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  • 1
    Electronic Resource
    Electronic Resource
    Properties of poly(styrene)-“grafted” silk fibers and molecular weight of poly(styrene) (1996)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 61 (1996), S. 2197-2205 
    Details
    ISSN: 0021-8995
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Poly(styrene) was grafted onto silk fibers in an aqueous medium, using ammonium persulphate initiator. Add-ons of up to 100% were achieved. The add-on increased linearly with the monomer concentration of the grafting system, all other factors remaining constant. The yield of the reaction attained about 80% and the extent of homopolymerization was negligible. The equilibrium moisture regain decreased noticeably with increasing add-on. Breaking load showed a tendency to increase in the 0-55% range of poly(St) content, while elongation at break and work of rupture decreased. The DSC endothermal peak at 315°C slightly shifted towards higher temperature by graft - copolymerization, and a new endothermal transition appeared beyond 400°C. TG measurements showed an increase of weight retention beyond 300°C for poly(St)-“grafted” silk fibers. The dynamic mechanical behavior was characterized by a shift to lower temperature of the loss modulus peak. The transverse dimension of the fibers increased with increasing add-on. The polymeric residue remaining after alkaline dissolution of silk fibroin showed a porous texture with a sponge-like morphology. The molecular weight of poly(St) removed from silk increased up to 120 kDa in the 0-55% add on range and then remained constant. The “Poly(St)/Silk” molar ratio increased linearly over the add-on range examined. © 1996 John Wiley & Sons, Inc.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Structure and molecular conformation of tussah silk fibroin films treated with water-methanol solutions: Dynamic mechanical and thermomechanical behavior (1998)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 36 (1998), S. 2717-2724 
    Details
    ISSN: 0887-6266
    Keywords: tussah silk ; fibroin ; methanol treatment ; α-helix structure ; β-sheet structure ; dynamic mechanical analysis ; thermomechanical analysis ; Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The thermal response of tussah (Antheraea pernyi) silk fibroin films treated with different water-methanol solutions at 20°C was studied by means of dynamic mechanical (DMA) and thermomechanical (TMA) analyses as a function of methanol concentration and treatment time. The DMA curves of α-helix films (treated with ≥80% v/v methanol for 2 min and 100% methanol for 30 min) showed the sharp fall of storage modulus at about 190°C, and the loss peak in the range 207-213°C. The TMA curves were characterized by a thermal shrinkage at 209-211°C, immediately followed by an abrupt extension leading to film failure. Both storage and loss modulus curves significantly shifted upwards for β-sheet films, obtained by treatment with ≤60% methanol for 30 min. The loss peak exhibited a maximum at 236°C. Accordingly, the TMA shrinkage at above 200°C disappeared. The films broke beyond 330°C, failure being preceded by a broad contraction step. Intermediate DMA and TMA patterns were observed for the other solvent-treated films. The loss peak shifted to higher temperature (219-220°C), and a minor loss modulus component appeared at about 230°C. This coincided with the onset of a plateau region in the storage modulus curve. The TMA extension-contraction events in the range 200-300°C weakened, and the samples displayed a final broad contraction (peak temperature 326-338°C) before breaking. The DMA and TMA response of these films was attributed to partial annealing by solvent treatment, which resulted in the formation of nuclei of β-sheet crystallization within the film matrix. The increased thermal stability was probably due to the small β-sheet crystals formed, which acted as high-strength junctions between adjacent random coil and α-helix domains. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 2717-2724, 1998
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Structure and molecular conformation of tussah silk fibroin films: Effect of methanol (1995)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 33 (1995), S. 1995-2001 
    Details
    ISSN: 0887-6266
    Keywords: tussah silk fibroin ; methanol treatment ; molecular conformation ; crystallization ; Raman spectroscopy analysis ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Structural changes of tussah (Antheraea pernyi) silk fibroin films treated with different water-methanol solutions at 20°C were studied as a function of methanol concentration and immersion time. X-ray diffraction measurements showed that the α-helix structure, typical of untreated tussah films, did not change for short immersion times (2 min), regardless of methanol concentration. However, crystallization to β-sheet structure was observed following immersion of tussah films for 30 min in methanol solutions ranging from 20 to 60% (v/v). IR spectra of tussah films untreated and methanol treated for 2 min exhibited strong absorption bands at 1265, 892, and 622 cm-1, typical of the α-helix conformation. The intensity of the bands assigned to the β-sheet conformation (1245, 965, and 698 cm-1) increased for the sample treated with 40% methanol for 30 min. Raman spectra of tussah films with α-helix molecular conformation exhibited strong bands at 1657 (amide I), 1263 (amide III), 1106, 908, 530, and 376 cm-1. Following α → β conformational transition, amide I and III bands shifted to 1668, and to 1241, 1230 cm-1, respectively. The band at 1106 cm-1 disappeared and new bands appeared at 1095 and 1073 cm-1, whereas the intensity of the bands at 530 and 376 cm-1 decreased significantly. ©1995 John Wiley & Sons, Inc.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/polb.1995.090331402
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  • 4
    Electronic Resource
    Electronic Resource
    Structural analysis of poly(4-hydroxybutyl acrylate)-grafted silk fibres (1996)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 241 (1996), S. 41-56 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Poly(4-hydroxybutylacrylat) poly(4-HBA) wurde aus wäßrigem Medium mit Ammoniumpersulfat als Initiator auf Seide (bombyx mori) aufgepfropft. Die Gewichtszunahme stieg proportional mit der Monomerkonzentration im Pfropfsystem. Der Pfropfgrad lag im Bereich von 45 bis 65%. Die Feuchtigkeitsaufnahme nahm bei einer Gewichtszunahme von 〉10% stark ab. Die mechanischen Eigenschaften der Seidenfasern zeigten mit steigender Gewichtszunahme keine wesentliche Änderung. Doppelbrechung und isotroper Brechungsindex nahmen bis zu einer Gewichtszunahme von 35% ab und blieben dann unverändert. Röntgenbeugungsdiagramme zeigten, daß die kristalline Struktur durch die Pfropfbehandlung nicht modifiziert wird. Kalorimetrische (DSC), thermomechanische (TMA) und thermogravimetrische (TG) Analysen ergaben, daß das thermische Verhalten der poly(4-HBA)-gepfropften Seidenfasern nur leicht verändert wird. Die zur Bestimmung des dynamisch-mechanischen Verhaltens der Seidenfasern durchgeführten DMA-Messungen zeigten eine Verschiebung der E′- und E″-Modulspitzen zu niedrigeren Temperaturen mit steigender Gewichtszunahme. Ablagerungen auf der Faseroberfläche der bei einem hohen Monomer/Seide-Verhältnis (〉50%) gepfropften Seide wurden mit Rasterelektronenmikroskopie nachgewiesen.
    Notes: Poly(4-hydroxybutyl acrylate) poly(4-HBA) was graft-copolymerized onto silk fibres (bombyx mori) in aqueous medium with ammonium persulfate as initiator. The weight gain increased with increasing concentration of monomer in the grafting system. The grafting efficiency ranged from 45 to 65%. Equilibrium moisture regain decreased sharply beyond 10% weight gain. The tensile properties of the silk fibres did not change significantly as a function of the increasing weight gain. Birefringence and isotropic refractive index decreased until 35% weight gain and then remained unchanged. The X-ray diffraction patterns showed that the crystalline structure was not affected by grafting. Differential scanning calorimetry (DSC), thermomechanical (TMA), and thermogravimetric (TG) measurements showed that poly(4-HBA)-grafted silk fibres underwent only slight changes in the thermal behaviour. The dynamic mechanical measurements (DMA) exhibited a downward shift of both the storage (E′) and loss modulus peak (E″) with increasing weight gain. Scanning electron microscopy (SEM) observations showed the presence of some deposits adhering to the surface of silk fibres grafted at high monomer/silk ratio (〉50%).
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/apmc.1996.052410104
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