Shape memory polymers as actuators: Characterization of the relevant parameters under constrained recovery

Abstract

In this work, a shape memory polyurethane is characterized through constrained recovery experiments performed in a tensile testing equipment. The most relevant results obtained are those concerned with the stress released over time during the recovery stage, since they provide quantitative information that can be used in the design of actuators. For this sake, design guidelines are proposed based on the effect of: (i) the programming temperature; (ii) the deformation imposed during the programming stage; (iii) the recovery temperature; and (iv) the manufacturing process used to produce the samples tested (compression molding and Fused Filament Fabrication). The set of experiments performed with compression‐molded samples put in evidence a considerable variety of material responses: (i) the maximum released stress varied from 0.74 to 1.68 MPa; (ii) the time required to attain this stress varied from 47 to 600 s; and (iii) the stress was released as a peak value that relaxed rapidly, or, contrarily, had a lasting effect. Another relevant conclusion is that the 3D printing technique does not affect the shape memory behavior of the material. Having this in mind, the conclusions provided by the compression‐molded samples study can be extended to printed ones.

Digital Light Processing 3D Printing of Soft Semicrystalline Acrylates with Localized Shape Memory and Stiffness Control

“…The stress peaked around the peak melting temperature, providing a maximum recovery stress (σ r,max ) value of 190 ± 37 kPa. From this value, W was calculated to be 94 ± 19 kJ/m 3 using the following equation W = ( σ r , max ) × ( ε r , max ) 2 that assumes a linear relationship between the constrained and unconstrained recovery, as described previously in the literature. , A W of ∼100 kJ/m 3 is within the same order of magnitude as compared to previously reported low modulus (≤50 MPa) shape-memory materials. − Additionally, the stress remaining in the sample once melted (∼30 kPa) is comparable to that observed for a sample deformed to 100% strain starting at 65 °C (Figure S19), again demonstrating excellent recovery behavior while displaying supersoft (<100 kPa) mechanical properties.…”

A review on shape‐memory polyurethane nanocomposites: Focusing on the most important used nanofillers

“…Shape‐memory materials are a classification of novel materials that include shape‐memory alloys, ceramics, polymers, hybrids, and gels. Among them, shape‐memory polymer (SMP) has attracted the most attention from researchers because of its favorable characteristics 1 . Biocompatibility, chemical stability, transparency, low density, biodegradability, and easier processing are some of these characteristics.…”

“…Two‐way SMPs can provide revocable and programmable shape‐switching behavior between two different shapes. On the other hand, multi‐shapes are materials with the capability of memorizing more than one non‐permanent shape, which can be recovered subsequently in an extremely controllable and irrecoverable one‐way manner 1–3 . The programming process of a two‐way shape‐memory polyurethane (SMPU) upon temperature actuation is shown in Figure 1.…”

“…Among them, shape-memory polymer (SMP) has attracted the most attention from researchers because of its favorable characteristics. 1 Biocompatibility, chemical stability, transparency, low density, biodegradability, and easier processing are some of these characteristics. SMPs, moreover, have the remarkable potential to regain their primary shape upon multiple stimulants including laser, radiation, direct or Joule heating, pH, solvent or solvent vapors, moisture, pressure, and microwaves (MWs).…”

“…On the other hand, multi-shapes are materials with the capability of memorizing more than one non-permanent shape, which can be recovered subsequently in an extremely controllable and irrecoverable one-way manner. [1][2][3] The programming process of a two-way shape-memory polyurethane (SMPU) upon temperature actuation is shown in Figure 1. The shape-memory performance of polymers can be determined by two parameters: shape fixity (R f ) and shape recovery (R r ), defined as:…”