Recycling recycled resin

Franklin Associates (2010). Final Report. Life cycle inventory of 100% postconsumer HOPE and PET recycled resin from postconsumer containers and packaging. 

For recycled resins, according to the form and cleanness, the price range is roughly 0.5 up to 1 per kg. 

The bulk density of the feedstock at ambient temperature and pressure should be measured prior to the design of a new screw, especially if it contains in-plant recycle resin. The measurement method is extremely simple and requires only a calibrated cell and a scale. A calibrated measuring cell with a volume of 500 cm can easily be constructed by welding a thin-walled metal pipe to a flat sheet of metal, as shown in Fig. 4.2. The bulk density is measured by filling the cell with feedstock, leveling the top with a steel ruler, and then weighing the cell contents. A more formal measurement technique was developed by ASTM as standard method D1895. 

For recycle, cured specimens were cut up with a band saw, mixed with dry ice, and groiud in a Fitzpatrick Homoloid WD-36-3 hammer mill to pass a 500-micron screen 70-80 5 of the ground recycle was between 200-500 microns, the remainder finer. Twenty percent of recycle was mixed with 80 of the corresponding virgin formulation, and c ired the same way as before. When the recycled resin... 

In order to guarantee the suitability of the recyclate for direct food-con-tact or multilayer applications, in the presence of appropriate functional barriers, identification and quantification of low molecular weight contaminants in recycled resins becomes necessary. 

In recycled PP, 61 compounds were detected and 35 of them were identified. Many peaks showed very low separation levels making their identification difficult. In virgin and recycled PP the following compounds were identified Ethylbenzene and xylene were found only in the recycled resin. Present in both virgin and recycled PP were a large number of branched alkanes and n-alkanes between Qg and C25. Octadecanoic acid, methyl ester and dibutyl palmitate, which is a typical compound used in the cosmetic industry, were found only in the recycled PP. Amines such as hexamine, 3-ethyl and NIN"N" trimethyl dipropylene triamine were identified in both PP materials. Carboxylic acids and ketones were absent in both polymeric materials and so were fragrance or flavour compounds [113]. 

Once the plastic has been separated into its various types, it can be recycled by reprocessing. More commonly, some recycled polymer is added to virgin polymer, although this may limit the application of the resulting material. For example, poly(vinyl chloride) containing 25% recycled resin is available, but only for applications in which it does not come into contact with food. 

To efficiently use recycled plastics in molded parts, it is beneficial to work with several recycling suppliers to obtain a resin that is as close to the color of the product as possible. The resin that most closely matches the product may cost more per pound due to special sorting necessary to obtain a special color. This resin will probably cost less to use since it will require less corrective colorant to adjust the recycled resin to match the target. Recycled resins that are farther off color will require much more pigment to overpower the colorants in the recycled resin. 

Other properties that are important to the product or process include stress crack resistance, melt flow, and stiffness. Milk bottle resin has less stress crack resistance, higher flow, and slightly higher stiffness. If these properties would adversely affect the product/process, you should specify that you do not want significant quanities of milk bottle resin in the recycled resin. Other HDPE bottles are made from a lower density resin that has higher stress crack resistance and lower melt flow. 

Now that the colorant and recycled resin mix ratio have been determined in the laboratory, you are ready to evaluate the mix in a production machine. You need to mix a sufficient quantity of recycled resin with the appropriate amount of correcting colorant. Then try adding 10% of this mixture to the production material and mold parts. Measure the color of these parts, and if the color is acceptable, try using 20% of the recycled mix, and so on, until you reach the amount you want to use or the color becomes unacceptable. If the color is not acceptable at the desired percentage, add more production colorant to the mix. If you are molding multilayer parts, add more production colorant to the outer layer. It is much more efficient to add colorant to the outer layer whenever you have that option since the outer layer is normally made of 100% virgin and colorant. 

This process can achieve a recovery of scrap foam into a polyol mixture, which can be used to produce polyurethane without the need for purification. This method requires low capital investment and is simple enough to cope with variations in the mix scrap foam. The resulting recycled polyol can be incorporated with polyisocyanate to produce recycled polyurethane which can be used to modify recycled polyester mortar made with either virgin or recycled resins. 

Drying and reusing the same resin gives a modest 25% conversion, but after regeneration (LiAlH4 and oxidation with Pd(PPhj)4), the recycled resin gives an improved 79% yield. 

Standards requiring that certain products contain a minimum amount of recycled resin. 

Both positive and negative incentives, such as fees imposed on resins that do not meet the minimum standards for recycling or tax credits to businesses using recycled resins in their products. Likewise, in the case of feedstock recycling, many processes could be economically viable if a... 

The main constraints for improving mechanical recycling rates are the imbalance between the collectable waste and the potential end-markets for recycled resins, and the presence of large quantities of mixed plastic wastes which are difficult to clean and sort. 

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