Optically transparent poly(methyl methacrylate) with largely enhanced mechanical and shape memory properties via in-situ formation of polylactide stereocomplex in the matrix

c-Perpendicular Orientation of Poly(ʟ-lactide) Films

Poly(ʟ-lactide) (PLLA) films, even of high thickness, exhibiting co-crystalline and crystalline α phases with their chain axes preferentially perpendicular to the film plane (c_⊥ orientation) have been obtained. This c_⊥ orientation, unprecedented for PLLA films, can be achieved by the crystallization of amorphous films as induced by low-temperature sorption of molecules being suitable as guests of PLLA co-crystalline forms, such as N,N-dimethylformamide, cyclopentanone or 1,3-dioxolane. This kind of orientation is shown and quantified by two-dimensional wide-angle X-ray diffraction (2D-WAXD) patterns, as taken with the X-ray beam parallel to the film plane (EDGE patterns), which present all the hk0 arcs centered on the meridian. PLLA α-form films, as obtained by low-temperature guest-induced crystallization, also exhibit high transparency, being not far from those of the starting amorphous films.

Effect of the addition of diurethane dimethacrylate on the chemical and mechanical properties of tBA-PEGDMA acrylate based shape memory polymer network

There is a great demand for the synthesis of acrylate based thermoset shape memory polymer (SMP) associated with one monomer and one crosslinker such as tert-butyl acrylate (t-BA) with poly (ethylene glycol) dimethacrylate (PEGDMA). The present work describes the synthesis of a new thermoset SMP wherein a second monomer such as diurethane dimethacrylate (DUDMA) has been added to the existing tBA + PEGDMA SMP matrix. The synthesized thermoset shape memory polymer exhibited a glass transition temperature (Tg) of 55 °C, higher Young's Modulus of 3.23 GPa, transmittance of 95% and 100% shape recovery. The SMP exhibited response to both thermal and chemical stimuli. The shape recovery rate of the SMP network is 20 s compared to 24 s observed for SMP based on tBA + PEGDMA. The obtained SMP is very transparent and possesses higher stiffness (8 MPa) and hence may be suitable for biomedical shape memory lens and orthopedic application.

Influence of Long-Term Storage on Shape Memory Performance and Mechanical Behavior of Pre-stretched Commercial Poly(methyl methacrylate) (PMMA)

In this paper, we experimentally investigate the influence of storage at 40 °C on the shape memory performance and mechanical behavior of a pre-stretched commercial poly(methyl methacrylate) (PMMA). This is to simulate the scenario in many applications. Although this is a very important topic in engineering practice, it has rarely been touched upon so far. The shape memory performance is characterized in terms of the shape fixity ratio (after up to one year of storage) and shape recovery ratio (upon heating to previous programming temperature). Programming in the mode of uniaxial tension is carried out at a temperature within the glass transition range to one of four prescribed programming strains (namely 10%, 20%, 40% and 80%). Also investigated is the residual strain after heating for shape recovery. The characterization of the mechanical behavior of programmed samples after storage for up to three months is via cyclic uniaxial tensile test. It is concluded that from an engineering application point view, for this particular PMMA, programming should be done at higher temperatures (i.e., above its T_g of 110 °C) in order to not only achieve reliable and better shape memory performance, but also minimize the influence of storage on the shape memory performance and mechanical behavior of the programmed material. This finding provides a useful guide for engineering applications of shape memory polymers, in particular based on the multiple-shape memory effect, temperature memory effect, and/or low temperature programming.

Preparation and Properties of sc-PLA/PMMA Transparent Nanofiber Air Filter

Particulate matter (PM) pollution is a serious concern for the environment and public health. To protect indoor air quality, nanofiber filters have been used to coat window screens due to their high PM removal efficiency, transparency and low air resistance. However, these materials have poor mechanical property. In this study, electrostatic induction-assisted solution blowing was used to fabricate polylactide stereocomplex (sc-PLA), which served as reinforcement to enhance the physical cross-linking point to significantly restrict poly(methyl methacrylate) (PMMA) molecular chain motion and improve the mechanical properties of sc-PLA/PMMA nanofibers. Moreover, the introduction of sc-PLA led to the formation of thick/thin composite nanofiber structure, which is beneficial for the mechanical property. Thus, sc-PLA/PMMA air filters of ~83% transparency with 99.5% PM_2.5 removal and 140% increase in mechanical properties were achieved when 5 wt % sc-PLA was added to PMMA. Hence, the addition of sc-PLA to transparent filters can effectively improve their performance.