http://orion.bme.columbia.edu/lulab/pdf/Altman_Silk-Based-Biomaterials_2003.pdf

Silk-based biomaterials

Silk as a biomaterial

Biological materials: Structure and mechanical properties

Biological degradation of plastics: a comprehensive review.

Plastic is a broad name given to different polymers with high molecular weight, which can be degraded by various processes. However, considering their abundance in the environment and their specificity in attacking plastics, biodegradation of plastics by microorganisms and enzymes seems to be the most effective process. When plastics are used as substrates for microorganisms, evaluation of their biodegradability should not only be based on their chemical structure, but also on their physical properties (melting point, glass transition temperature, crystallinity, storage modulus etc.). In this review, microbial and enzymatic biodegradation of plastics and some factors that affect their biodegradability are discussed.

/pdf/biodegradability-of-plastics-34vbcn0grq.pdf

Biodegradability of plastics.

Dragline silk from the spider, Nephila clavipes, was characterized by thermal analysis (TGA, DSC, DMA), computational modeling, scanning electron microscopy and by quasi-static as well as high rates of strain. Thermal stability to about 230°C was observed by TGA, two transitions by DMA, −75°C, representative of localized motion in the amorphous domain, and a main chain motion associated with partial melt at 210°C. Tensile tests indicated average initial modulus, ultimate tensile strength and ultimate tensile strain of 22 GPa, 1.1 GPa and 9%, respectively. The corresponding properties of the best fibers tested were 60 GPa, 2.9 GPa and 11%, respectively. High strain rates (>50,000%/sec) indicated similar mechanical properties to the average values indicated above. Microscopy showed compressive and tensile strains to failure of 34%. Computational modeling yielded a crystal modulus of 200 GPa.

Mechanical and thermal properties of dragline silk from the spider Nephila clavipes

Processing, performance and biodegradability of a thermoplastic aliphatic polyester/starch system

A series of polyhydroxyalkanoates (PHA), all containing 1% nucleating agent but varying in structure, were melt-processed into films through single screw extrusion techniques. This series consisted of three polyhydroxybutyrate (PHB) and three polyhydroxybutyrate-valerate (PHBV) resins with varying valerate content. Processing parameters of temperature in the barrel (165–173 °C) and chill rolls (60 °C) were optimized to obtain cast films. The gel-permeation chromatography (GPC) results showed a loss of 8–19% of the polymer’s initial molecular weight due to extrusion processing. Modulated differential scanning calorimetry (MDSC) displayed glass transition temperatures of the films ranging from −4.6 to 6.7 °C depending on the amount of crystallinity in the film. DSC data were also used to calculate the percent crystallinity of each sample and slightly higher crystallinity was observed in the PHBV series of samples. X-ray diffraction patterns did not vary significantly for any of the samples and crystallinity was confirmed with X-ray data. Dynamic mechanical analysis (DMA) verified the glass transition trends for the films from DSC while loss modulus (E′) reported at 20 °C showed that the PHBV (3,950–3,600 MPa) had the higher E′ values than the PHB (3,500–2,698 MPa) samples. The Young’s modulus values of the PHB and PHBV samples ranged from 700 to 900 MPa and 900 to 1,500 MPa, respectively. Polarized light microscopy images revealed gel particles in the films processed through single-screw extrusion, which may have caused diminished Young’s modulus and tensile strength of these films. The PHBV film samples exhibited the greatest barrier properties to oxygen and water vapor when compared to the PHB film samples. The average oxygen transmission rate (OTR) and water vapor transmission rate (WVTR) for the PHBV samples was 247 (cc-mil/m2-day) and 118 (g-mil/m2-day), respectively; while the average OTR and WVTR for the PHB samples was 350 (cc-mil/m2-day) and 178 (g-mil/m2-day), respectively. Biodegradation data of the films in the marine environment demonstrated that all PHA film samples achieved a minimum of 70% mineralization in 40 days when run in accordance with ASTM 6691. For static and dynamic incubation experiments in seawater, microbial action resulting in weight loss as a function of time showed all samples to be highly biodegradable and correlated with the ASTM 6691 biodegradation data.

A Processing, Characterization and Marine Biodegradation Study of Melt-Extruded Polyhydroxyalkanoate (PHA) Films

Mechanical Properties of Major Ampulate Gland Silk Fibers Extracted fromNephila clavipesSpiders

Heat transfer and water vapor transport measurements performed at three laboratories using the "sweating" guarded hot plate apparatus were standard ized based on the International Organization for Standardization (ISO) International Standard 11092. Comparison testing was conducted on four standard military uni form materials. The adherence to ISO 11092 resulted in good agreement among the three laboratories between measured values of thermal resistance and water vapor re sistance for the four materials. Factors influencing the accuracy of the test method are also discussed.

Margaret Auerbach

Papers

Mechanical and thermal properties of dragline silk from the spider Nephila clavipes

Processing, performance and biodegradability of a thermoplastic aliphatic polyester/starch system

A Processing, Characterization and Marine Biodegradation Study of Melt-Extruded Polyhydroxyalkanoate (PHA) Films

Mechanical Properties of Major Ampulate Gland Silk Fibers Extracted fromNephila clavipesSpiders

Interlaboratory Evaluation of a New Sweating Guarded Hot Plate Test Method (ISO 11092)