Chemical Recycling of Reinforced Polyurethane From the Automotive Industry

M. MODEST1 and F. SIMIONI

University of Padova Chemical Process Engineering Department

35 1 3 1 Padova, Italy

R-RIM PU (reinforced-reaction injection molding polyurethanes) from the auto- motive industry (production scrap and parts at the end of their life cycle) can be recycled for the production of new RIM PU by a chemical process. Among the various possible chemical processes (hydrolysis, alcoholysis, aminolysis, and py- rolysis), we have examined glycolysis, a particular form of alcoholysis, for the purpose of obtaining a mixture of oligomers sufficiently similar to a polyol to be used in the production of new R-RIM PU. Glycolysis with dipropylene glycol (DPG) of R-RIM PU forms a monophasic product that could be used in the preparation of new, highly crosslinked polymers, similar to those used in the preparation of rigid thermal insulation foams. The same product, because of its high hydroxyi number, cannot be directly re-used in the production of new RIM PU. Partial substitution of free DPG in the glycolysis product with a trio1 having high molecular weight forms a homogeneous mixture suitable for production of new RIM PU. This final product has been used in the original R-RIM application introducing an appropriate opti- mization of formulation. In comparison with RIM PU obtained from only virgin materials, the loss in properties of molded parts based on even high amuunts of regenerated polyol was only marginal.

INTRODUCTION mesh). The powder can be directly used as a filler

IM and R-RIM (reinforced-reaction injection mold- R ing) polyurethane / polyurea polymers are materi- als that, owing to their intrinsic properties, are in- creasingly used in the automotive industry (bumpers, fascias, side panels, door interior panels, etc.). This kind of polymer contributes to improvements in safety, comfort, design, and, in particular, weight re- duction.

Disposal of scrap from production and waste from dismantling of cars at the end of their life is a problem that, because of present awareness of ecological as- pects by the public and also by politicians, requires solutions other than simple disposal.

Sending scrap to incineration with thermal recovery is a possible last stage operation for those materials that cannot be recovered in other ways. The energy content of these materials (28 to 32 MJ/kg) is actually only a fraction of the energy used in their preparation (1 ) .

Many studies are being carried out on processes for recycling. According to some authors (2-4). the re- grinding process involves, first, the granulation of scrap in a knife mill to a particle size of -3 mm and then its pulverization in an impact disc mill to a pow- der with a particle size of 180 to 300 pm (80 to 50

(-10%) in thermoplastics or in RIM PUS themselves. When adding the powder to polyethylene, one must use compatibilizers in order not to excessively de- crease its mechanical properties. For their utilization in RIM PUS, special technical modifications are nec- essary for dosing and mixing heads of the charging powder. The expensive investments involved, accord- ing to the same authors, do not produce sufficient returns.

Hot compression molding techniques are an alter- native approach. Scrap and waste, after being reduced to a granular size, are preheated to -160°C and placed in a mold at 175 to 185"C, where high-shear compression (30 to 80 MPa) produces a new thermo- formed part. This makes it possible for the recycled articles to be produced with 100% recycle content but not with good mechanical properties (i.e. poor resil- ience and elongation) (5).

In previous research, we have pointed out that gly- colysis processes represent a valid means for the eco- nomical recycling of scrap and waste from rigid foams (thermal insulating materials) (6). from microcellular elastomers (shoe soles) (71, from structural foams (wood substitute) (81, and from flexible polyurethane foams (automotive seating] (9). In this way, scrap and

21 73 POLYMER ENGINEERING AND SCIENCE, MID-SEmMBER 1- VOI. 36, NO. 17

M . Modesti and F. Simioni

Table 1. Bayflex 110 System (Urea-Urethane Polymer).

Functional Groups ( x l m

Parts by Mole/100g of Components Weight Polymer

A Polyether (eq. wt 1600)(a) 38.5 -OH 24 DETDA(~) 13.3 -NH, 149 Catalyst(c) 0.25 Milled fibers 16.3

B Modified MDl(a 31.65 -NCO 173 -NHCOO- 45

In the formulation, additives, such as internal mold release, are also present in unknown quantities.

Dipropylene glycol (DPG) used in the glycolysis was industrial grade (EniChem) with an H,O content of <O. 18% (Karl-Fischer). Diethyltoluene diamine (DETDA 80) was a product from Lonza Ltd with two isomers 2,4 and 2.6 and with a ratio of about 80/20.

Diphenylmethane diisocyanate (MDI-PR, EniChem) was used as received. Some materials such as solvents, cata- lyst, internal standards, etc.,. were bought from Aldxlch Chemical and used as received for specific analysis.

(’I Ethylene oxide tipped, hydroxyi No 35 rngKOH/g, trifunctional.

(’) Unknown. (q Diphenylrnethanediisocyanate rnodMed with tripropylene glycol (TPQ), -NCO: 23% (86.3% of MDi and 13.7% of TPQ).

Oiethyltoiuene diamine.

waste are transformed into a mixture of oligomers that can be used in the same production line as the original materials for the manufacture of new objects having properties similar to those obtained from pure polyol.

We therefore decided to examine R-RIM glycolysis to obtain a “polyol-like product” to be used in the pro- duction of new polyurethanes.

EXPERIMENTAL SECTION

Polymers and Reagents

The material used for the glycolysis was made of scraps from milled industrial R-RIM urethane-urea polymer, Bayer Corp.’s Bayflex 110, with 16.3% of milled fibers (10). The material was used as such with- out drying, as given in the Bayflex 110 formulation of Table 1. The matrix was formed of a mixed urea-ure- thane polymer with a theoretical molar ratio of 2.16.

G@!.o@is Conditions

When polyurethanes are treated with glycols at high temperatures (180 to 22OoC), several reactions lead to the dissolution of the polymer. The result depends on various factors such as

-type of glycol, -temperature, -type of catalyst, - glycol/polymer ratio.

DPG glycol was chosen for our tests because it makes possible the obtaining of single-phase oligomeric solu- tions. The temperature affects the reaction kinetics and the possible equilibria. From previous experience, a tem- perature of 2OOOC was chosen because it allows one to reach equilibrium in an acceptable time (3 h) with ap- propriate organometallic catalysts (1 1). It was also ob- served that, in the absence of catalytic materials, the time necessary to reach equilibrium becomes exces- sively long. Materials with catalytic effect described in the literature, particularly salts and hydroxides of alka- line metals and amines, promote decarboxylation. This

i” cs ”

52.49 FYg. 1. GPC of glycolysis products from polyurea/polyurethane RIM polymer. \

DPG ’16.87 -

21 74 POLYMER ENGINEERING AND SCIENCE, MID-SEPTEMBER 1996, VOI. 36, NO. 17

Chemical Recycling of Reinforced Polyurethane

decarboxylation is essentially llnked to the hydrolysis of the ureic and carbamic groups; the hydrolysis becomes more important in the presence of non-anhydritled gly- cols and nondried polymers.

The hydrolysis reactions can be represented by re- actions that lead to the evolution of C02 and to the formation of amines:

urethane group hydrolysis:

4-NH-CO-0-R'- + H2O * -@-NH2 + C02 + -R'-OH (1)

urea group hydrolysis:

-@-NH-CO-NH-@- + H2O * 2-@-NH2 + C02 (2)

where @ comes from isocyanate and R' from polyol. In the work mentioned above (1 11, it is also shown

that metallorganic compounds promote glycolysis but not hydrolysis, and therefore they behave as selective catalysts. Polyurethane glycolysis in the presence of organometallic catalysts has produced glycolysis ma- terials with a small amount of free amines.

R-RIM Olp-iS

In R-RIM PU obtained from the Bayflex 110 system (Table 1 ), there is a prevalence of ureic groups in the polymeric chain with a theoretical ratio of ureic car- bonyls to urethane carbonyls of 2.16. When these materials undergo glycolysis, a controlled degradation process takes place, in which the polymer is broken down to a mixture of liquid oligomers according to the following reactions: urethane groups glycolysis:

-@-NH-CO-0-R'-

+ HO-R"-OH * -@ -NH-CO-0-R-OH + -R'-OH

(3)

urea groups glycolysis:

with the conversion of the urea groups into urethane groups and the formation of amine groups. Owing to the symmetry of the diarylureas present in the poly- mer, glycolysis forms both the DETDA and DADPM (diamino diphenyl methane) amines. Glycolysis with DPG, as already pointed out, produces a mixture of low molecular weight products, terminated by active hydrogen groups that are all soluble in DPG.

A gel permeation chromatography analysis (GPC) of glycolysis reaction products obtained at 20O0C, after a 3-h reaction time, and with a DPG/R-RIM ratio = 1, is given in Ffg. 1. It shows the presence of ten compo- nents whose identification is reported in a previous work (1 2).

R-RIM glycolysis components are principally car- bamates and ureas with low molecular weight, which are soluble in an excess of DPG and in the polyether polyol derived from the original polymer. The milled glass fibers of R-RIM remain in suspension even after cooling of the reaction mixture. Some properties of the glycolysis products, obtained with two different R-RIM/DPG ratios, are given in Table 2.

The properties shown in Table 2 indicate that the products could possibly be used for the preparation of new, highly crosslinked polymers, similar to those used in the preparation of rigid foam thermal insula- tion. Rigid foams with valid properties have been pro- duced in laboratory tests carried out for this purpose ( 13). The presence of glass fibers does not allow these products to be used in normal industrlal plants for rigid foam production. Nowadays, several rigid-foam production companies, suitably equipped to work with filler, can already employ these products. The content of mffled fibers, however, is not a problem if the glycolysis product is used in R-RIM production plants.

R-RQ6-h RIM--

As reported in TabZe 2, reaction mixtures have a high hydroxyl number and therefore cannot be used

-@-NH2 + HO-RLO-f-NH-Q,'-

0

-@-NH-C-O-R=OH + -W-NH, II 0

-0-NH-C-NH-@'- + HO-R"OH II 0

SH3

80% 20% from DETDA isomers

from isocyanate

-R"- = from glycol

POLYMER ENGINEERING AND SCIENCE# MID-SEPTEMBER 1- Vol. No. 17 21 75

M. M o d e s t i and F. Simwnt

DPG (50) DPG (100) Ftg. 2. New glycolysis process A jlow sheet.

Table 2 Properties of R-RIM Glycolysis Products (After Hot Filtration of Milled Fibers).

R-RIMIDPG Ratio 0 1001150 100/100

GL YCOL YSZS ORGANOMETALLIC REACTOR CATALYST

Hydroxyl No (mg KOH/g) 550 475

DETDA (wt %)(*) 0.95 1.45

Viscosity (mPa - s 25°C) 21 65 3550 Total alkalinity (mg KOH/g) 33 42

DADPM (wt %)(* 0.91 1.58 DPG free (wt %)(@ 49.0 31.5

1’) Gas chromatographic analysis

Table 3. Reaction Parameters for the New Glycolysis Process.

Starting weight ratio R-RIM PU/DPG

Reaction time (h) 3 Reaction temperature (“C) 200 Weight ratio polymer/added virgin polyol 1:l Post reaction time during distillation of excess 2-4

Total reaction time (h) 5-7

1:l Glycol preheating temperature (“C) 180 .+ 200

glycol (150°C and 6.5 kPa) (h)

as such for the production of polymers with a suitable structure for RIM. The possibility of using such a mix- ture for this purpose, as a substitute for the original polyether polyol, depends on the possibility of obtain- ing a product with a lower hydroxyl number. This problem has been solved by partially substituting the free DPG in the glycolysis products with a high molec- ular weight triol having a lower hydroxyl number. Adding this triol also makes it possible to limit the viscosity increase caused by the distillation of excess free glycol.

Glycolysis runs were performed in a stirred reaction vessel (5-liter) equipped with a reflux condenser and kept at constant temperature by an oil bath. The

chopped RIM or R-RIM PU was transferred into the reaction vessel, which contained the preheated glycol (preferably dipropylene glycol) and catalyst, and vig- orously agitated. The rate of feeding was adjusted to the rate of dissolution. After 3 h of reaction, the low viscosity glycolysis product was mixed with a quantity of triol equal to the weight of the original R-RIM PU. The free DPG was partially removed by reduced pres- sure evaporation at 150°C.

The parameters used for the new glycolysis process are reported in Table 3, and the flow sheet of the process, with a mass balance, is shown in Fig. 2. It is not necessary for the new process to separate painted and unpainted polymer parts, or filled or unfilled parts. Products from PU formulations with internal mold release do not create problems.

Figure 3 reports a GPC chromatogram of a product obtained in this way. As can be seen from the chro- matogram, components of the product are the same as those found in the glycolysis of the RIM PU with DPG (Fig. 1 ) . The high molecular weight triol (-5000) does not interfere with the products and simply behaves as a solvent for a homogeneous system with a lower hy- droxyl number (there is no evidence of peaks with retention times lower than those of the triol).

Table 4 reports the main properties of the final product. As can be seen, the viscosity increase caused by the partial DPG substitution with the triol is lim- ited, while at the same time it is possible to obtain a remarkable decrease in the hydroxyl number and a low amine content.

Polyol mixtures from the new glycolysis process can be reused in the original R-RIM application. Up to 50 wt% of this recycled polyol (including triol for dilution) was added to fresh polyol without significantly affect- ing process parameters.

6 GJWVDER

R-RIM GROUND (100) 1 7

I f 4 I GLYCOL

DPG (SO) EVAPORATOR

t PRODUCT (250)

21 76 POLYMER ENGINEERING AND SCIENCE, MID-SEPTEMBER 1- Val. 36 No. 17

Fig. 3. GPC of-1 product for R- RIM PU recycling.

Chemical Recycling of Reinforced Polyurethane

r cs .' 13.83 I

Trio1 1

JZ .45

- - 69.35 79.76

Table 4. New R-RIM Glycolysis Product Properties (After Hot Filtration of Milled Fibers).

Hydroxyl No (mg KOWg) 215 Viscosity (mPa . s 25°C) 41 75 Total alkalinity (mg KOH/g) 40

DADPM (wt %)I@ 1.51 DPG (wt %)(* 5.1

DETDA (wt %)(@ 1.22

Table 5 shows an example of the properties and a comparison with properties of the original R-RIM poly- mer. The physical properties of specimens based even on high amounts of glycolysis polyol are very close to those of standard specimens. In particular, there is a reinforcement owing to the flexural modulus being slightly higher than the standard material (-20%) without a loss in flexibility. However, the HDT values are slightly lower. At any rate, these products show

Table 5. Properties of R-RIM Polymer Obtained With Glycolysis Polyols.

AStandard B C

Virgin polyol Glycolysis polyol

Density (kg/m3) Hardness (shore D) Elongation at break (%) Tensile strength (MPa) Flexural modulus (MPa) HDT value(@ ("C) Impact strength at -25"(C kJ/m2)

100 0

1270 68

163 29.0

1460 153 16

75 50 25 50

1285 1275 67.5 69

166 168 30.7 27.7

1620 1790 142 135 14.1 15.3

features that enable them to pass mechanical accep- tance tests required by the automotive industry.

CONCLUSIONS

The glycolysis process of R-RIM ureas/urethanes, reinforced with glass fibers has been examined in or- der to point out a method for chemical recycling, suit- able both for scrap and waste and for end-life materi- als (e.g. dismantling of end-life vehicles), as an alternative to physical recycling methods (hot com- pression molding, thermoforming, etc. I. The glycolysis process carries out a controlled degradation of the polymer, achieving liquid products at room tempera- ture, terminated by active hydrogen groups and capa- ble of reacting with isocyanate to obtain a new poly- mer. In particular, glycolysis of urea polymers leads to two kinds of amine compound, owing to group sym- metry, whose content in the final product is limited by the reaction of free amines with urethane groups (ami- nolysis equilibrium).

Glycolysis products, because of their properties, can be directly used in the production of new rigid foam insulating materials after preliminary elimina- tion of the milled glass fibers if suitable plants are not available.

From a technical and economical view, the employ- ment of products with reinforcement in new R-RIM PU production has proved more promising. For this pur- pose, a new glycolysis method leading to a product with properties near those of virgin materials has been found. The employment of this product in a pilot plant to obtain molded samples with valid properties has proved the feasibility of the process.

REFERENCES

1. G. F. Baumann, W. J. Farrissey, and J. I. Myers, Poly- urethane World Congress, p. 335, Nice, France (1991).

POLYMER ENGINEERING AND SCIENCE, MID-SEPTEMBER 1- Vol. 36, No. 17 2177

M . Modest i and F. Simtont

2. R. E. Morgan, G. H. Dean, R. L. Tabor, and M. Zawisza, Polyurethane World Congress, p. 653, Nice, France (1991).

3. R. E. Morgan, L. B. Weaver, and M. Munstermann, Poly- urethane World Congress, p. 120, Nice, France (1991).

4. W. J. Farrissey, R. E. Morgan, R. L. Tabor, and M. Zaw- isza, in Emerging Technologbs in Plastics Recycling. G . D. Andrews and P. M. Subramanian, eds., Washington, D.C. (1992).

5. B. Meister and H. Schaper, Kumtstoge German Plastic, 80. 13 (1990).

6. F. Simioni. S. Bisello. and M. Tavan, Cellular Polym., 2, 281 (1983).

7. M. Modesti. S. A. Rienzi. and F. Simioni, in Advances in the Chemistry and Processing of Various Elastomers. vol. 1. M. A. Kohudic, ed., Technomic Publishing, Lancaster, Pa. (1994).

8. F. Simioni. M. Modesti, and S. A. Rienzi, Macplas Inter- national, 107 (August 1990).

9. F. Simioni and M. Modesti, Cellular Polym., 12, 337 (1993).

10. H. J. Mainers, H. Boden, andH. J. Braun, Polyurethane World Congress, p. 883, Nice, France (1991).

11. M. Modesti, F. Simioni, and S. A. Rienzi, Cellular Poly- mers, International Conference, London (March 199 1).

12. F. Simioni. M. Modesti, and S. A. Rienzi, Cellular Poly- mers. 2nd International Conference, Edinburgh, U.K. (March 1993).

13. F. Simioni, M. Modesti, andS. A. Rienzi, Macplas, 151, 121 (1993).

Received September 1 1 , 1995 Revision received February 21, 1996

21 78 POLYMER ENQINEERING AND SCIENCE, MID-SEPTEMBER 199e, WOI. 36, NO. 17