Recycled plastic

When plastics are granulated the probability is its processability and performance when reprocessed into any product may be slighdy reduced; could be significandy rcduced. Fig. 6.10 shows how properties per ASTM tests for different plastics can effect properties of

422 Plastics Engineered Product Design

—1 ej :: Comparison between an analogous model, flow pattern studies

; Comparison between an analogous model, a flow pattern studies with a core added

Figure S. 1C Example of the effect of recycling plastics once through a granulator

Figure 6 Example of the effect of recycling plastics more than once through a granulator

Figure 6 Example of the effect of recycling plastics more than once through a granulator

1st 2nd 3rd 4th

Number of times molded

1st 2nd 3rd 4th

Number of times molded recycled (once through a granulator) plastics mixed with virgin plastics. The data presented are (a) tensile strength, (b) tensile elongation, and (c) unnotched Izod impact test. Fig. 6.11 shows effect on repeating recycling plastics where data presented are (a) tensile strength and (b). Thus it is important to evaluate what the properties of the recycled material provides. The size reduction, and particularly its uniformity, exerts a substantial influence on the quality of the recycled plastics. Recycled plastics is usually nonuniform in size so that processing with or without virgin plastics is subject to operating in a larger fabricating process window (Chapter 1).

Different approaches are used to improve performances or properties of mixed plastics such as: (1) additives, fillers, and/or reinforcements (use specific types such as processing agent, talc, short glass fibers), (2) active interlayers (crosslinking, molecular wetting), and (3) dispersing and diffusing (fine grinding, enlarging molecular penetration via melt shearing).

Most processing plants have been reclaiming/recycling reprocessable TP materials such as molding flash, rejected product, film trim, scrap, and so on during the past century. TS plastics (not remeltable) have been granulated and used as filler materials.

If possible the goal is to significandy reduce or eliminate any trim, scrap, rejected products, etc. in an industrial plant because it has already cost money and time to go through a fabricating process; granulating just adds more money and rime. Also it usually requires resetting the process to handle it alone (or even when blending with virgin plastics and/or additives) because of its usual nonuniform particle sizes, shapes, and melt flow characteristics. Perhaps it was overheated during the cutting acdon of a granulator, etc. Keeping the scrap before/after granulating clean is an important requirement.

When fiber RPs are granulated, the lengths of the fibers are reduced. On reprocessing with virgin materials or alone, their processability and performance definitely change. So it is important to determine if the change will affect final product performances. If it will, a limit for the amount of regrind mix should be determined or no recycled RP is to be used. Consider redesigning the product to meet the recycled performance or use it in some other product.

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