Molecules, tie

Polymer crystals most commonly take the form of folded-chain lamellae. Figure 3 sketches single polymer crystals grown from dilute solution and illustrates two possible modes of chain re-entry. Similar stmctures exist in bulk-crystallized polymers, although the lamellae are usually thicker. Individual lamellae are held together by tie molecules that pass irregularly between lamellae. This explains why it is difficult to obtain a completely crystalline polymer. Tie molecules and material in the folds at the lamellae surfaces cannot readily fit into a lattice. 

Noncrystalline separating layers of microfibrils are formed from two crystallite surface layers that are side by side in the microfibril and from a central part called the intermediate zones. The latter are mainly made up of tie molecules among which are distinct straightened... 

Figure 2 The lamellar substructure of a fibril. (a) Reciprocal positions of crystalline lamellae as a result of fiber annealing. (b) The situation after relaxation of stress affecting TTM. ai.2 - average angle of orientation of TTM CL - crystalline lamellae CB - crystalline blocks (crystallites) mF -border of microfibrils and F - fibril. In order to simplify it was assumed that (1) there are the taut tie molecules (TTM) only in the separating layers, (2) the axis of the fibril is parallel to the fiber axis.

The tensile strength of PET fibers depends on their superstructure and internal orientation. The results from the investigations by one of the authors [54], show that the value of the tensile strength (o-j) is affected by the fraction of taut tie molecules ()3), the crystallites orienta-... 

For density values g > 0.92 g/cm3 the deformation modes of the crystals predominate. The hard elements are the lamellae. The mechanical properties are primarily determined by the large anisotropy of molecular forces. The mosaic structure of blocks introduces a specific weakness element which permits chain slip to proceed faster at the block boundaries than inside the blocks. The weakest element of the solid is the surface layer between adjacent lamellae, containing chain folds, free chain ends, tie molecules, etc. 

In comparing the correlation sought between MH and E one should emphasize the following while the plastic deformation of lamellae at larger strains when measuring MH depends primarily on crystal thickness and perfection in case of the elastic modulus the major role is played by the amorphous layer reinforced by tie molecules, which is elastically deformed at small strains. Figure 17 illustrates de... 

From the foregoing it is clear that indentation anisotropy is a consequence of high molecular orientation within highly oriented fibrils and microfibrils coupled with a preferential local elastic recovery of these rigid structures. We wish to show next that the influence of crystal thickness on AMH is negligible. The latter quantity is independent on 1 and is only correlated to the number of tie molecules and inter-crystalline bridges of the oriented molecular network. 

Since the increase of the elastic modulus of oriented polymers with draw ratio is, to a large extent, the consequence of the tie molecules or intercrystalline bridges interconnecting crystal blocks within the fibrils 72) one may anticipate a correlation to exist between indentation anisotropy and modulus. Recent data 23) illustrating the... 

Thermally spiked 204 Thermal spikes 195 Three-layer models 152, 174, 175 Three-term models 149 Three-term unfolding model 176,185 Tie molecules 124 Tie-taut molecules 141 Time-dependent hardness 121 Tire cord 6... 

The morphology may be quite complex with consideration of perfectness of crystallinity, orientation of molecules within amorphous regions and tie molecules. 

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