Yoosup Park

Publications (4)9.41 Total impact

• Article: The behavior of aged regenerated Bombyx mori silk fibroin solutions studied by (1)H NMR and rheology.

  Zainuddin, Tri T Le, Yoosup Park, Traian V Chirila, Peter J Halley, Andrew K Whittaker
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  ABSTRACT: As part of a project to utilize the regenerated silk fibroin (RSF) membranes as a supporting matrix for the attachment and growth of corneal stem/progenitor cells in the development of tissue engineered constructs for the surgical restoration of the ocular surface, the behavior of the aged RSF solutions has been investigated. The solutions were produced from domesticated silkworm (Bombyx mori) cocoons according to a protocol involving successive dissolution steps, filtration and dialysis. The solutions were kept at 4 degrees C in a refrigerator for a certain period of time until near the gelation time. The changes in molecular conformation were studied by solution-state (1)H NMR, while the flow of the solutions was characterized by rheological method. Upon ageing turbidity developed in solutions and the viscosity continuously decreased prior to a drastic increased near the gelation time. The (1)H resonances of aged solutions showed a consistent downfield shift as compared to the (1)H resonances of the fresh solution. Shear thinning with anomalous short recovery within a certain range of low shear rates occurred in both fresh and aged solutions. While the solutions behave as pseudo-plastic materials, the chain conformation in aged solutions adopted all secondary configurations with beta-strand being predominant.
  Biomaterials 12/2008; 29(32):4268-74. · 7.40 Impact Factor
• Article: Studies on polymers and composites from lignin and fiber derived from sugar cane

  William Doherty, Peter Halley, Les Edye, David Rogers, Francisco Cardona, Yoosup Park, Tim Woo
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  ABSTRACT: Sugarcane fiber (i.e. bagasse) lignin has a larger fraction of aromatics unsubstitution in the ortho position than hardwood or softwood lignin and hence has the greater ability to be derivatized. Furthermore, organosolv lignin has a higher purity than sulfonated and kraft lignins. This work examines the purification of organosolv lignin derived from bagasse and the physico-chemical properties of the lignin and lignin-phenol formaldehyde (PF) resin coatings, and composites.The wetability tests have shown that lignin and lignin-PF resin films are effective water barrier coatings, though the contact angles of lignin-PF resin films were considerably less than the wax films. The overall mechanical properties (i.e. peak stress, peak strain and modulus) of the bagasse fiber composites were lower than the values obtained with the composites without the inclusion of bagasse fiber. Copyright © 2007 John Wiley & Sons, Ltd.
  Polymers for Advanced Technologies 03/2007; 18(8):673 - 678. · 2.01 Impact Factor
• Article: Developing Lignin-Based Resin Coatings and Composites

  Yoosup Park, William O.S. Doherty, Peter J. Halley
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  ABSTRACT: Phenol in phenol formaldehyde (PF) resin has been partly substituted with lignin extracted from sugarcane bagasse. In order to optimize the lignin-based resin for applications in coating and composite materials, thermal and rheological tests were performed with different wt% of lignin substitution into PF resins. Differential scanning calorimetry scans showed a small exothermic peak and a large endothermic peak, typical of resins. The Tg of the resins was seen between 125 and 150 °C and this transition was clearly evident when the lignin content was increased from 10 to 40 wt%. Increasing the lignin content in the PF resin increases the rate of cure and the heat of reaction. Water absorption tests show that the lignin-PF resin films are effective water-barrier coatings for cardboard substrates. It is speculated that the interaction between the substrate and the lignin-PF resin has resulted in a negative surface charge which would have contributed to the reduction in the contact angle.
• Article: The behavior of aged regenerated Bombyx mori silk fibroin solutions studied by 1H NMR and rheology

  Traian Chirila, Peter Halley, Tri Le, Yoosup Park, Andrew Whittaker, Zainuddin Zainuddin