Clarifier fibrils

More work on a detailed description of the fibrillation process is needed to clarify the underlying mechanism and its relationship with molecular aspects, such as the entanglement density or the molecular mobility. Nevertheless, based on the observations reported by DOll [29,30] of time-dependent craze stress and Kramer s [31,32] description of fibrillation involving an active plastic zone, one can conclude that craze thickening is a viscoplastic process. 

The last word has probably not been written about the complex optical properties of collagen. The situation is undoubtedly so difficult that it will be clarified only after more detailed models for fibril structure appear from other directions. At the moment one should conclude from the optical studies that in collagen fibers there are oriented long particles (fibrils), that within these are also regularly arranged thinner elements (protofibrils or molecular chains), and that the particles are penetrable in optically indeterminable ways by chemical agents whose molecules can be of some size. 

SEM micrographs of the wear track clarify the sequence of events leading up to the slip event. Micrographs of typical portions of wear tracks formed at loads of 2 N and 5 N, respectively, are shown in Figure 6. Both wear tracks show plowing and periodic fibril formation along either side of the wear track, where broken fibrils... 

There are probably elements of truth in both explanations. The geometrical explanation for a combination of pointed and fibrillated ends certainly seems valid for the example quoted, but other scenarios could lead to two pointed ends or two fibrillated ends. There may be bias towards different combinations with different forms of Kevlar and Twaron and different test conditions. Examination of a large number of breaks would be needed to clarify the position. Most SEM studies have been limited to the few studies needed to show different, and not necessarily statistically common, forms of break. 

Knowledge of sizes of ciystallites and non-crystalline domains is very important because it allows clarify the models of super-molecular structure of cellulose, in particular of elementary fibrils of cellulose. There are several methods for measuring the size of the crystallites electron microscopy (EM), atomic force microscopy (AFM),WAXS,etc. 

If highly transparent PP is desired, the best clarities and lowest haze values are provided by clarifiers, which by definition are melt sensitive, i.e., they dissolve in the PP melt and re-crystallize upon cooling, thus forming a network of very thin fibrils which then act as nuclei for PP crystallization. Until recently, only dibenzylidene sorbitol and its derivatives were thought to meet the requirements of melt sensitive clarifiers - a paradigm that eventually shifted with the advent of nucleator and clarifier technology based on a non-sorbitol platform [1]. 

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