Abstract
Shape Memory Polymers (SMPs) exhibit the intriguing ability to change back from an intermediate, deformed shape back to their original, permanent shape. In this contribution a systematic series of t-butylacrylate-co-poly(ethyleneglycol) dimethacrylate (tBA-co-PEGDMA) polymers have been synthesised and characterised prior to incorporation of organoclay. Increasing the poly(ethyleneglycol) dimethacrylate (PEGDMA) content in increments of 10% increased the storage modulus from 2005 to 2250MPa, reduced the glass transition temperature from +41 to −26°C and reduced the intensity of the associated tan δ peak. The tBA-co-PEGDMA crosslinked networks displayed useful shape memory properties up to PEGDMA contents of 40%. Above this PEGDMA percentage the materials were prone to fracture and too brittle for a realistic assessment of their shape memory capability. The system containing 90% t-butylacrylate (tBA) and 10% PEGDMA was selected as the host matrix to investigate how the incorporation of 1 to 5mass% of a benzyl tallow dimethylammonium-exchanged bentonite (BTDB) influenced the shape memory properties. X-ray diffraction data confirmed that BTDB formed a microcomposite in the selected matrix and exerted no influence on the storage modulus, rubbery modulus, glass transition temperature, Tg, or the shape or intensity of the tan δ peak of the host matrix. Therefore, it was anticipated that the presence of BTDB would have no effect, positive or negative, nor on the shape memory properties of the host matrix. However, it was found that the incorporation of clay, especially at the 1mass% level, significantly accelerated the speed, compared with the clay-free SMP, at which the microcomposite returned to the original, permanent shape. This accelerated return to the permanent shape was also observed when the microcomposite was coated onto a 100μm PET film.
Highlights
Shape memory polymers (SMPSMPs) have the ability to store a permanent shape and be deformed into a temporary shape by applying an external stress and temperature
The equilibrium swelling ratios, q, for the networks, t90/P10 to t0/P100, in propan-2-ol decreased as the amount of poly(ethylene glycol) dimethacrylate (PEGDMA), the cross-linking agent, increased (Fig. 4) confirming that the covalent cross-links acted to prevent polymer expansion and swelling
TBA90/PEGDMA10/BTBD 1 P t90/P10/BTBD 1 P. Overall these results indicated that as the PEGDMA content increased there was a corresponding increase in the θ1/2 Final and θFinal Times of recovery
Summary
Shape memory polymers (SMPSMPs) have the ability to store a permanent shape and be deformed into a temporary shape by applying an external stress and temperature. The transformation from the stressed temporary shape back to the permanent, stress-free shape is usually triggered by thermal (Liff et al, 2007), electrical (Liu et al, 2009), or other environmental stimuli e.g. UV or visible radiation (Jiang et al, 2006). This change from temporary to permanent shape is essentially driven by the elastic strain stored in the dormant shape during the initial deformation into the temporary shape (Liu et al, 2007). The unique, ‘tunable’ properties of SMPSMPs make them attractive for a number of potential applications in almost every avenue of life, ranging from self-repairing car bodies
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