Mechanical and Surface Properties of Polystyrene Fibers Reinforced with Cellulose Nanocrystals

  • Author / Creator
    Mahsa Kalantari
  • Electrospinning of polystyrene (PS) as a ubiquitous polymer attracted tremendous attention. Though, different reinforcement techniques are commonly considered for the electrospun PS fibers because of their fragile structures. High mechanical properties of Cellulose nanocrystals (CNC) allow these nanoparticles to be used as effective reinforcing materials for a variety of nano-composite applications including electrospun fibers. However, hydrophilic characteristic of CNC makes it less favorable to disperse it uniformly in the hydrophobic polystyrene matrix. Therefore, to improve the interfacial interaction of CNC with polystyrene matrix, CNC nanoparticles were first modified by different functional chemical groups. In this work, three types of modified CNC were used. The modifications included replacement of hydroxyl groups through substitutive reactions with the para nitro benzene, three fluorocarbon benzene, and grafted polystyrenes. Firstly neat PS fibers were optimized by evaluation of the electrospinning solvents, and working parameters. The optimized electrospinning solutions were prepared using DMF as the solvent (20 wt. % of PS (Mn= 250000) was dissolved in DMF). Then, these modified CNCs were used to reinforce PS fibers. Five different loading levels of CNC (0, 0.5, 1, 1.5, 2 wt. % in solid fiber corresponding to 0, 0.01, 0.02, 0.03, 0.04 w/v % CNC dispersion in PS solution) were investigated. Electrospun samples were prepared in two forms of oriented and non-oriented structures. The effects of CNC modifications on the fiber morphologies were initially analyzed through SEM images. Subsequently, results obtained from SEM images were evaluated by turbidity, conductivity and viscosity of electrospinning solutions. The CNC modified with para nitro benzene and para three fluorocarbon benzene resulted in smoother fibers structure and an increase in fibers diameter. On the other hand, beaded fibers, with smaller diameters, were obtained by adding CNC grafted with PS. The effects of CNC inclusion and fiber alignments on the elastic modulus, strength and maximum strain of the fiber mats were investigated by conducting tensile tests. Using DMA results, storage moduli, loss moduli, and damping factors of the electrospun samples were measured and compared. The oriented PS mats with 0.5 wt. % CNC grafted with PS showed the best mechanical gain. The elastic modulus (E) and storage modulus (E’) of this samples increased 910% and 250%, respectively. Finally, alignments of the electrospun fibers led to 450% improvement in stiffness, and 250% increment in storage modulus in avrage with inclusion of 2 wt. % various types of CNC. Finally, the surface properties and wettability of the electrospun samples were studied by means of contact angle and roughness measurements. Three different structures of the neat polystyrene including smooth electrospun fibers, beaded fiber, and electrosprayed spheres, were prepared by using different solvent collections. The beaded fiber structure resulted in the highest contact angle; however, there is a potential for electrosprayed samples to give a rise to superhydrophobic surface after longer times of electrospraying. Moreover, electrospun samples showed the rose petal effect which can be attributed to their hairiness and hierarchical surface structures. Addition of CNC could also change the surface properties due to the changes in roughness, and the surface energy based on the types of the CNC modification. Finally, alignment of the fibers caused a drop in the contact angle and roughness which can be explained by an increase in the structure order for the oriented CNC/PS samples.

  • Subjects / Keywords
  • Graduation date
    Fall 2018
  • Type of Item
  • Degree
    Doctor of Philosophy
  • DOI
  • License
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