Resins degradation

At a holdup time longer than 10—15 min at a high temperature, resin degradation is avoided by keeping the rear of the cylinder at a lower temperature than the front. At short holdup times (4—5 min), cylinder temperatures are the same in rear and front. If melt fracture occurs, the injection rate is reduced pressures are in the range of 20.6—55.1 MPa (3000—8000 psi). Low backpressure and screw rotation rates should be used. 

Figure 6.37 Photograph of a segment from a Maddock solidification experiment for a PVDC resin extrusion. The dark band is resin degraded due to a long residence time at the location...

Figure 11.11 Schematic of two transfer line elbows a) a properly designed elbow made by cutting half channels into two metal blocks using a ball end mill, b) a top view of an improperly designed elbow where a single block of metal was drilled from both corners, and c) oblique view of the improperly designed block. Resin degradation products are likely to form in the stagnation positions shown in b)...

Table 11.3 Flight Radii Recommendations to Minimize Resin Degradation at the Channel Edges [20]...

The root cause of dark color streaks in gray-colored parts can sometimes be more difficult to determine since both poorly dispersed pigments and resin degradation products can be the source. In these cases, removing the color masterbatch from the process and operating with just the natural resin will allow the root cause to be identified. That Is, If the dark color streaks still occur in the product after the color masterbatch is removed, then the source of the problem is related to resin degradation. Two case studies are shown in Section 11.12 to illustrate these defects. 

Many of the contamination defects that typically occur in extrusion processes can also occur in injection-molded parts. The most obvious defects are caused by foreign material contamination, resin degradation, and surface defects known as splay. The next sections provide case studies where contamination caused defects in injection-molded parts. 

Extrusion processes are often rate limited by motor power or torque, discharge temperature, or the melting capacity of the screw. Other root causes associated with the design of the screw can limit rates as shown in previous sections. The problems, however, are typically associated with other defects such as flow surging or resin degradation. Chapters 11 and 12 discuss process defects associated with resin degradation and flow surging, respectively. Rate limitations due to inadequate motor power and torque are common problems for commercial plants. Two case studies are presented in the next sections that show rate limitations due to the lack of torque and motor power. 

Oligoester l-2h (G) l-2h (G) Primarily adhesive, but with some resin degradation in cathodic polarization. 19... 

Use of a sterilizing 0.22 ym filter downstream decreased observ able particulates to well below specifications. No resin degradation products were detected in the 25 ml eluate from a 50 mCi generator when tested by GC, HPLC, or fluoroscopy. However, some... 

Thus column resin degradation is minimal and the generator can be safely used for as long as practical levels of radioactivity remain. 

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