Experimental and theoretical approaches in macromolecules design, synthesis, modification and nanosensor applications

Chitosan shows merit as a biomaterial in medical research particularly in terms of its good biocompatibility, but its poor solubility at physiological pH values narrows its potential scope of use. In this first part of this thesis, a freeze-concentrated chemical modification approach was developed to transform chitosan, yielding derivatives with reduced chain regularity and improved solubility. In confirming the generality of this approach, chitosan solutions spiked with acrylic, citraconic, itaconic, or maleic acid were incubated at -10 °C, transforming primary amino groups to the corresponding Michael type adduct. The purified derivatives were characterized via 13CNMR, ATR-FTIR, XRD, ninhydrin, solubility measurements, and SEM, with changes in XRD and ninhydrin profiles particularly correlating well with improved solubility. It follows to reason that this approach enhanced processability of challenging or thermally sensitive biopolymers and contribute to the Michael reactions in the sense our method yields the free acid directly, which is in fact another novelty in chitosan research. In the second part, a molecularly imprinted chitosan and graphene-based nanosensor was fabricated to selectively detect nitrotriazolone (NTO) molecules with a molecularly imprinted film via simple electrical measurements. Molecularly imprinted polymer comprising chitosan was used as sensitive layer. Gold electrodes for electrical measurements were lithographically fabricated on Si/SiO2 substrate, followed by monolayer graphene transfer and polymeric film coating. Monolayer graphene and molecularly imprinted polymer were characterized by ATRFTIR, UV-Vis, SEM and Raman spectroscopy. Transfer-length measurements (TLM) indicate that the sensor selectively and linearly responds against aqueous NTO solutions within a wide range of concentration of 0.01–0.1 mg mL_1 that covers the lowest toxic level of NTO determined by USEPA. This nanosensor with embedded electrodes is re-usable and suitable for field applications, offering real-time electrical measurements unlike current techniques where complex analytics are required. Third part of the thesis deals with theoretical investigation of structure-morphology-property relationship in thermoplastic polyurethanes. Soft segment (SS) chain length is known to affect the morphologies and mechanical behavior of poly(ethylene oxide) based-segmented poly(urethaneurea) copolymers in binary solvents. Here, a multi-scale computational study is carried out to determine the origins of this behavior. First, single chains of a series of poly(ethylene oxide) (PEO) of varying lengths are comparatively examined by molecular dynamics (MD) and dissipative particle dynamics (DPD) simulations in THF:DMF mixture to verify that the coarse graining strategy is applicable to the system at hand. In the second step, hard segment (HS) beads containing urethane groups are attached into PEO chains to study the effect of hard segment on morphology. Density fields obtained from DPD calculations results in a stable channel formation of soft segment molecules in the copolymers with the lower soft segment lengths. Morphologies of copolymers with three different soft segment lengths investigated by DPD are followed by reverse mapping to full atomistic detail. Monitoring the trajectories and the reverse mapped structures, we find that urethane-PEO interactions are significantly stronger in copolymer with lowest soft segment length leading to channel formation. The findings are corroborated by atomic force microscopy (AFM) images obtained for the corresponding copolymers. The strategyemployed in this work lays the foundations for predicting novel morphologies and macroproperties using designs based on HS-SS cooligomers

Water soluble chitosan derivatives via the freeze concentration technique

Chitosan has been an attractive biopolymer for decades, but its processibility is lowered by its poor solubility, especially in physiological pH values. Freeze concentrated reactions of Chitosan with several organic acids including acrylic, citraconic, itaconic, and maleic acid revealed improved solubility and morphological properties. Solubility traits were assessed with a modified ninhydrin test. Chitosan derivatives were characterized by ATR-FTIR and morphological characteristics were determined by SEM. This study is a unique approach to chemically modify Chitosan to enhance water solubility

Investigation of structure-morphology-function relationship of plastomers used to produce low mold shrinkage thermoplastic olefins

Thermoplastic Polyolefins (TPOs) are one of the most commonly used polymeric materials in automotive industry due to their better elastomeric properties compare to commercial polyolefins. Thermoplastic polyolefin (TPO), or olefinic thermoplastic elastomers are prepared by mixing a polyolefin usually copolymer polypropylene and a plastomer in certain fraction in order to improve elastomeric properties. One of the most challenging problems in automotive industry during the production of these materials is to control the mold shrinkage of TPOs since the parts having very high aspect ratio such as bumper, exterior trims, glass run channel are produced by those materials. Therefore, this paper intends to produce TPO formulations with minimum mold shrinkage by focusing on to optimize the mechanical properties. For that purpose, TPO formulations were prepared by melt blending of plastomers having different physical/mechanical properties into a polyolefin phase. The relationship between structure of plastomer and the function of final product TPO was tried to be explained by structural characterization and molecular dynamic (MD) simulations. In terms of mold shrinkage values and mechanical properties the optimum TPO compound is found to be “sample A” containing 70% plastomer with medium crystallinity and 30% copolymer PP. It shows low mold shrinkage values in parallel (0,19%) and perpendicular (0,2%) to flow direction and optimum tensile strength (13,4 MPa), tear strength (74,4N/mm) and elongation at break (815%) results. Findings of this study is useful in understanding the micro-events taking place during compound process of PP with plastomers, and to explain the necessary PP-plastomer ratio with desired mechanical traits

Development and performance evaluation of cool black surface on thermoplastic polyolefins via incorporation of non-near infrared absorptive pigments

Absorption of the near-infrared (NIR) region of solar irradiance spectrum of the sunlight causes increase of the temperature of black inner parts of vehicles. The surface temperature of these parts can be decreased by reflecting or transmitting the NIR region of sunlight. This study intends to decrease the temperature of black surfaces that are exposed to sunlight and create cool black surfaces by preventing the absorption of the NIR region of the solar irradiance spectrum. Incorporation of cool black pigments having NIR reflective or NIR transparent properties into thermoplastic olefins (TPOs) was studied. A series of compounds were generated containing only NIR reflective pigment (REF), only NIR transparent pigment (TRANS) and the mixture of these two pigments in specific loading levels. The surface temperature of black TPO compounds were compared to the TPO compounds containing conventional pigments. Results showed that an optimum TPO compound having cool black surface was obtained with the sample MIX-5 (2% REF + 0.4% TRANS) which demonstrated 28.2% cooling compared to samples with carbon black, 9.04 MPa tensile strength, 1200% elongation at break and mold shrinkage values of 0.61% and 0.11% at directions parallel and perpendicular to flow respectively

Environmentally friendly, antibacterial materials from recycled keratin incorporated electrospun PLA films with tunable properties

The traditional disposal of chicken feathers includes expensive and challenging steps such as incineration and burying in landfills. Keratin is a valuable component of chicken feather waste recycled from poultry industry. The fibrous intermediate protein nature along with unique chemical composition enables its use in food, pharmaceutical, cosmetics and agricultural industries. The current study proposes an innovative valorization of recycled keratin from chicken feathers combined with polylactic acid (PLA), a viable bio-based polymer obtained from plant-based food stock. As a novel application, this study explains the preparation, electrospinning parameter optimization and performance assessment of recycled keratin electrospun with PLA. The structural, thermal, thermo-mechanical, morphological, antibacterial and surface wetting properties of keratin-incorporated electrospun PLA films were investigated. The disruption of crystallinity, hence the processability of both biopolymer via electrospinning is demonstrated. The nanofiber size, thermal, thermo-mechanical, antibacterial and surface wetting properties of electrospun films can be tuned by keratin content. This study provides environmentally friendly, recycled, bio-based material alternatives with tunable material properties that can be used in multitude of applications including environmental food packaging

Insecticide-releasing LLDPE films as greenhouse cover materials

The use of chemical pesticides is limited by several public health concerns regarding their toxicity levels and indiscriminate use. Nevertheless, they are still vital components of agricultural industry since no other competitive equivalents to chemical pesticides still exist in terms of efficiency. This study describes the preparation and biological assessment of an insecticide releasing plasticfilm for agricultural covering purposes. The formulation was prepared by incorporation of deltamethrin loaded, nano-sized halloysite nanotubes into polymeric films. Thermal, morphological, and mechanical properties of films were characterized by Differential ScanningCalorimetry (DSC), Scanning Electron Microscopy (SEM) and Universal Testing Machine UTM. Sustained release profiles of the films were evaluated by Thermogravimetric Analysis (TGA). Results reveal that deltamethrin was successfully loaded into halloysite nanotubes and nanotube incorporation enhances the elastic modulus of linear-low density polyethylene (LLDPE)films. In addition, films exhibit sustained release function of the active agent for 60 days. Bioassays of the nanocomposite films with varying deltamethrin doses tested on grasshoppers showed that theLD50values of the films are−x1.85 105g/cm2. Insecticidal activities of films were tested in greenhouse on Medicago Sativaplants contaminated with thrips and aphid. Nanocomposites are observed to repel mature aphids and kill young aphids and thrips