Multiple shape-memory behavior and thermal-mechanical properties of peroxide cross-linked blends of linear and short-chain branched polyethylenes

Abstract

Abstract. Thermally induced shape-memory effect (SME) in tensile mode was investigated in binary and ternary blends of two ethylene-1-octene copolymers with a degree of branching of 30 and 60 CH3/1000C and/or nearly linear polyethylene cross-linked after melt mixing with 2 wt% of liquid peroxide 2,5-dimethyl-2,5-di-(tert.butylperoxy)-hexane at 190°C. The average cross-link density estimated by means of the Mooney-Rivlin equation on the basis of tensile test data was characterized between 130 and 170 mol·m -3 depending on the blend composition. Thermal analysis points out multiple crystallization and melting behavior of blends caused by the existence of several polyethylene crystal populations with different perfection, size and correspondingly different melting temperature of crystallites. That agrees well with the diversity of blends phase morphology characterized by atomic force microscopy. However, triple-and quadruple-SME could be observed only after two-and accordingly three-step programming of binary and tertiary blends, respectively, at suitable temperatures and strains. Compared to performances obtained for the same blend after single-step programming above the maximal melting temperature the significantly poorer characteristics of SME like strain fixity and strain recovery ratio as well as recovery strain rate occurred after multi-step programming. Vol.2, No.7 (2008) [461][462][463][464][465][466][467][468][469][470][471][472][473] Available online at www.expresspolymlett.com DOI: 10.3144/expresspolymlett.2008.56 Strain fixity (R f ) and strain recovery ratios (R r ) are defined according to [4] by Equations (1): (1) where ε p is the strain caused by programming, ε v is the strain that remains after programming, cooling and unloading of specimen and ε rec,m is the residual strain that resides after thermal induced recovery (shrinkage) at maximum temperature of experiment. The investigation of the SM effect of covalent cross-linked semicrystalline polymers and in particular of peroxidic cross-linked ethylene copolymers [7][8][9][10] showed a strong correlation between the melting temperature T m ≡ T trans of the crystalline phase and the response temperature T res , namely T res ≈ T m . Thus, it may be assumed that the existence of several 'n' crystalline phases or/and crystal populations with different perfection, size and correspondingly with distinctly different melting temperatures T m.i in one polymeric material results presumably in a multiple SM behavior, i.e. in the appearance of the same or lower number of recovery strain ε rec (T) steps and accordingly dε rec (T)/dt maxima with response temperatures T res.i ≈ T m.i where 1 ≤ i ≤ n (i is an even number). The triple-shape memory behavior for two different complex polymer network systems which were prepared by photoinduced copolymerization of a methacrylate-monomer and poly(ε-caprolactone) dimethacrylate was already recently described by Bellin et al. [11]. These polymer network systems are formed from two types of chain sections/ domains of ...

Shape-memory behavior of cross-linked semi-crystalline polymers and their blends

“…As an alternative to an expensive synthesis of complex interpenetrating networks and copolymers the multiple SM effects can be also achieved in covalent networks on the basis of polymer blends, if suitable phase morphology can be generated [11][12][13]. The distinct occurrence of triple-shape effect in polymer composites on the basis of electrospun PCL fibers embedded in an epoxy-based copolymer thermoset system was reported by Luo and Mather [11].…”

“…Polymer materials, which reveal multiple SME, are highly innovative smart materials, which permit a number of novel engineering, medical, and pharmaceutical applications [9,10]. Because of great importance of aforementioned applications, SM polymer materials with relatively low switching temperatures (T sw ), which are nearly equal to melting temperatures of their crystalline phases, are a matter of particular interest.As an alternative to an expensive synthesis of complex interpenetrating networks and copolymers the multiple SM effects can be also achieved in covalent networks on the basis of polymer blends, if suitable phase morphology can be generated [11][12][13]. The distinct occurrence of triple-shape effect in polymer composites on the basis of electrospun PCL fibers embedded in an epoxy-based copolymer thermoset system was reported by Luo and Mather [11].…”

Effects of benzoxazine resin on property enhancement of shape memory epoxy: A dual function of benzoxazine resin as a curing agent and a stable network segment

“…Shape memory polymers (SMPs) belong to a novel class of smart materials having been a topic of active research since 1980s, particularly in the past few years [1][2][3][4][5][6][7]. They possess an ability to return from a temporary shape to their permanent shape induced by external stimuli such as light, humidity, solvents, electric or magnetic fields, ionic strength, pH or most typically thermal activation [8].…”

“…In general, SMPs can be either thermoplastics, i.e. polyethylene [2] and polyester [5] or thermosetting polymers such as epoxy [12,13] or polyurethane [14,15]. In case of SMP thermoplastics, their networks can be constructed with physical crosslinks by physical interactions.…”

Shape-memory properties of magnetically active triple-shape nanocomposites based on a grafted polymer network with two crystallizable switching segments

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Shape-memory polymers (SMP) and composites thereof belong to the class of actively moving polymers, which have the capability of storing one (dualshape) [1][2][3][4][5][6], two (triple-shape) [7][8][9][10][11][12][13] or multiple (multiple-shape) [14] stable temporary shapes and recover their original or other temporary shapes when exposed to an external stimulus. The field of SMP research has developed rapidly over the last years [6,[15][16][17][18][19][20][21][22][23][24][25] and it has become apparent that these functional polymers are motivating novel applications.

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