Shape memory polymers for self‐folding via compression of thermoplastic sheets

Abstract

We report a simple method to strain, and thereby program, shape memory polymers by compressing planar thermoplastic sheets. This work is motivated by the limited number of commercially available prestrained polymer sheets; current examples include: Shrinky Dinks, Eastman's Embrace, and polyurethane shrink films. However, these commercial specimens limit the sample thickness, polymer composition, and amount of stored strain. We show here that melt pressing can strain thermoplastic sheets over a range of thicknesses and polymer chemical compositions. After pressing (and thus, straining), the polymer sheets can self-fold out-of-plane into complex geometries using two different actuation mechanisms, both of which locally release strain stored in the polymer. Threedimensional geometries are attained experimentally with both thick (~12 mm) and thin (~1 mm) strained polymer samples with a range of polymer compositions. Digital image correlation maps the strain profile within the melt pressed samples while a Mooney-Rivlin and geometric model predicts the average strain and folding response of the samples, respectively. The model predictions agree well with experimental results. These findings enable self-folding with a broader design space such as polymer chemical composition, sample thickness, strain within the sample, and external stimulus. Techniques presented here should translate to other thermoplastic polymers, thus making this technique a viable tool to increase the available pool of materials available for self-folding devices.

Progress of shrink polymer micro- and nanomanufacturing

“…The folding dihedral angle of a PMMA film could reach up to 180°, capable of enduring a weight of 9 kg. Hubbard et al 82 reported a cube with a thickness up to 12 mm via similar hinge and heating means, confirming the feasibility of this approach.…”

“…6d(iii) . Amber et al 82 also adopted IR light to control the folding angle of a PS sheet with a thickness of 1 mm by patterning ink in hinge regions.…”

Reprogrammable Self-Folding Thermoplastic Sheets Using Elastic Filaments

“…Previously, polymer sheets have been folded using various methods, including light, ,− microwaves, lasers, magnetism, and heat. − These methods can create multiple 3D shapes such as cubes, pyramids, and curvilinear objects . Many of these approaches to self-folding approaches use strain recovery gradients through the thickness of a single sheet of shape memory polymer .…”

Preparation of a high‐performance thermally shrinkable polystyrene SERS substrate via Au@Ag nanorods self‐assembled to detect pesticide residues

“…This creates a shape‐memory effect in the processed plastic, which gives stretched polystyrene molecules more leeway when they are heated and softened again, and they tend to return to their more twisted, shrunken state before stretching. The film, stretched in both directions, contracts more evenly, so that after some magical distortions, the film eventually returns to a nearly flat state, without any visible distortion of the pattern . In 2008, Chen et al used Shrinky Dinks to create tiny structures for microfluidics applications in fields like stem cell research .…”

“…In 2008, Chen et al used Shrinky Dinks to create tiny structures for microfluidics applications in fields like stem cell research . TSP has since been used in both microfluidic and micro/nanodevice manufacturing . TSP can shrink to different degrees according to different heating temperatures and form 3D folds after shrinkage.…”