Fusion time

The critical factor which thus determines the nature of the emerging iron peak is the combustion time. Only a hydrodynamic model can provide us with a full appreciation of fusion times, describing the sudden and brutal temperature increase as the shock wave passes through, and the equally sudden cooling that follows it. 

Processing oils or plasticizers have little solvating effect on UHMWPE at lower temperatures, e.g., at 60°C, but have a significant solvating effect at elevated temperatures, such as 200°C. Lubricants are compounds that, when added to an UHMWPE mixture, improve the processability of the UHMWPE mixture. Improved processability refers to a reduction in fusion time (the time it takes the polymeric system to melt or dissolve into a flowable solution. 

Fusion with Alkali Alone. Alkali lignin was first fused with potassium hydroxide at 180°-190°C. under standard conditions used previously for converting vanillin to vanillic acid (10) and syringaldehyde to syringic acid (14). Under these conditions, protocatechuic and vanillic acids were the chief oxidation products, but over 70% of the lignin was recovered as a lignin-like polymeric product. Longer fusion times helped... 

A great deal of efforts were made to understand the systematics of this new method. Fig. 5 and Table 1 give some such examples. The detail of the analysis can be found in Refs. [29,30]. The resulting DS fusion time spectrum and its comparison with Monte Carlo (MC) simulations are shown in Fig. 6, which clearly establishes the resonance structure. From the time-of-fiight analysis of 2036 116 DS fusion events, a formation rate consistent with 0.7.3 (0.16)meas (0.09)rrto( e times the theoretical prediction of Faifman et al. [9] was obtained (the first error... 

Fig. 4. Simulated correlations between the fusion time and the energy at which molecular formation takes place when there is no fit energy loss in DS layer. Corresponding vibrational excitation in the (dfit)dee system are also shown...

A valuable property imparted by the plasticizer is elongation. Optimization of this property as well as others depends upon adequate fusion time and temperature for thorough plasticization. 

Plasticizers differ significantly in their fusion rates and effects on physical properties. Figure 10 illustrates the differences in solvation between three phthalate plasticizers observed at various temperatures in contact with PVC on a hot-stage microscope. Elongation buildup at 150 °C as a function of fusion time, for three different plasticizers, is illustrated in Figure 11. 

Rotomolding conditions of ethylene tetrafluoro-ethylene (ETFE) polymer are generally similar to those of ECTFE. Table 6.33 shows ranges for temperature and oven (fusion) time for processing ETFE. 

Perfiuoroalkoxy (PFA) pol mier is the most difficult to fabricate by rotomolding because of its high melt viscosity. Table 6.33 shows the temperature and oven (fusion) time ranges for processing PFA. Some specific examples of rotational molding and lining are described here. 

Di(2-ethyl hexyl) phthalate (DOP) and diisooctyl phthalate (DIOP) are largely used for PVC and copolymers of vinyl chloride and vinyl acetate as they have an affinity to these polymers, produce good solvation, and maintain good flexibility of finished products at low temperature. The use of M-octyl-n-decyl phthalate in the production of plastics materials also allows good flexibility and ductility at low temperature. Diisodecyl phthalate (DDP), octyl decyl phthalate (ODP), and dicapryl phthalate (DCP) have a lower solvency and are therefore used in stable PVC pastes. Butyl octyl phthalate (BOP), butyl decyl phthalate (BDP, and butyl benzyl phthalate (BBP) have a good solvency and are used to adjust melt viscosity and fusion time in the production of high-quality foams. They are highly valued for use in expandable plasticized PVC. 

Following the trend of using PVC as matrix, research on the use of EFB as composite in PVC matrix was also reported. Bakar et at [37] used the EFB as filler in unplasticized poly(vinyl chloride) (PVC-U). They studied the effects of extracted EFB on the processability, impact and flexural properties of EFB/PVC-U composites. PVC-U resin, EFB and other additives were first dry-blended using a heavy-duty laboratory mixer and then milled into sheets on a two-roll mill before being hot-pressed and cut into impact and flexural test specimens. There were two kinds of EFB used in this experiment, which were extracted and xmextracted. The FTIR showed that the unextracted EFB contained oil residue, while the extracted one contained less oil residue. The results showed that both extracted and unextracted EFB decreased the fusion time and melt viscosity. However, the fusion time increased with the increase of extracted EFB content. Meanwhile, there was no significant difference in both the impact and flexural properties of extracted and xmextracted EFB. 

A paper presented at the 1990 SPE ANTEC (5) discussed techniques for compounding highly filled polymers with corotating twin-screw extruders. The fusion time as measured in a torque rheometer of 40 wt% filled polypropylene with melt flow index (MFI) of 15 was 2.4 min for glass fibers, 8 min for mica, and 13.5 min for talc. For a 30 wt% loading of mica, fusion time was reduced to about 5 min. 

Branched chains have a faster fusion time. 

Fig. 6. Fusion time of plasticized PVC. Jacket temperature 96°C rotor speed 63 rpm.

The vesicles are oriented between two electrodes of 100 jjm distance applying a field strength of 2-4 kV/cm. The diameter of the two large vesicles is about 40 jjm (fig.21 a). Fusion is initiated by a field pulse of 30-90 kV/cm and 20-50 jjs duration. The intermingling of membrane lipids occurs within a fraction of a second. The membrane boundary between the two vesicles disappears forming an oval as shown in fig, 21 b. A special liposome is formed after turning off the external field. If the vesicles are unilamellar the whole fusion process is completed within one second. In the case of multilamellar vesicles the fusion time is extended to about 3-6 seconds. Fusion times for cells are usually in the range of minutes (35). 

Butyl octyl phthalate (BOP), butyl decyl phthalate (BDP), and butyl benzyl phthalate (BBP) are mixed together to obtain special creep properties or to modify the processibility of PVC blends. These plasticizers have a good solvency and they are used to adjust melt viscosity and fusion time in the production of high-quality foams. 

The oven dwell time is the length of time that the mold containing the resin spends in the oven, known as the oven residence cycle. The time elapsed in the oven can be divided into two parts build-up time and fusion time. The mold heats up and reaches the melt temperature of the resin during the build-up time. The part is formed on the wall of the mold during the fusion time. 

Fusion time is dependent on a number of parameters that are similar to those influencing the build-up time, but not all the same variables are in the same order. They have been listed in Table 9.6 in the order of importance. The first two variables have a drastic influence on the fusion time. It is directly proportional to the wall thickness of the part, which is specified by its intended application. This means that, at a given temperature, to double the wall thickness of the part, the fusion time must also be doubled. Oven temperature has a large impact on the cycle time. Increasing the mold temperature by 100°C can increase the fusion rate by as much as 25%. 

One trick to lengthen the fusion time is to delay cooling after the mold has been taken out of the oven. The large thermal capacity of the mold stores a great deal of heat that will continue heating the resin for some time. The advantage of this approach is to shorten the oven cycle and increase throughput. 

As the particle size of the molding powder is increased, a longer fusion time is required to obtain a surface smoothness equivalent to that of a smaller particle size powder. The likely cause of less efficient heating is the reduced contact surface area between the wall of the mold and the powder. 

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