Extrusion Scrap

Extrusion processes can generate several types of scrap, including out-of-specification material, material generated when the process is not running at steady state, and edge trim vhen sheet or film is trimmed to the required width. In extrusion, the scrap can be reintroduced to the material stream and reincorporated into the manufactured products. As with injection molding, the form of the scrap often differs substantially from the starting resin. 

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Co-extrusion scrap will become a polymer blend. Other materials will be re-used as... 

Thus thermoplastic elastomers can be processed using conventional plastics techniques, such as injection molding and extrusion scrap can be recycled. Additionally, some thermoplastic elastomers are soluble in common solvents and so can be processed as solutions. 

Insistence on all dimensions as critical will result in the process being restricted to one narrow set of operating conditions, usually at a low production rate, with a high scrap rate and high product costs. In cases where the dimensions are critical, it may be that the extrusion process should be discarded in favor of molding or machining of the product. However controlling all dimensions can be accomplished at a cost. 

Polyurethane materials are extremely versatile in that it is possible to produce a large variety of structures which range in properties from linear and flexible to crosslinked and rigid. The crosslinked PURs are thermosets, which are insoluble and infusible and therefore cannot be reprocessed by extrusion without suffering extensive thermal degradation. At present, the main sources of recyclable waste are flexible PUR foams and automobile waste. Waste and scraps of these materials may consist of 15-25% by weight of total PUR foam production. 

Addition of scrap rubber in the form of either ground waste vulcanizates or reclaim in rubber compounds gives economic as well as processing advantages. In addition to lowering the cost of rubber compounds, the use of cross-linked rubber particles has beneficial effects such as faster extrusion rate, reduced die swell, and better molding characteristics. 

Film recycling is particularly troublesome because of the high surface area of the scrap. Moisture, air, and dust can easily become entrained in the material, introducing potential problems in the extrudate. To address these issues, vent ports and fine mesh screens are often incorporated to the extrusion system to release volatiles and trap solid contaminants. 

Pyromellitic dianhydride (PMDA) is generally used in PET at concentrations ranging from 0.05 to 2%. Reactive extrusion of PET with PMDA has been reported by Incamato et al. [9], These authors used PMDA to increase the molecular weight of PET industrial scraps sourced from a PET processing plant. They found that concentrations of PMDA between 0.50 and 0.75 % promote chain extension reactions that lead to an increase of MW, a broadening of the MWD and branching phenomena which modify the PET scrap in such a way that makes... 

A third evaluation which can be applied to good effect to describe the processability of the polymer is a variable-load melt viscosity measurement. A precaution here is to conduct this test last, on the scraps left over from other physical testing, since the temperature in the rheometer may degrade the precious material irreversibly. A variable-load capillary rheometer simulates extrusion and may thereby provide the strand for evaluation of qualitative... 

Computer-controlled automatic profile dies with electrical controlled sensors in closed-loop control systems have developed greater efficiency and accuracy to extrusion coating, cast film, and sheet lines. A scanner measures the web thickness and signals the computer, which then converts the readings to act on thermally actuated die bolts. The individual adjusting bolts expand or contract as ordered by the computer to control the profile. The more sophisticated systems measure adjusting bolt temperature and provide faster response time with less scrap and quicker startups. The scanner is typically an infrared, nuclear, or caliper-type gauge. 

POSTER TITLE Purification of Aluminium Alloy Scrap by Backward Extrusion Process in the Semisolid Condition... 

EFFECTS OF REPEATED EXTRUSION ON THE PROPERTIES AND DURABILITY OF RIGID PVC SCRAP... 

Table 17.27 describes neat HDPE and some regrinds (scrap and returns from the held) that were combined to make composite deck boards. Four combinations of said ingredients were used (as listed in Table 17.27), and all four resulted in problem extrusion runs. Boards were slightly distorted, pitted, and rough inside. Besides, a few more assorted ingredients are listed in Table 17.27, which might have been resulted in problem runs. 

Co-extrusion blow molding represents a commercially viable technology that has hampered the wide commercial acceptance of the Selar technology. However, increasing needs to recycle production scrap and post-use waste might improve its market penetration. 

ABS/PP alloys have high acceptability in automotive applications because their parent components are already extensively used for interior applications, so they do not introduce any new components into the recycle stream. Thus, the ABS/PP alloy supply would derive partially from recycled interior scrap that has been blended and compatibilized in a reactive extrusion. Virgin materials would probably be added to upgrade performance. Pricing is critical, which may limit the options for compatibilization, which is not straightforward. 

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