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The research presented in this paper investigates the effect of thermally accelerated aging on the submicrostructure of cellulose and attempts to relate such changes to the well‐documented loss of mechanical strength in aged paper. Filter paper and ramie fibers samples were aged in vacuo at 160°C. Small angle X‐ray scattering (SAXS) was used to study void structure within the fibers and hydration used as a structural probe. On hydration, the void radius of gyration and area decrease, while the void aspect ratio and overall void fraction increase. After aging, the wet structure more closely resembles the dry, suggesting that water cannot expand the structure to the same extent. It is postulated that increases in local ordering on aging create a structure more resistant to disruption by water. The use of additional techniques, namely Fourier transform IR spectroscopy, wide angle X‐ray scattering, scanning electron microscopy (SEM), environmental SEM, and measurement of water retention value, provided additional indirect support for the postulated model. There is no direct evidence for significant crystallinity changes in aged material, suggesting that if structural rearrangements occur, they will be local in nature. There is also no evidence for the formation of covalent crosslinks or new chemical species on aging. Water retention values and wet SAXS results concur, highlighting the importance of water in the cellulose structure and the reduced capacity for water sorption in aged samples. SEM observations show that the failure mechanism in paper changes with age from fibers pull out (i.e., interfiber bond failure) to fiber failure, and wide and zero span tensile tests indicate a weakening of the fibers. These results are consistent with previous reports, and we attribute them primarily to chain scission, although the increased intrafiber bonding may have an influence on the values obtained. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 1465–1477, 1999

Sensitivities to the ballistic shock and burn rate characteristics of GAP/AN composite propellants were investigated. Nitrate esters, such as TMETN and NC, were very effective ballistic modifier that provided useable burn rate and pressure rate exponent for minimum signature propellant based on AN. Their low temperature mechanical properties became less sensitive to the temperatures with nitrate esters. Dioctyl adipate platicized propellant showed excellent mechanical properties at operational temperature ranges. The primary initiation mechanism of card gap test was not dominated by the mechanical properties. Although NC significantly increased the critical shock pressure, 14.8% HMX and AP were less effective to the sensitivities. GAP/AN propellants showed excellent IM characteristics to the ballistic shock applied here.

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Small angle X‐ray scattering has been used to study the void parameters of filter paper, kraft paper and ramie after ageing in air and in vacuo at 160 °C and 120 °C. The cellulose fibres contain long thin voids oriented with their long axis roughly parallel to the fibre axis. The aged samples were observed both dry and fully hydrated. Hydration caused small voids to open up between the fibrils which compose a single fibre. The void parameters of dry cellulose remained largely unchanged on ageing, but the wet values of aged material approached those of dry. This effect was more profound the more extreme the ageing conditions. The conclusion is that high temperatures and chain scission encourage chain mobility and facilitate hydrogen bonding between the fibrils in a mechanism similar to that proposed for hornification. Conventional hornification, whereby intrafibre hydrogen bonding increases due to dehydration below a threshold value is also likely. The additional hydrogen bonding means that the fibre is less able to open small voids and absorb water after ageing.Measurements of water retention values of filter paper support the model of structure closure. Zero span and wide span tensile strengths of filter paper fall by greater amounts, the more severe the ageing conditions. The effect of chain scission evidently dominates any internal structural modifications in determining the mechanical strength of aged fibres.© 2002 Society of Chemical Industry