Material recycling of RIM-polyurethanes.There is a choice of different methods to recycle RIM (reaction injection molding Reaction injection molding OR RIM Molding is similar to injection molding except that a reaction occurs within the mold. The process uses thermoset polymers (commonly polyurethane) instead of thermoplastic polymers used in standard injection molding. ) polyurethanes polyurethanes (pŏl'ēyr`əthānz), group of plastics that may be either thermosetting or thermoplastic. Polyurethane can be made into both flexible and rigid foams. . Rim-polyurethanes can be subjected to chemolytic processing methods (ref. 1) and become thus transferred into polyols and polyol/amine mixtures. Small amounts of these regenerates can be added to virgin material and reused for original applications. The mechanical properties of articles produced in this manner are somewhat reduced. Another alternative is the use of ground RIM-polyurethanes as a filler in RIM-parts (ref. 2) or thermoplastics such as polypropylene polypropylene (pŏl'ēprō`pəlēn), plastic noted for its light weight, being less dense than water; it is a polymer of propylene. It resists moisture, oils, and solvents. (ref. 2). Because of the crosslinked and duroplastic character of RIM-polyurethanes a true material recycling which has been realized in the public mind only for thermoplastics was thought to be impossible. It will be shown to you now that on the contrary, because of the crosslinked and duroplastic network of RIM-polyurethanes with physical and chemical bondings, material recycling is possible. Our new technology allows 100% reuse of recycled material (ref. 3).
Under heat and pressure crosslinked RIM polyurethanes can be reshaped. This thermoforming procedure is similar to the deep drawing of sheet steel for carpet panels. Figure 1 shows the result of this deep drawing of a RIM plaque. As can be seen from the deformation deformation /de·for·ma·tion/ (de?for-ma´shun)
1. in dysmorphology, a type of structural defect characterized by the abnormal form or position of a body part, caused by a nondisruptive mechanical force.
2. of the equidistant e·qui·dis·tant
equi·distance n. line pattern, there is material flow from areas, which are not directly exposed to heat and pressure into the cavity. No melting of the material takes place at all.
How does the process work?
Elastomeric RIM-polyurethanes comprise hard and soft segments which are arranged in cluster or domains. The stiffness of the hard segments results from physical bonding (hydrogen bonding hydrogen bonding
Interaction involving a hydrogen atom located between a pair of other atoms having a high affinity for electrons; such a bond is weaker than an ionic bond or covalent bond but stronger than van der Waals forces. ) which are thermally reversible (ref. 4). Three functional polyether pol·y·e·ther
A polymer in which the repeating unit contains two carbon atoms linked by an oxygen atom. polyols or polyamines crosslink the soft segments. These crosslinkages are thermally not reversible and do not split under the processing conditions of this procedure.
Figures 2-4 show the schematic network of RIM-polyurethanes. Thermoforming of RIM-polyurethanes leads to new parts of stable geometry. The material does not pass a liquid stage during pressing. At the process temperature the physical (and some chemical) bondings in the hard segment domains open. The mechanism corresponds to a certain extent to the melting of thermoplastic A polymer material that turns to liquid when heated and becomes solid when cooled. There are more than 40 types of thermoplastics, including acrylic, polypropylene, polycarbonate and polyethylene. polyurethanes. However in contrast to TPUs the chemical crosslinkages in the soft segments inhibit real melting. This performance excludes the options of conventional thermoplastic processing technologies. The soft segments form a matrix which allows orientation and reconfiguration of the "molten" hard segment domains. At cooling the hard segment domains crystallize crys·tal·lize also crys·tal·ize
v. crys·tal·lized also crys·tal·ized, crys·tal·liz·ing also crys·tal·iz·ing, crys·tal·liz·es also crys·tal·iz·es
1. again and thus stabilize the new geometry (see table 1).
Table 1 - conditions for deep drawing of Bayflex 110/80 semifinished goods Preheating time 0.2 - 15 min. Preheating temperature 140 - 1800C Mold temperature 180 - 1900C Mold residence time 1 - 5 min. Specific pressure 1 - 400 bar Demolding temperature 180 - 190'C
Plaques of RIM and RRIM RRIM Reinforced Reaction Injection Molding polyurethanes which have thinner cross sections can also be deep drawn by vacuum and heat.
Deep drawing of RIM and RRIM-polyurethanes leads to articles of new design with 100% recovery of properties. Sometimes the property profile is even improved provided specific processing conditions are strictly observed. This will be explained by figures 5 and 6.
A sensitive physical property: Dimensional stability dimensional stability,
n See stability, dimensional.
A very important property of the demolded article is their dimensional stability. The following figures demonstrate the dependence of shrinkage on various press temperatures, varying hard segment content (see figure 7) and the degree of crosslinking in the hard segment, respectively (see figure 8). The thickness of the samples is measured. The shrinkage is observed as increase in cross section.
Figure 7 demonstrates the shrinkage of the Bayflex 110 series. Practically no shrinkage is observed at mold temperatures above 150 [degrees] C, whereas between 130 [degrees] C and 150 [degrees] C it depends on the Detda content.
In the range of 140-160 [degrees] C shrinkage goes up at higher crosslinking density (figure 8) in the hard segment which was achieved by increasing the functionality of the isocyanates. Above 170 [degrees] C shrinkage does not occur anymore, below 170 [degrees] C shrinkage depends on the degree of chemical crosslinkage.
These investigations suggest that the physical bondings rearrange re·ar·range
tr.v. re·ar·ranged, re·ar·rang·ing, re·ar·rang·es
To change the arrangement of.
re at temperatures between 160 [degrees] C and 170 [degrees] C. Thermoformed parts which are produced over 170 [degrees] C do not reveal frozen-in tensions. That means there is no stress on the polymer matrix.
In morphology and thermo-mechanical properties the articles correspond to post-cured RIM parts which are characterized by full relaxation of any tensions.
At temperatures above 170 [degrees] C no shrinkage is observed any more independently from the network's structure. This is because the physical network is complete and the chemical network is partially resolved.
The region between approx. 140-170 [degrees] C dominates the influence of the nature of the chemical network while the physical network is already resolved. Changes in the branching of the hard segment therefore have a significant influence on the shrinkage. Under 140 [degrees] C the physical network also remains intact and is influenced by the nature of both networks. Shrinkage is dominated mostly by its hard segment content. This shows the strong influence of the physical network at these temperatures.
So two mechanisms which control and stabilize the geometry of articles are under discussion. In addition to the physical factors, which are always active at temperatures above 160-170 [degrees] C splitting and reformation of chemical bondings can be observed (see figure 9).
Compression molding Compression molding is a method of molding in which the molding material, generally preheated, is first placed in an open, heated mold cavity. The mold is closed with a top force or plug member, pressure is applied to force the material into contact with all mold areas, and heat of granul9es
The interaction of physical and chemical factors permits the production of new articles form granules Granules
Small packets of reactive chemicals stored within cells.
Mentioned in: Allergic Rhinitis, Allergies of RIM-polyurethanes. We call this procedure compression molding. The process is based on production waste or used parts which are chopped to a screen size of 2-3 mm on an appropriate cutting device. Granulating is done at ambient temperatures Outside temperature at any given altitude, preferably expressed in degrees centigrade. . No brittlening of the material by cooling to low temperature is necessary. For the molding process the granule granule, in astronomy: see photosphere. is preheated in an oven and transferred into a steel tool with shear edges (see table 2). Its pronounced flowability allows undercuts and extended vertical areas in the tool.
Table 2 - table of typical compression molding conditions Grain size (screen size) 2 - 3 mm Preheating time 1 - 12 min. Preheating temperature 140 - 150 [degrees] C Mold temperature 180 - 190 [degrees] C Mold residence time 1 - 3 min. Specific mold pressure [is greater than or equal to] 350 bar Demolding temperature 180 - 190 [degrees] C
The recombination recombination, process of "shuffling" of genes by which new combinations can be generated. In recombination through sexual reproduction, the offspring's complete set of genes differs from that of either parent, being rather a combination of genes from both parents. and extent of unification of the granule grains is mainly responsible for property conservation of compression molded articles. Obtained property maintenance depends on the same conditions as deep drawing, especially pressure, preheating and mold temperatures. Mold residence time and mold temperatures also influence the surface roughness of new moldings.
The properties are also influenced by tool geometry, granule distribution and positioning in the tool (table 3).
[TABULAR DATA OMITTED]
All properties which depend on the orientation of the fibrous fibrous /fi·brous/ (fi´brus) composed of or containing fibers.
Composed of or characterized by fibroblasts, fibrils, or connective tissue fibers. filler are averaged, which is the reason for the reduced flexural flexural
pertaining to the flexure of a joint.
fixation of joints in flexion. In the newborn called contracted calves or foals. elasticity modulus.
Optimization of properties
By compression molding of a specific RIM material the properties can be recovered to a certain extent. With a given Bayflex 110 composition only minor property improvements can be achieved by further optimizing the conditions of compression molding. The level of physical properties of recycled materials is also dependent on the chemical composition of the Bayflex RIM systems. All components were varied separately. Also interactions between the components were considered. The objective was to maintain 100% properties after compression molding. The results are shown in table 4.
[TABULAR DATA OMITTED]
Compression molding technology provides a superb procedure to generate recycling articles from RIM-polyurethanes granules. It applies a well known technique and produces 100% recycled articles of three dimensional geometry. The property profile is well balanced. It can be further improved by using RIM systems which are optimized for recycling purposes. First commercial utilization is expected in the automotive industry The automotive industry is the industry involved in the design, development, manufacture, marketing, and sale of motor vehicles. In 2006, more than 69 million motor vehicles, including cars and commercial vehicles were produced worldwide. this year.
References [1.] Bayer, G. 1991. Kunststoffe, 81:301 and therein cited literature. [2.] Meister, B. and H. Schaper. 1990. Kunststoffe, 80:1260. [3.] Ep's 310,896, 334,171, 348,760, 366,925, 371,330, Bayerag. [4.] Dieterich, D. 1983. Kunststoff-handbuch, vol. 7; G. Oertel, Carl Hanser Verlag, ed Polyurethane polyurethane
Any of a class of very versatile polymers that are made into flexible and rigid foams, fibres, elastomers (elastic polymers), surface coatings, and adhesives. , Munchen, Wein, p. 3]f and therein cited literature.