Nascent powder

Figure 1 lH FIDs observed at room temperature for solution-crystallized (A), melt-crystallized (B) and nascent powder (C) samples. 

The nascent powder sample has quite a different morphology compared to the solution-crystallised or melt-crystallised samples. The nascent powder morphology mainly consists of particles connected by fibrils, which is called the "cobweb" structure.26 27 The nascent powder does not have any typical lamellar morphology but has a domain structure where crystalline domains distribute within the whole powder globule (Figure 3C). The domain size has a wide range of several tens of nanometres radius. 

Figure l.28 The beats, showing a combination of intensity drop and subsequent recovery, are clearly observed in the 20-30 /rs region on these FIDs for the higher crystalline solution-crystallised materials and the nascent powder. These two samples undergo a rapid decay, indicating that the solution-crystallised and nascent powder samples are more rigid than the melt-crystallised ones. 

Figure 5 Temperature dependencies of integral widths during heating for solution-crystallized, melt-crystallized and nascent powder samples of UHMW-PE. Changes in both values for crystalline and amorphous relaxations were plotted for each sample.

Crystalline phase Solution-crystallization o Melt-crystallized a Nascent powder... 

Amorphous phase o Solution-crystallized o Melt-crystallized Nascent powder... 

Annealing of the nascent powder sample passed through Process 1, and above 90 °C, dynamic molecular motion started, as defined by Process 2. This critical temperature is slightly higher than that of the solution-crystallised sample. This difference indicates the restricted crystalline chain motion for the domain network structure crystallised during polymerisation. In Process 2, the crystallinity remained at a constant level for the nascent powder sample. This shows that the lamellar thickening is limited for the nascent powder morphology. 

The morphology and molecular mobility of polyethylene nascent powder... 

Nascent powder morphologies of both the nascent and etched samples observed by SEM are shown in Figure 12 for the nascent and 4- and 12-month-etched UHMW-PE powders.24 Unique "cobweb" structures, composed of globules and fibrils, are often observed on the surfaces of nascent PE powders.2 26 27 43 44 In Figure 12A, very few fibrils are observed for the nascent powder. The paste-like morphologies cover the surface of this nascent powder. The major powder structure... 

Figure 12 Scanning electron microscopic images of a series of UHMW-PE samples nascent powder (A), powder treated for 4 months (B) and powder treated for 12 months (C).

The structural change of polyethylene nascent powder upon annealing... 

One of the characteristic of the nascent powder structure is the presence of an intermediate phase included with conventional crystalline and amorphous phases. The higher ductility of polyethylene nascent powders suggested the coexistence of less entangled amorphous phases located between crystalline and amorphous phases.24 4 46 This arises from the non-equilibrium crystallisation during polymerisation. Therefore, the polymerisation temperature affects the structure and the morphology of the nascent powder. 

Figure 17 Comparison of h NMR FIDs observed at room temperature for the nascent powders prepared at Tpo y = 20 °C (A) and 70 °C (B).

TABLE 3 Spin-spin relaxation times T2 calculated as the inverse of the integral width for the nascent powders prepared at 20 and 70 °C... 

The structural development model in Figure 19 is a combination of all the information obtained from TEM observation, WAXD and NMR measurements.46 The results of the morphological changes during annealing demonstrate that the actual polymerisation commenced when the temperature was 20 °C higher than the preparation Tpoiy for each of the nascent powders. This low temperature difference corresponds to an exothermic reaction near the active sites on the catalyst, where continuous chain growth occurs. Rapid crystallisation occurs for... 

Characterization of polyethylene nascent powders synthesized with TpTiCl2(OR) catalysts H OflyS> fi r° cN1 20... 

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