PP/MWCNT/OC Nanocomposites Rheological and Mechanical Properties

Transcription

1 International Workshop, Action COST FA0904 Characterization, Mechanics and Performance of Innovative Polymer Nanomaterials for Food Packaging Application, September 24-25, 2013, Varna, Bulgaria PP/MWCNT/OC Nanocomposites Rheological and Mechanical Properties E. Ivanov, I. Petrova, R. Kotsilkova, C. Silvestre, S. Cimmino, D. Duraccio, M. Pezzuto, G. Mitchell Open Laboratory of Experimental Mechanics (OLEM) Institute of Mechanics (IMech), Bulgarian Academy of Sciences (BAS) Within COST Action FA0904 collaboration with ICTP-CNR, Pozzuoli, Italy (Dr. C. Silvestre, Dr. S. Cimmino, Dr. D. Duraccio and Dr. M. Pezzuto) and CfAM, University of Reading (Prof. G. Mitchell)

2 Content Experimental Rheological Characterization and Structure Termogravimetric analysis Nano-mechanical Properties Conclusions

3 Experimental

4 Preparation of three-phase PP/MWCNTs/Cloisite30B nanocomposites were made in twin screw extruder COLLIN Teach-Line ZK25T during STSM in the Institute of Chemistry and Technology of Polymers (ICTP), CNR, Pozzuoli (NA), Italy. The rheological methods were applied for control of the nanodispersion structure in the nanocomposite melts. The structure of the nanocomposites was analyzed using SEM during STSM in the Centre for Advanced Microscopy, University of Reading. DSC analysis was performed from -80 C to 200 C at 20 C/min in ICTP, CNR, Pozzuoli (NA), Italy. The thermal gravimetric analysis (TGA) was performed in air and nitrogen from 30 C to 800 C at 20 C/min in ICTP, CNR, Pozzuoli (NA), Italy. Nanoindentations were carried out using a Nanoindentation Tester (UNMT) with inline imaging by atomic force microscopy (AFM), produced by Bruker Co.

5 Why Polypropylene? Why Carbon Nanotubes? Why Clay? Why Three-Phase Nanocomposites? Among the most versatile polymers are polyolefin matrices, such as PP, because of their good balance between properties and cost, low density and ease in processability. CNTs have been considered as unique reinforcements for different polymer materials due to their exceptional physical, thermal and mechanical properties. Dispersion of clay nanolayers in polymer matrices usually results to exfoliated and/or intercalated polymer/clay nanocomposite, and this results with improved mechanical and thermal properties. However, hybrid materials that combine two nanofillers particles in a polymer matrix are seldom researched. Researchers reported on extraordinary property enhancement in the case of hybrid nanocomposites incorporating two different nanophases.

6 Nanocomposites Two-phase: 1. PP 2. PP wt% MWCNTs 3. PP wt% MWCNTs 4. PP + 1 wt% MWCNTs 5. PP + 3 wt% MWCNTs Three-phase composites: 1. PP + 12 wt % MA 2. PP + 3wt% Cloisite30B 3. PP wt% MWCNTs + 3 wt% Cloisite30B 4. PP wt% MWCNTs + 3 wt% Cloisite30B 5. PP wt% MWCNTs + 3 wt% Cloisite30B 6. PP + 3 wt% MWCNTs + 3 wt% Cloisite30B

7 Rheological Characterization and Structure

8 Due to the nanometric size and the high aspect ratio of the nanoparticles, the specific surface area is high and thus responsible of strong interparticles interactions which make the dispersion in the matrix difficult. Rheology is one of the indirect methods which is very sensible to the changes of the structure of the nanocomposites and can provide information for both the percolated network structure and the interaction between filler and polymer matrix. In order to evaluate the dispersion structure of the nanocomposites, rheological measurments have been done.

9 Dependence of the storage and loss moduli, G and G on angular frequency for two-phase ipp/mwcnt composites Dependence of the storage and loss moduli, G and G on angular frequency for three-phase ipp/mwcnt/oc composites It is apparent that both the storage and loss moduli of the nanocomposites increase with increase of MWNT content. Specifically in the case of PP and two- and three-phase nanocomposites up to 0.5wt%, at low frequencies PP chains are fully relaxed and exhibit typical homopolymer-like terminal behavior. The G starts to develop a plateau at low frequencies when the nanotube loading reaches 1 wt.%, which is indicative of a transition from liquid-like to solid-like viscoelastic behavior. The solid-like (or pseudo-solid-like) behavior can be attributed to the fact that, as the nanotube content increases in the polymer matrix, nanotube nanotube interactions begin to dominate, eventually lead to percolation and the formation of an interconnected structure of nanotubes in the matrix.

10 Dependence of the dynamic viscosity on angular frequency for two-phase ipp/mwcnt composites Dependence of the dynamic viscosity on angular frequency for three-phase ipp/mwcnt/oc composites The pure PP shows a Newtonian behavior at low frequencies with respect to its viscosity whereas the filled samples exhibit a significant increase in melt viscosity with decreasing frequency. With increasing the MWNT content the viscosity values increase further. The remarkable shift in the shape of the dynamic viscosity plots from pure PP to the composite with 1 wt.% MWNT clearly indicates that a transition from the liquid-like to solid-like behavior has taken place and the systems after 0.5 wt.% MWCNT can be regarded as rheologically percolated.

11 Concentration dependence of the dynamic viscosity, η at low frequency (ω=0.2s-1) of both twophase ( ) and three-phase ( ) ipp nanocomposites The viscosity function changes strongly from linear to non-linear with a sharp slope above 0.5 wt% MWCNTs for the two-phase and three-phase composites. We relate these critical nanotube contents with the rheological percolation threshold, (φ p ). Rheological percolation threshold is determined at φ p =0.5wt% for PP/MWCNT and PP/MWCNT/Cloisite30B composites, respectively.

12 The SEM observations of the filled nanocomposites are presented in order to confirm these results.

13 SEM micrographs at magnification x (CfAM, University of Reading, UK) Two-phase nanocomposites PP + 0.5wt% MWCNTs PP + 1wt% MWCNTs PP + 3wt% MWCNTs

14 SEM micrographs at magnification x (CfAM, University of Reading, UK) Two-phase nanocomposites PP + 0.5wt% MWCNTs PP + 1wt% MWCNTs PP + 3wt% MWCNTs

15 SEM micrographs at magnification x (CfAM, University of Reading, UK) Three-phase nanocomposites PP + 0.5wt% MWCNTs + 3wt% Cloisite30B PP + 1wt% MWCNTs + 3wt% Cloisite30B PP + 3wt% MWCNTs + 3wt% Cloisite30B

16 SEM micrographs at magnification x (CfAM, University of Reading, UK) Three-phase nanocomposites PP + 0.5wt% MWCNTs + 3wt% Cloisite30B PP + 1wt% MWCNTs + 3wt% Cloisite30B PP + 3wt% MWCNTs + 3wt% Cloisite30B

17 Rheological results combined with SEM visualization of the nanostructure could provide further on a preliminary prediction of the effectiveness of nanotube content, where the improvement of the properties of nanocomposites may be expected.

18 Termogravimetric analysis

19 Generally, the addition of nanotubes in the investigated concentration range enhances the thermal stability of ipp in air atmosphere. Importantly, a significant improvement of thermal properties appears at the low filler content of 0.5%, where the TGA curves of ipp/mwcnt composites are shifted significantly toward higher temperatures (with 39 oc), as compared with ipp. Further increase of the nanotube amount (up to 3 wt%) shifted the curves with 65 oc. TGA curves (residual weight vs. temperature) and the corresponding first derivative (DTG curves) in air atmosphere for the two-phase PP/MWCNT composites.

20 The addition of 0.5% and 3% nanotubes has shifted the TGA curves of ipp by 30 and 68 oc toward higher temperatures in air atmospheres, respectively. TGA curves (residual weight vs. temperature) and the corresponding first derivative (DTG curves) in air atmosphere for the three-phase PP/MWCNT/Cloisite30B composites.

21 Thermal degradation of the samples in nitrogen atmosphere is significantly different from that in air. The DTG curve of ipp, shows a mass rate peak at about Tp 339 oc in air, compared with Tp 473 oc in nitrogen; thus, the thermal stability of ipp is prominently reduced. The two- and three phase nanocomposites are more stable than ipp in air atmosphere. There is very small shifting of the curves toward high temperatures from 2 to 7 oc with addition of MWCNT. TGA curves (residual weight vs. temperature) and the corresponding first derivative (DTG curves) in nitrogen atmosphere for the two-phase PP/MWCNT composites.

22 Very small shifting of the curves toward low temperatures from 4 to 12 oc with addition of Cloisite30B. TGA curves (residual weight vs. temperature) and the corresponding first derivative (DTG curves) in nitrogen atmosphere for the three-phase PP/MWCNT/Cloisite30B composites.

23 Nanomechanical Properties

24 Indenter type Berkovich Diamond with Tip Radius 70 nm was used for indentations in force control mode of 100 mn. A series of 48 nanoindentations were performed for each sample. The maximum load was held for 10 s for proving that the viscoelastic contribution was negligible and the Oliver Pharr model was reliable. It was found that the addition of wt% MWCNTs and Cloisite30B shifted the curves to lower penetration depth compared to that of neat ipp, i.e. the nanocomposite material had better resistance to penetration. This evolution evidences a hardening effect in the all tested two-phase and three-phase nanocomposites. Representative load-displacement curves and values of apparent elastic modulus and hardness from nanoindentation tests of pristine ipp and 1 wt% ipp/mwcnt loaded at 100 mn

25 Small addition of MWCNTs results in a significant improvement of the nanomechanical properties. This effect is more pronounced for the three-phase samples where the improvement of the hardness and elastic modulus is of about 26 % and 52 %, respectively. All values measured show experimental dispersion, which is higher in the case of nanoreinforced materials than for the neat ipp. The level of deviation of the experimental results demonstrates the sensibility of the indenter to the inhomogeneity of the composite structure, produced by the presence of MWCNT agglomerates on the surface, when compared to the pristine polymer. Average values of hardness and apparent elastic modulus vs. nanotube content from nanoindentation tests of twophase and three-phase composites

26 These images provide information about the brittle ductile behaviour of materials because rigid ones show sink-in phenomenon in the indentation print and ductile ones show pile-up effect. Both the neat ipp and 1 wt% ipp/mwcnt composites demonstrate low plasticity behaviour, in which pile-up effect was not observed in the line profile across the print. AFM images of prints made on neat ipp, and 1 wt% ipp/mwcnt composite

27 Conclusions

28 In general, rheologically determined percolation threshold could provide preliminary prediction on the effectiveness of the nanotube content, where the improvement of the mechanical properties of nanocomposites may be expected. Two main aspects are considered to be dominant for the mechanical and thermal properties improvement of the as-prepared ipp composites, when the nanotube content increases: (i) the flocculated structure, which is formed by interconnected nanotubes and incorporated ipp matrix; and (ii) the homogeneity of the composites. Based on the significant improvement of thermal and hardness properties at very low nanotube contents, the ipp/mwcnt/cloisite30b composites have a high potential for application as a reinforced and lightweight plastics for packaging and other engineering applications.

29 Publications with acknowledgment to the COST Action FA0904: 1. I. Petrova, E. Ivanov, R. Kotsilkova, Y. Tsekov, V. Angelov. Applied Study on Mechanics of Nanocomposites with Carbon Nanofillers. Journal of Theoretical and Applied Mechanics, ISSN , Sofia, 2013, vol. 43, 3, pp E. Ivanov, I. Petrova, R. Kotsilkova, V. Mihailova. Epoxy/Multi Wall Carbon Nanotube Composites Structure, Viscoelastic and Nanomechanical Properties. Nanoscience and Nanotechnology Letters (2013) (in press). 3. Kotsilkova R, Ivanov E, Mihailova V. Role of Surface Functionalisation of Multiwall Carbon Nanotubes on Nanomechanical and Electrical Properties of Epoxy Nanocomposites. Nanoscience and Nanotechnology Letters, ISSN: , Vol. 4 (11), (2012), pp Kotsilkova R, Ivanov E, Krusteva E, Silvestre C, Cimmino S, and Duraccio D. Evolution of Rheology, Structure and Properties around the Rheological Flocculation and Percolation Thresholds in Polymer Nanocomposites. Chapter 3 In: Ecosustainable Polymer Nanomaterials For Food Packaging. Innovative Solutions, Characterization Needs, Safety and Environmental Issues (Silvestre C, Cimmino S, Eds), ISBN: , Taylor & Francis Group, LLC (2013) pp

30 Thank you for attention!