18 TH INTERNATIONAL CONFERENCE ON COMPOSITE MATERIALS TRIPLE-SHAPE PROPERTIES OF MAGNETO-SENSITIVE NANOCOMPOSITES DETERMINED IN TENSILE TESTS K. Kratz 1 , U. Narendra Kumar 1 , A. Lendlein 1 * 1 Center for Biomaterial Development and Berlin-Brandenburg Center for Regenerative Therapies, Institute of Polymer Research, Helmholtz-Zentrum Geesthacht, Kantstraße 55, 14513 Teltow, Germany * Corresponding author ( andreas.lendlein@hzg.de ) Keywords : magnetically active nanocomposite, shape-memory polymer, inductive heating, stimuli-sensitve polymer related processes, which is transformed into heat. At the same time, potential changes in the surface to 1 Introduction volume (S/V) ratio of the test specimen during the Shape-memory polymers (SMP) are thermo- [8, 11] , needs to be movement of the sample sensitive materials, which are capable of dual- or considered with respect to heat dissipation (heat triple-shape effect having a high innovation potential loss) at the contact surface exposed to the in different application areas [1-5] . In contrast to a surrounding environment. dual-shape effect, during a triple-shape effect two Recently excellent triple-shape properties could be subsequent shape changes from a first temporary obtained when a two-step bending SMPC was shape (A) to a second temporary shape (B) and from applied for magneto-sensitive switchable triple- there to a third, permanent shape (C) were obtained. shape nanocomposites named MACLC, which were Two essential components of shape-memory prepared by copolymerization of crystallizable polymers (SMP), which exhibit a thermally induced poly( -caprolactone) diisocyanatoethyl methacrylate shape-memory effect (SME), are at least one kind of (PCLDIMA), cyclohexyl methacrylate (CHM) and switching domain related to a thermal transition silica coated magnetite nanoparticles (SNP) [8] . Such ( T trans ) e.g. glass transition ( T g ) or melting transition multiphase polymer network nanocomposites ( T m ) and netpoints, which can be either of physical exhibited an AB polymer network structure. nature (thermoplastics) or chemical nature (polymer In this work we investigated the triple-shape networks). In contrast to intrinsic material properties properties of MACLC using uniaxial-tensile tests, the shape-memory is a functionality, which must be where the SME was activated by environmentally created by a specific thermomechanical treatment of heating, whereby stress-free as well as constant the polymer called shape-memory creation strain recovery modules were utilized. procedure (SMCP), where the temporary shape is fixed after deforming the material [6] . The activation 2 Experimental Part of SME is typically achieved by heat, where the 2.1 Materials desired shape change is achieved when the MACLC polymer networks were prepared by environmental temperature T env exceeds T sw. If copolymerization of PCLDIMA ( T m,PCL = 55 °C) triggering of SME by environmental heating is not with 60 wt% CHM with different SNP nanoparticle possible, non-contact activation is required. One content (0 wt% and 12.5 wt%) according to the opportunity for realization of non-contact SMP method described in [8] . The telechelic crosslinker systems is the incorporation of magnetic particles (PCLDIMA) was synthesized from poly( ε - (e.g. iron(III)oxide based particles) into a SMP caprolactone)diol (Solvay chemicals, UK) with a matrix [7-11] . Activation of the SME in such polymer number average molecular weight of M n = 8.300 composites can be achieved by exposure to an g·mol -1 and 2-isocyanatoethyl methacrylate (Sigma- alternating magnetic field. The inductive heating Aldrich, Taufkirchen, Germany) following the capability of such magnetically active SMP method described in [12] . Benzyl peroxide (Sigma- composites is a result of energy absorption by Aldrich, Taufkirchen, Germany) and silica coated iron(III)oxide particles from the alternating magnetic field via hysteresis loss and/or superparamagnetism
magnetite nanoparticles (AdNano MagSilica, activation module is completed by a waiting period Degussa, Hanau, Germany) were used as received. of 10 minutes at T high . Activation under constant strain conditions For the determination of the maximum stress σ max 2.2 Methods and the corresponding temperature T ,max an The thermomechanical properties of MACLC were activation module under constant strain conditions, analyzed by dynamic mechanical analysis at varied has been carried out after SMCP. The strain level temperatures (DMTA). was kept constant after programming and the A Cyclic thermomechanical shape-memory tests were temperature was increased from T low to T high with the performed on tensile testers Zwick Z1.0 and Z005 heating rate of 2 K · min -1 . The activation module (Zwick, Ulm, Germany) equipped with a thermo was completed by releasing the stress to σ 0 to allow chamber and temperature controller (Eurotherm the sample to recover and a waiting period of 10 Regler, Limburg, Germany) using test specimens minutes at T high . type 1BB ( I 0 = 20 mm, width 2 mm). Every cyclic thermomechanical experiment consisted of a programming module (SMCP), where the temperature-memory is created (see Fig. 1), and a recovery module for activation of SME. For each sample 4 cycles were conducted, whereby the 1 st cycle was maintained as preconditioning and the shape-memory properties were determined as averaged values from cycle 2, 3 and 4. SMCP: The specimen is heated to T high = 150 °C (step 1) with a heating rate of 2 K min -1 and to = 50% T high = 150 °C with 0 elongated from C B an equilibration time of 4 minutes (step 2). For fixation the sample is cooled to T low = -10 °C with a cooling rate of 5 K min -1 under constant stress load resulting in and after a waiting period of 10 B Figure 1: SMPC applied for programming of MACLC. minutes the stress was removed to obtain representing shape (B) (step 3). B 3 Results Afterwards, the sample was heated to T mid = 70 °C Both MACLC materials with 12.5 wt% SNP with a heating rate of 2 K min -1 (step 4), then the (MACLC12) and without nanoparticles = 100% at T mid (step 5), 0 sample was deformed to (MACLC00) showed high gel content values of G > A and subsequently cooled to T low = -10 °C with a 95%, indicating an almost complete crosslinking cooling rate of 5 K min -1 under constant stress reaction. The thermo-mechanical properties of the load whereby the elongation decreases to . Shape investigated polymer networks explored by DMTA A were found to be almost identical. Here two glass , is obtained by unloading (A), corresponding to A transitions could be observed in the tan vs. after a waiting period of 10 minutes (step 6). temperature curve at T max, 1 = -55±3 °C attributed to Activation under stress-free conditions the amorphous PCL and at T max, 1 = 146±3 °C The activation was induced by heating the attributed to the glass transition of the poly programmed sample from T low to T high with a heating (cyclohexyl methacrylate) domains (PCHM), while rate of 2 K · min -1 while the stress is kept at 0 MPa around 50 °C the melting of the PCL crystallites and the sample contracts to recovered shape (B) becomes obvious as displayed in Fig. 2. rec rec at and finally shape (C) at is recovered. The B C 2
Recommend
More recommend
