SHAPE MEMORY POLYMERS-(SMPS) NANOSTRIP MULTILAYERS

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SHAPE MEMORY POLYMERS (SMPS) NANOSTRIP MULTILAYERS APPLIED ON THE NEW BEARING GENERATION

FOR HARD WEARING IN TURBOCHARGES

Dr. Eng. Paul OLARU 1, Professor Ian HUTCHINGS 2, Dr. Nicole DORR 3

1 SCO Expert Pool,Salzfassstr 23, Luzern / Switzerland, 2 IfM- Univ. of CAMBRIDGE, UK, 3AC²T-Wr.Neustadt, AUSTRIA

REZUMAT. Polimerii cu memoria formei (SMP) au structura generală constituită din doi componenţi. Un component cu o temperatură de topire ridicată (Tg, temperatura de inflexiune sticloasă) reprezintă componentul dur. Acest component dur (elastomerul) reprezinta elemental principal al SMP-ului. Acesta măreste proprietăţile tribologice (rezistenţa la frecare) și determină o rezistenţă mecanică ridicată la Ttrans – temperatura de tranziţie. La această temperatură, componentul (materialul) plastic (termoplastul) stabilizează componentul dur la temperatură scazută prin scaderea rezistenţei mecanice. Comparând SMP cu SMM – materiale metalice cu memoria formei, SMP au posibilitatea de acumulare și co-regenerare a tensiunii și energiei mecanice (cu până la 200%). Aceste noi materiale SMP sunt mai ieftine, au masa și greutatea mai mici faţă de cele metalice, sunt netoxice și ușor de procesat. Sunt biodegradabile și biocompatibile. Aceste calităţi și proprietăţi fizico-mecanice deosebite impun SMP ca viitoare candidate la realizarea pieselor de lagare din turbo-compresoarele auto și aero.

Cuvinte cheie: polimer cu memoria formei, tribologie, frecare, elastomer, benzi nano.

ABSTRACT. Shape Memory Polymers-(SMPs) nanostrip multilayer’s shows one way effect like shape memory alloys (SMAs). SMPs represent co-polymers which generally the structure consists of two types of components. One component, like nanostrip multilayer’s, with the higher glass transition or melting temperature, represent the hard component. This hard component (elastomer) represent the main element of SMP, which improve the tribological (wearing resistance) properties and provides the mechanical strength of SMP at high temperature, Ttrans, where the soft component (thermoplastic), which stabilizes the hard component at low temperature , loses its strength. Compared to metallic shape memory alloys, SMPs have the ability to store and recover larger strains (up to more than 200%). They are cheap, light in weight, non-toxic, and easy to process. The most important is capacity to be biocompatible and biodegradable. These properties and characteristics offer to SMPs like one potential candidate for future bearings in turbochargers.

Keywords: shape memory polymer, tribology, wear, nanostrip, elastomer.

INTRODUCTION

Biodegradable*polyesters such polyurethane, poly (lactic/glycolic) acid copolymers (PLGA), SMPs based on polycaprolactone, are preferred materials for shape memory polymers.

Their surface hydrophobicity however, triggers the fast clearance of carrier monomers from the body [1, 2].

Surface hydrophilization by immobilization of poly (ethylene glycol) (PEG) might prolong their circulation time and hence allows the programmed SMP release [3].

In the present work thin polymer nano-films on a solid support were used as a model system to study * Această lucrare a fost realizată în laboratoarele IfM – University of Cambridge – UK și D8 DISCOVER, GADDS -BRUKER AXS – Germany.

their surface properties by various techniques. The polymer nano-films were prepared by spin coating casting method from the elastomer mixed with the modifying thermoplast - containing compound at various concentrations.

Wettability and surface analytical techniques were applied to characterize the composition and hydrophilicity of the surface layer.

The increased hydrophilicity and hence the reduced polymers adsorption on the surface is sup-posed to be in correlation with its biocompatibility.

To investigate the poly-elastomer adsorption in situ ellipsometric studies are planned to be performed.

In the present work we show SMPs nanostrip multilayers experiments and results on the nanostrip multilayers sample of the Vybormem-SMP (Figure 1), which is compared with NiTi-shape memory alloys.

This work describes the investigation Tribology Laboratories, IfM – University of Cambridge – UK,

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and D8 DISCOVER with GADDS - BRUKER AXS – Germany.

EXPERIMENTAL RESULTS

Shape memory polymers-(SMPs) nanostrip multi-layers, show a new challange effect against shape memory alloys (SMAs).

Its can be deformed into a new shape and recover to a programmed permanent shape by heating.

The SMPs effect of polymers can be established in different classes of polymers like: polyethylene, polyurethanes and biodegradable, SMPs based on polycaprolactone.

Table 1. The Comparation Shape Memory Polymer-

SMP,Vybormem vs.Shape Memory Alloys

Parameters Shape Memory Polymer –

SMP Vybormem

Shape Memory Alloys –

NiTiX [6] Density, g/cm³ 0,8-1,2 6,3-6,7 Deformation, % Up to 237 8 Young modulus T Ttrans, GPa

0,0088-1,0 72-98

Tensile strength, Yield, MPa

19,0 27,0

Temperature work , ºC (-15) / (+310) (-50) /(+100) Thermal conductivity, W/mK

0,12-0,35 12-18

Biocompatibility /degradability

Can be biocom-patible and / or biodegradable

Good biocom-patible and not biodegradable

Processing conditions Low pressure, 250ºC

High pressure, 1000ºC

Corrosion resistance Excellent Very good Costs 185€/kg 300-360€/kg Hardness, Shore A 75 50-64 Compression set 72 hours @ 200ºC -

Fig. 1. Shape Memory Polymer nanostrip multylayers – Vybormem.

Fig. 2. Shape Memory Polymer-SMP, Vybormem: the nanostrip dimensions: 5 x 25 x 125 nm; presentation of the Shape Memory Polymer after 25 tests, max. Strain 100%.

Fig. 3. Effect of the glass transition.

a)

b)

Fig. 4:

a – electrical; b – friction vs. Temperature for Shape Memory Polymer – SMP, Vybormem.

Fig. 5. Shape Memory Effect of Shape Memory Polymer Nanostrip Multilayer’s, SMP – Vybormem over 46ºC.

Shape memory – probe 2.1

Shape memory – probe 2.1

SHAPE MEMORY POLYMERS-(SMPS) NANOSTRIP MULTILAYERS

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a) Shape Memory Polymer – SMP, Vybormem nanostrip spot front size, low zoom, and spot-size front size.

b) Shape Memory Polymer-SMP, Vybormem nanostrip spot front size high zoom (bn )

Fig. 6

a) SMPs nanostrip multilayer’s covering O-Ring used in bearing turbocharger.

b) SMPs nanostrip multilayer’s covering O- Ring used in the bearing turbocharger after one full test

Fig. 7

DISCUSSIONS

Figure 1, shows physic-chemically evolution of SMPs.

In figure 2 and 3, we show nanostrip real forms of Vybormem coated nano-layer deposed and short flow chart of SMP shape against Tg [4, 5].

Moreover in order to characterize the elastic-plasticity of nano-layers in coated deposition, we show electrical measurements (fig. 4).

The electrical resistance Rez (Ω) against tempe-rature shows damping over a glass temperature Tg

[6]. Table 1, shows real parameters of this new Vybormem SMPs nano-layer material against Clas-sical SMA-NiTinol, well known.

In figure 6 (a and b), it is shown the real coated deposit of nano-layers by new method LVM (Laser Video Microscopy) [7, 8].

Diorama from figure 5 shows evolution of nanostrip layers Vybormem below and up Tg.

In figure 7 (a and b), it is shown one specific aircraft turbocharger device in use with coated nano-layer Vybormem.

Shape memory polymers SMPs are sometimes considered as being smart materials, because they respond to external stimuli.

SMPs show one way effect like shape memory alloys (SMAs).

They can be deformed into a new shape and recover to a pre-programmed permanent shape by heating [6].

It results from the physical properties of the constituents of the polymer structures, chemistry, and morphology (tendency of chains to adapt high entropy configurations, melting and freezing of soft segments in a co-polymer).

Suitable polymer structures / morphologies are obtained using specific processing and programming procedures.

CONCLUSIONS

Shape Memory Polymer-SMP,Vybormem have been prepared by the IfM method through variation of the cooling procedure.

A monomodal elastomer size distribution was obtained by applying a slow cooling procedure, while a fast cooling procedure gave rise to a hierarchically structured bimodal thermoplast size distribution.

It was possible to demonstrate that the hie-rarchically structured polymer exhibited improved shape-memory properties with respect to the shape-recovery rate and the absolute recovery.

As it was found by mechanical and morphological analysis on the macro and micro scale (by using a micro compression device), the hierarchically structured SMPs can store more energy due to microscopic bending of the large structural walls during compression of the SMPs at elevated tempe-ratures compared to the non-hierarchical polymers.

The surface of the nano-layer SMP Vybormem is flat with no apparent features which could be discerned in the optical microscopy.

Further work is required to rationalize this ob-servation and to study the evolution ofthe surface morphology as function of maximum applied strain of cycle number.

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In a next step, the hierarchically structured SMP might be investigated as actively moving scaffold for tissue engineering purposes to mechanically stimulate cells, as it is currently only achieved by external loading through turbo-chargers and the incorporation of magnetic particles might allow a non-contact triggered recovery.

REFERENCES

[1] W. Sokolowski, S. Tan, M. Pryor, Lightweight Shape Memory Self-Deployable Structures for Gossamer Applications, Proceedings of the 45th Structures, Structural Dynamics and Materials Conference; 2004 Apr 19-22; Palm Springs, California, USA: AIAA (2004).

[2] Lendlein, R. Langer, Biodegradable, elastic shape-memory polymers for potential biomedical applications. Science, 296 (5573): 1673-6, (2002).

[3] W. Sokolowski, A.Metcalfe , S. Hayashi, L. Yahia, J. Raymond, Medical applications of shape memory polymers. Biomed Mater; 2(1): S23-7 (2007).

[4] D. Ratna, J. Karger-Kocsis., Recent advances in shape memory polymers and composites: a review. J.Mater, Sci.44, 255, (2008).

[5] M. Behl, A, Lendlein, Actively moving polymers, Soft Matter 3, 56-58, (2007).

[6] H.Hara, E.Yamada, Thermomechanical properties in a thin film of shape memory polymer of polyurethane series, Smart Mater Stuct. 6, 483, (1996).

[7] W.Zhu, M.Xu, Shape memory effect of polyethylene/nylon 6 graft copolymers, Polym, 39, 6930, (1998).

[8] R. Langer, A.Lendlein, S. Kelch, Shape-Memory Polymers, Sci., 296, 1673, (2002).

Despre autori

Dr. Nicole DOERR Principal Scientist, Area Leader, Excellence Center of Tribology

AC2T research GmbH (AC2T) located in Wiener Neustadt (Lower Austria, south of Vienna) was established in 2002. Since then, AC2T has become one of the worldwide largest research institutions in the field of tribology (friction, wear, lubrication). About 150 employees work in four research areas covering the most relevant fields of tribology:

Professor Ian HUTCHINGS GKN Professor of Manufacturing Engineering

Research interests: scientific and technical aspects of inkjet printing; application of tribological principles to manufacturing processes; surface engineering and related manufacturing processes. Background: Professor Ian Hutchings is the GKN Professor of Manufacturing Engineering. He is also a fellow of St John's College, Chairman of St John's Innovation Centre Ltd. and Editor-in-Chief of the international journal, Wear. In 2005 he founded the Inkjet Research Centre in the Institute for Manufacturing in which he and colleagues investigate the science and technology which underpins this important industrial technology.

Dr. Eng. PAUL OLARU EU SETEC- Expert, SCO Consulting GmbH, CH-Luzern, Switzerland

Present activities: Expert Engineer Metallurgist- SCO Consulting GmbH, CH-Luzern, Switzerland Expert Engineer Metallurgist – Continuous Casting ,Rotocasting,HVOF Billets Cutting Blades, ANIELI & C. S.p.A.- ITALY. Scientific Manager, Head Technologic & laboratory team, INCDMNR-IMNR,Romania. Senior Materials Engineer and Tribology, Honeywell Brno, CZECH Rep. Tribo-technology activities and surface engineering (evaluation of materials and coatings);Hand on all tribology-activities on the DN 55-Phoenix Tribology Ltd. Wear machine & Profilometry on the Wyko NT 1100; International collaboration; Built new team international engineers; Failure Analysis Estimator; Quality Manager. Expert and evaluator-developent and implement studies over the continuous casting machines dimensioning steel production working/operating, materials and tests;