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A spiro diacetal structure based on renewable resources was utilized to synthesize thermosets combining ready recyclability and high performance.

The spinning mechanism of natural silk has been an open issue. In this study, both the conformation transition from random coil to b sheet and the b sheet aggregation growth of silk fibroin are identified in the B. mori regenerated silk fibroin aqueous solution by circular dichroism (CD) spectroscopy. A nucleation-dependent aggregation mechanism, similar to that found in prion protein, amyloid b (Ab) protein, and a-synuclein protein with the conformation transition from a soluble protein to a neurotoxic, insoluble b sheet containing aggregate, is a novel suggestion for the silk spinning process. We present evidence that two steps are involved in this mechanism: (a) nucleation, a ratelimiting step involving the conversion of the soluble random coil to insoluble b sheet and subsequently a series of thermodynamically unfavorable association of b sheet unit, i.e. the formation of a nucleus or seed; (b) once the nucleus forms, further growth of the b sheet unit becomes thermodynamically favorable, resulting a rapid extension of b sheet aggregation. The aggregation growth follows a first order kinetic process with respect to the random coil fibroin concentration. The increase of temperature accelerates the b sheet aggregation growth if the b sheet seed is introduced into the random coil fibroin solution. This work enhances our understanding of the natural silk spinning process in vivo.Keywords: silk fibroin; spinning mechanism; conformation transition; nucleation-dependent; CD spectroscopy.A number of studies have been reported silk processing techniques [1 -11], including those of spider and silkworm. However, the controlling factors that determine the efficiency of silk spinning at ambient temperature and normal pressure remains unclear [6 -8]. The silk fibroin in the silkworm gland possesses relatively low viscosity in a concentrated solution as a result of its storage in a liquid crystalline state before spinning [7 -9]. This is coupled with a low critical shear rate for inducing crystallization in aqueous solution [10], as well as the low draw ratios for the production of uniaxially aligned fibrous structures [11]. Theoretical elucidation of the mechanism for the natural silk spinning process has implications for material science, particularly in the design of engineering polymers.The primary sequence of silk fibroin of the B. mori silkworm predominantly consists of the -(Gly-Ala-Gly-AlaGly-Ser) 8 -motif [12]. It has been demonstrated that two types of conformations exist in the silk fibroin: silk I, a mainly coiled chain conformation in the present silk gland, and silk II which is formed by regularly aligned crystalline b sheet in the silk fibers [7]. Previous studies have suggested that the b sheet conformation can be induced in silkworm fibroin by a stretching force [13], and the formation of spider dragline silk also involves a stress-induced b sheet formation by extensional flow [14]. But the mechanism involved in the conversion of a hydrogel of silk fibroin in the silk I state into the silk II state remains...

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Fully degradable natural fiber/degradable polymer composites have received much research attention and have various applications such as in automotive components. But flammability limits their application; it is important to improve the flame retardancy of fully degradable composites with environmentally friendly flame retardants. Flame‐retarded ramie fiber‐reinforced poly(lactic acid) (PLA) composites were prepared using three processes: (1) PLA was blended with ammonium polyphosphate (APP), and then the resulting flame‐retarded PLA was combined with ramie fibers; (2) ramie fibers underwent flame‐retardant treatment with APP, which were then compounded with PLA; and (3) PLA and ramie, both of which had been flame‐retarded using APP, were blended together. The APP in the composites is shown to be very effective in improving flame retardancy according UL94 test and limiting oxygen index measurements. Thermogravimetric analysis shows that the improved flame retardancy is due to increased char residue at high temperature. The loading of APP disturbs the compatibility between PLA and fibers, which can be directly observed using scanning electron microscopy. Furthermore it has an influence on the dynamic mechanical properties and mechanical properties according dynamic mechanical analysis and mechanical measurements. The results show that composites produced using the third process not only have the best flame retardancy but also comparatively better mechanical properties. Copyright © 2009 Society of Chemical Industry

In the present study, the effects of intumescent flame retardant (IFR) incorporating organically modified montmorillonite (O‐MMT) on the flame retardancy and melt stability of PLA were investigated. The flame‐retardant PLA was prepared using a twin‐screw extruder and a two roll mill. Then, the influence of IFR and MMT on flame retardancy and melt stability was thoroughly investigated by means of limiting oxygen index (LOI), vertical burning test, thermogravimetric analysis, scanning electronic microscopy, melt flow index (MFI), and parallel plate rheological experiments. The experimental results show that the IFR system in combination with MMT has excellent fire retardancy, i.e. the sample could achieve a UL94 V‐0 rating and LOI value increases from 20.1 for pristine PLA to 27.5 for the flame‐retarded PLA. MFI and rheological measurement indicate that O‐MMT significantly enhances the melt stability and suppresses the melt dripping. Copyright © 2009 John Wiley & Sons, Ltd.