Down-chain

Figure 7.9 Mechanisms of laying down chain segments on the growing face of a crystallite a) tight folds with adjacent re-entry, b) independent deposition of chain segments... 

The aim of the Life Cycle Impact Assessment (LCIA) is to facilitate the interpretation of the results of the inventory analysis. The result of the inventory analysis is an emission profile for each alternative system. In this study the emission profile is the total of all emissions to air, water and soil from the grave-to-cradle chain for the use of cushion vinyl floor covering, including the up chain processes, like electricity production and the down chain processes, like the incineration and landfill of the waste. Such an emission profile may consist of hundreds of emissions and extractions. In LCA impact assessment the total of interventions (emissions, extractions) of a process chain is evaluated in terms of environmental problems (impact categories). 

Cellulose II, derived by mercerization of cotton, crystallizes in a monoclinic unit-cell, with a = 0.802 nm, b = 0.899 nm, c = 1.036 nm, and y = 116.6°. The space group is P2,. Two chains, each with a 2(0.518) confonnation, are packed in the unit-cell, with antiparallel polarity. In addition to the OH-3—0-5 (0.269 nm), intrachain hydrogen-bond, an OH-2 —0-6 (0.272 nm), intrachain hydrogen-bond is possible only for the center down chain. This is due to the g+ orientation of the C-6-0-6 bonds in the corner chains and t orientation in... 

Statistical substitution between chains having the same helix handedness, but different orientations of the side groups ("up" and "down chains) was proved or at least suggested as probable for a variety of isotactic vinyl polymers. In particular we will mention here the cases of isotactic polypropylene (53), isotactic poly-w-butene-1 (54), isotactic polyaldehydes (55) and isotactic-1,2-poly-4-methylpentadiene (56). 

Further refinement of the crystal structure consisting of double helices is difficult, because the x-ray photograph is not well-defined, and the possibility of a disordered structure must be considered, e.g., right and left-hand helices, and up and down chains. Although there are some unexplained feature of the double helical model, such as the mode of rapid double helix formation during crystallization, the author and his coworkers believe the result to be essentially correct. 

P2 - parallel "down" chains with the center chain staggered by... 

Figure 3. Structure of Cellulose II (top) (a) ab projection (b) ac projection. (Right,) (c) hydrogen bonding network for the center up chains (d) hydrogen bonding network for the corner down" chains (e) hydrogen bonding in the...

The "upward" curvature in the SV plot (in our case the equivalent plot Q vs. c) which is also "not uncommon" in liquid solution and probably an indication for down chain exciton diffusion according to Webber (62), has been found in Nos. 5-8, 10,11 and 13. Only in No. 12,Q(c) is definitely linear up to Q=5 (7 ) ... 

Fig. 13.—The Unit Cell Proposed by Carlstrom for a-Chitin (Chitin 2). > (The cell is orthorhombic, and has two chains, one up, and the other down. Chains having the same polarity are hydrogen-bonded through planes of C=0-- H—N running perpendicular to the fiber axis.)...

Fig. 17.—Three Possible Arrangements of Chitin Chains. (The chain sense is indicated by arrows. (A) is for chitin 1 (B) and (C) show two possible ways of deriving chitin 2 from chitin 1 by a solid-state transformation. (B) shows up and down chains sliding into each other (C) shows chains folding upon themselves. ")...

The thought then was that in these systems the exciton traveled along the phenyl groups in the side chains of the polymer in a process termed down-chain migration. This view was later confirmed by Fox et al. and David et al., ... 

Down-chain energy migration has since been widely investigated experimentally and confirmed, and is now known to be a common phenomenon that plays a significant role in the degradation and stabilization of polymers, including those... 

In PPDA, the chromophores are part of the polymer backbone, and since they are not adjacent to each other, down-chain energy migration is not possible. Interestingly, when a dilute solution of this polymer is irradiated, a certain amount of excimer fluorescence is observed along with the predominant... 

Figure 2. R factors for parallel-down chains using RMF data. 06 was in the tg position. All five R factors calculated by the SRRC program are shown, calculated at 10 increments of rotation (0 to 180 ) of the corner (rows) and center (columns) chains.

Fig. 6. Probable conversion of the cellulose I crystal structure to that of Na-cellulose I by the action of NaOH. Crystallites are Indicated by boxed-in areas and chains by circles + indicates "up" and - indicates "down" chain directions. The Na" ions are denoted by filled circles. (Reproduced by permission from ref. 8. Copyright 1987 John Wiley Sons, Inc.)...

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