Two major obstacles to utilizing polyhydroxybutyrate (PHB)—a biodegradable and biocompatible polymer—in commercial applications are its low tensile yield strength (<10 MPa) and elongation at break (~5%). In this work, we investigated the modification of the mechanical properties of PHB through the use of a variety of bio-derived additives. Poly(lactic acid) (PLA) and sugarcane-sourced cellulose nanocrystals (CNCs) were proposed as mechanical reinforcing elements, and epoxidized canola oil (eCO) was utilized as a green plasticizer. Zinc acetate was added to PHB and PLA blends in order to improve blending. Composites were mixed in a micro-extruder, and the resulting filaments were molded into 2-mm sheets utilizing a hot-press prior to characterization. The inclusion of the various additives was found to influence the crystallization process of PHB without affecting thermal stability. In general, the addition of PLA and, to a lesser degree, CNCs, resulted in an increase in the Young’s modulus of the material, while the addition of eCO improved the strain at break. Overall, samples containing eCO and PLA (at concentrations of 10 wt %, and 25 wt %, respectively) demonstrated the best mechanical properties in terms of Young’s modulus, tensile strength and strain at break.

Amines are known to react with succinic anhydride (SAh), which in reactions near room temperature, undergoes a ring opening amidation reaction to form succinamic acid (succinic acid-amine). In this work, we propose to form an amine-responsive polymer by grafting SAh to a poly(lactic acid) (PLA) backbone, such that the PLA can provide chemical and mechanical stability for the functional SAh during the amidation reaction. Grafting is performed in a toluene solution at mass content from 10 wt% to 75 wt% maleic anhydride (MAh) (with respect to PLA and initiator), and films are then cast. The molecular weight and thermal properties of the various grafted polymers are measured by gel permeation chromatography and differential scanning calorimetry, and the chemical modification of these materials is examined using infrared spectroscopy. The efficiency of the grafting reaction is estimated with thermogravimetric analysis. The degree of grafting is determined to range from 5% to 42%; this high degree of grafting is desirable to engineer an amine-responsive material. The response of the graft-polymers to amines is characterized using X-ray photoelectron spectroscopy, infrared spectroscopy, and differential scanning calorimetry. Changes in the chemical and thermal properties of the graft-polymers are observed after exposure to the vapors from a 400 ppm methylamine solution. In contrast to these changes, control samples of neat PLA do not undergo comparable changes in properties upon exposure to methylamine vapor. In addition, the PLA-g-SAh do not undergo changes in structure when exposed to vapors from deionized water without amines. This work presents potential opportunities for the development of real-time amine sensors.

Smart materials that can undergo changes in color upon the detection of amines have the potential to provide information on the freshness of fish and meat.

We present a printable smart material that undergoes a large and reversible change in resistance in response to changes in relative humidity (RH). This material is a conductive polymer composite (CPC), comprised of commercial silver (Ag) microparticles that provides high conductivity to the films, and of a hygroscopic polymer matrix (polyhydroxyethylmethacrylate-co-polyethylene(glycol)diacrylate (HEMA-co-PEGDA)) that responds to humidity by undergoing an increase in volume (through swelling). We characterized the electrical resistivity and swelling behavior of the CPCs, formed sensors comprised of either thin films or patterned lines, and investigated how RH affects the electrical resistivity of the composite films for different compositions and geometries. To characterize the material responsive behavior, a data acquisition system was used to measure changes in resistance while the RH was controlled in a humidity chamber. When the humidity was increased from 25% to 95% RH, the resistance of the films increased up to 650%. Composites with a higher fraction of HEMA in the matrix were found to have both lower recovery times and less hysteresis than composites in which the matrix was pure PEGDA. Such materials can form the basis of inexpensive, printable humidity sensors.