Tailoring the Properties of a Shape-Memory Polyurethane via Nanocomposite Formation and Nucleation

Abstract

Thermoplastic polyurethanes (PUs) can display shape-memory (SM) characteristics if their microphase-separated structure, consisting of domains formed by hard blocks and soft segments, respectively, is complemented with the ability of the soft segments to partially crystallize, so that the third phase thus formed can serve as the switching element for the shapememory effect. While property modifications of SMPUs usually require de novo synthesis, we show at the example of a commercially available poly(ester urethane) consisting of crystallizable poly(1,4-butylene adipate) soft/switching segments and hard segments composed of 4,4methylenediphenyl diisocyanate and 1,4-butanediol that the thermomechanical properties can also be modified by formulating nanocomposites and/or influencing the crystallization of the soft/switching segments via the addition of a nucleating agent. The incorporation of cellulose nanocrystals (CNCs) by simple melt-mixing allowed increasing the tensile storage modulus from 150 MPa (neat polymer) to 572 MPa (15% w/w CNCs) while the shape fixity at a specific fixing temperature was increased from 47 to 75%. The temperature at which good fixity (>97%) could be rapidly achieved was increased from 10 to 25ºC upon addition of 1% w/w dodecanoic acid, which served to nucleate the poly(1,4-butylene adipate) crystallization.

Blends of poly(ester urethane)s and polyesters as a general design approach for triple‐shape memory polymers

“…20% was programmed/fixed at 120/65 C and a second temporary shape (shape 2) in which the sample was further elongated to a nominal strain of ca. 40% was programmed/fixed at 65/0 C. The actually programmed strains exceed the nominal values, especially in the first cycle, as common for shape memory experiments carried out under controlled-stress conditions, 11,42 and crystallization-induced elongation was observed in the fixing steps. 36 To trigger the shape recovery, shape 2 was first heated to 65 C, where shape 1 was restored, and subsequently to 120 C, where the original shape was recovered.…”

“…The original shape can subsequently be recovered by exposure to the same or another suitable stimulus. Polymers in which one temporary shape is programmed and released upon heating represent the most‐widely investigated sub‐family of SMPs 11–16 . These materials feature a covalently or physically cross‐linked network that is responsible for elastic deformation and drives the recovery to the permanent shape, and a switching element which turns the deformability of the material on or off, usually via a reversible thermal transition 17,18 .…”

Mechanically adaptive thermoplastic polyurethane/cellulose nanocrystal composites: Process‐driven structure–property relationships

“…The mechanical adaptation for thermoplastic CNC composites and their underlying mechanism have been well documented in several polymer–CNC composite systems . Previously investigated thermoplastic matrices include poly(styrene‐ co ‐butadiene), thermoplastic polyurethane (TPU), polybutadiene, poly(vinyl acetate), cellulose acetate, and poly(butyl methacrylate) as well as thermosetting matrices such as natural rubber (NR) and epoxidized NR . These studies characterize the effect of factors such as hydrophilicity, glass transition temperature, CNC concentration, and charge density on the mechanical reinforcement and switching behavior of the composite .…”

Shape memory properties and unusual optical behaviour of an interpenetrating network of poly(ethylene oxide) and poly(2‐hydroxyethyl methacrylate)

“…Shape memory polymers (SMPs) are a new class of smart materials which can be given a temporary shape and recover their permanent shape on demand using heat or any other external stimuli such as light, electric field etc . The advantage of SMPs over shape memory alloys are that SMPs offer higher recoverable strain and a wider range of mechanical properties .…”

“…Shape memory polymers (SMPs) are a new class of smart materials which can be given a temporary shape and recover their permanent shape on demand using heat or any other external stimuli such as light, electric field etc. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18] The advantage of SMPs over shape memory alloys are that SMPs offer higher recoverable strain and a wider range of mechanical properties. 1,2 For example, a shape memory alloy (Nitinol, Ni-Ti alloy) shows maximum recoverable strain up to 8%, shape memory ceramics show maximum recoverable strain less than 1%, whereas SMPs can show recoverable strain up to 100% and the same can be tailored as a function of composition.…”