Glass-fiber rein- Nano, Canada (MWCNT, +95% Pure, OD: forced PP-composites [3,4] are well introduced 10-20 nm, -OH functionalized, -OH content 3.06 et%, specific surface >200 m 2 /g, lot and exhibit advanced properties. Nevertheless, the production of the molded parts is still #0420). The length of the nanotubes is 30 µm. elaborate, because at least the rupture of the

Nanocomposite performance-structure relation by X-ray scattering monitoring of mechanical tests ε=  ℓ − ℓ 0  ∕ℓ 0 Composite preparation. local strain is computed The mixture of PP and CNT has been automatically [14] from the average initial compounded twice into pellets using a Prism distance, ℓ 0 , of the fiducial marks and the Eurolab 16 twin-screw extruder operated at 300 respective actual distance, ℓ . The true stress, rpm, a temperature of 200 ° C, and a feeding σ=F∕A , is computed from the force F rate providing approximately 1/3 of the max. measured by the load cell after subtracting the torque of the extruder. The screws have been set force exerted by the upper sample clamp, and in a strong configuration with 3 mixing zones A=A 0 ∕  1 +ε  , the estimated actual sample having 90 ° spaced mixing disks as part of the cross-section. A 0 is the initial cross section of zone. the central zone of the test bar. The equation Injection molding. assumes conservation of sample volume. Test bars S3 according to DIN 53504 have been In the load-cycling experiments the injection molded in a MiniJet II (Thermo Scien- samples are pre-strained by 1 mm. After that the tific) from a melt of 200 ° C. Mold temperature: cycling starts. In each cycle the samples are 30 ° C, molding pressure: 650 bar, molding strained by 0.5 mm and retracted by the same draw-path thereafter. time: 45 s. holding pressure: 100 bar. Holding time: 20 s. The cross-section of the parallel SAXS setup. central part is ca. 2 mm 1 mm. Small-angle X-ray scattering (SAXS) is carried out in the synchrotron beamline A2 at HASY- LAB, Hamburg, Germany. The wavelength of radiation is 0.15 nm, and the sample-detector distance is 3031 mm. Scattering patterns are collected by a 2D marccd 165 detector (mar research, Norderstedt, Germany) in binned 1024 1024 pixel mode (pixel size: 158.2 µm 158.2 µm). Scattering patterns are recorded every 30 s with an exposure of 20 s. The scattering patterns are normalized and back- ground corrected [15]. This means intensity normalization for constant primary beam flux, Figure 1: PP+CNT. Setup tensile tester in the zero absorption, and constant irradiated volume synchrotron beamline A2 at HASYLAB, Hamburg V 0 . Because the flat samples are wider than the primary beam, the correction has been Tensile testing. carried out assuming Tensile testing is performed in a self-made [12] V  t  ∕V 0 = 1 ∕  1 +ε  t  0.5 . The equation machine mounted in the synchrotron beam (Fig. 1). A grid of fiducial marks is printed on assumes constant sample volume. the test bars [13]. The clamping distance is 30 SAXS data evaluation. mm. A 100 N load cell is used. Signals from The scattering patterns I  s  =I  s 12 ,s 3  are load cell and transducer are recorded during the transformed into a representation of the nano- experiment. The sample is monitored by a TV- structure in real space. The only assumption is camera. Video frames are grabbed every 10 s presence of a multiphase topology. The result is and stored together with the experimental data. a multidimensional chord distribution function The machine is operated at a cross-head speed (CDF), z  r  16. The method is exemplified in of 0.167 mm/min. Using the fiducial marks the 2