Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Process of treating scrap or waste product containing solid...
Reexamination Certificate
1999-05-26
2002-01-01
Cain, Edward J. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Process of treating scrap or waste product containing solid...
C521S040000
Reexamination Certificate
active
06335376
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to the separation and purification of plastics.
BACKGROUND
The production of plastics accounts for over $40 billion of annual product sales and more than 3% of the United States consumption of oil and natural gas. More than 90% of our production of these valuable materials is discarded. This is a considerable waste of natural resources and imposes an unwanted growing burden on people, cities, regions, agencies concerned with management and conservation of resources and pollution, and of course, ultimately on the environment. Improved collection, separation and reuse of plastics would tend to alleviate worsening of these burdens. If the collection, separation and reuse of plastics were sufficiently improved, plastics recycling could become one of the largest raw materials industries worldwide within a decade.
By generating over 80 billion pounds of material or $270 billion of production per year, and being responsible for approximately 3.2 million jobs, plastics and related businesses represent an extremely important materials industry to the United States. Unlike other material industries like steel and aluminum, however, this industry depends almost solely on new sources of raw material, most of it imported petroleum. This dependence becomes even more significant as the growth rate of plastics continues to outpace that of all other materials. Wasting this important material resource has significant international trade, economic and environmental implications.
The US produces almost 20 billion pounds per year of valuable engineering plastics for use in durable goods. These products are increasingly being collected and recycled at the end of their useful lives to avoid disposal costs and potential liabilities, and to recover metals and other marketable raw materials. The engineering plastics contained in these products are often one of the most valuable materials on a cost per pound basis, yet most of this valuable plastic resource is therefore landfilled, incinerated, or sent to Asia for recycling and reuse there.
Examples of the plastics recycling problem are evident in the case of so called ‘disposable’ plastic bottles and in durable goods. The main barrier to the recycling of a majority of bottles is that separation is limited to density-based systems which require significant pre-sorting by plastic type at Material Recovery Facilities (MRFs), leading to insufficient feedstock supply and poor economics. The main barrier to recycling of plastics from durable goods, such as automobiles, appliances, and computer and electronic equipment, is the multitude of plastic types and with different grades of the same type of plastic, often with overlapping densities, which must be separated. The re-use of such plastics, even if they can be separated, is often complicated by their degree of contamination, e.g. paint, metal film coatings and the like.
SUMMARY
Embodiments may include one or more of the following advantages. The inventions enable the plastics to be separated from complex mixtures and recycled with high purities that result in higher market values. The recycling concept is certainly not new to plastics. Plastics have been recycled and reused since the beginning of their commercial use. Scrap and uncontaminated rejected parts generated from a manufacturing process are shredded and reused, typically back into the same application. As with other types of materials such as metal and glass, different types of plastics must generally be separated from one another to achieve high purity and consistent extruding or molding performance i.e., consistent physical properties typically verified by standardized ASTM tests (Izod impact, Deflection Test Under load (DTUL). Melt Flow Index (MFI) and the like) and higher market values.
Plastic types include acrylonitrile-butadiene-styrene (ABS), flame retardant (FR) ABS, ignition resistant (IR) ABS, acrylonitrile-styrene-acrylonitrile (ASA), high density polyethylene (HDPE), high impact polystyrene (HIPS), FR HIPS (a flame retardant HIPS), IR HIPS (an ignition resistant HIPS), low density polyethylene (LDPE), polyamide (PA), polybutylene terephthalate (PBT), polycarbonate (PC), PC/PBT (a blend of PC and PBT), PC/ABS (a blend of PC and ABS), FR PC/ABS (a FR blend of PC and ABS), polyethylene (PE), polyethylene terephthalate (PET), polymethyl methacrylate (PMMA), polyoxymethylene (POM), polypropylene (PP), polyphenylene oxide (PPO), polystyrene (PS), polyvinyl chloride (PVC), PVC/ABS (a blend of PVC and ABS), styrene acrylonitrile (SAN), styrene-butadiene rubber (SBR), styrene maleic anhydride (SMA), thermoplastic polyolefin (TPO), thermoplastic polyurethane (TPU), thermoplastic elastomer (TPE). Most plastics of different types are not compatible with one another, and while some commingled applications have been demonstrated, they capture much lower values than virgin plastic because the significant physical properties and characteristics are much less controlled, if at all, i.e. the plastics are of lower grade. With lower grade or lower purity products, the processing and performance flexibility afforded by purified single resin streams or compounded resin combinations (co-polymers) of consistent characteristics is lost.
As important, perhaps, is the ability to separate different grades of the same type (i.e., polymers built from the same monomer or monomers, but of different molecular weight, different ratios of monomers, different molecular morphology, different additive composition, concentration and the like) of plastic. Different plastic grades (i.e. plastics of the same type with a different range of properties) can have significant differences in important physical properties: e.g., medium impact, low gloss ABS and high-heat ABS.
Although an increasing number of bottles and rigid containers of all types are being recycled, a significant improvement in collection and reprocessing economics is needed for a majority of bottles to be recycled. Other types of plastics packaging (film, coatings, and closures) are recycled at a considerably lower rate than bottles. Durable goods (e.g. buildings, automobiles, appliances, and computer and electronic equipment) are gaining attention as a recycling opportunity as these types of products are increasingly being collected at the end of their useful lives by recyclers and manufacturers who recover useable components and metals. Although more plastic is actually used in durable goods than in packaging, technical barriers preclude their economical separation from these mixed material streams using conventional methods.
The problem of separating different polymeric materials from each other is the primary obstacle to economically recycling polymeric materials from durable goods, particularly when they have similar or overlapping density distributions. Durable goods are generally formed from a number of different types and grades of polymeric articles arranged as separate component sub-structures (pieces or parts) combined or attached into a unitary item, e.g., a computer monitor with a case of one material having several other sub-assemblies attached by glue, molding, or fasteners and the like.
Most plastic parts coming from durable goods streams contain unique challenges that are not met by the automated conventional plastics cleaning and sorting processes developed for packaging materials. The principle practice today for the recovery of highly contaminated scrap is hand-separation, which is cost prohibitive in most cases. The challenges in recycling plastics from durable goods include:
The plastics used in durable goods are more specialized than those used in packaging. Whereas the majority of plastic packaging can be categorized in five grades of plastic resin, more than fifty plastic resin grades might be required to comprise a similar fraction of the durables market. For example, while the PET plastic used to make a soda bottle may also be appropriate for a water bottle, the acrylonitrile-butadiene-styrene copolymer (ABS) used to make a computer housing
Allen, III Laurence E.
Arola Darren F.
Cain Edward J.
Fish & Richardson P.C.
MBA Polymers, Inc.
Wyrozebski-Lee Katarzyna
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