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Recycling Of Polyurethane Foam WastesRONAK VAGHANI: 11POL1006

GUIDE: DR. ANAGHA S. SABNIS

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What are PU foams?

PU Foams

Polyol

Isocyanate

CatalystsBlowing Agents

Surfactants*

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Where are they used?Rigid PU foams:

◦ Refrigeration◦ Thermoware like Casserole◦ Industrial Insulation

Flexible PU foams:◦ Automotive Car Seating◦ Foam Mattresses, Pillows

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Why do they need to be recycled?

Global Consumption of 17.5 Million MT of Polyurethane.

Waste Disposal Non Bio-Degradable. Adverse Effects like

Flammability. Effect of Blowing agents

on the environment.

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How can we recycle them? Methods of Recycling:

Mechanical Chemical

Thermo-Chemical Biological

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Physical/Mechanical Methods Grinding

Used as filler in new PU foam Average particle size is 50 μm Recycle content of 7-10 %-wt.in the new

foam Cost savings of around 2.7-2.8 %

Toyota made mudguard by addition of 10% wt. powder (Reduction of 4-5% cost)

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Mechanical Methods…Adhesive Pressing.

Scrap PU particles are surface coated with a binder and bonded in a heated press.

Production of mats, carpet underlay, sports hall floor parts and automotive sound insulation.

PU foam scrap can be rebonded by mixing scrap particles (size ~1 cm) with di-isocyanate MDI followed by form-shaping at 100-200°C, 30-200 bar

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Mechanical Methods… Compression/Injection MoldingMolding at temperatures and

pressures high (180°C, 350 bar) enough to generate the shear forces needed to flow the particles together, without the need for additional binders.

SRIM (structural reaction injection molding)

Mainly used in Automotive parts.I.M. carried out for crosslinked PU.

( with addition of thermoplastics)

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Chemical Methods…Glycolysis:The purpose is to recover the polyol.

In the process, three phases are obtained: an upper phase which contains the polyol a bottom phase which has the sub products of the reaction and the excess of glycola third phase which is in the middle and it is formed by the polyurethane unreacted.

Choosing the right reagent and degradation condition can get high quality polyol, not only with low reaction temperature and short reaction time, but also with higher degradation efficiency

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Chemical Methods…Glycolysis

T=180-220⁰C

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Chemical Methods…Conventionally catalysts used areAmines [DEA (Diethanolamine)] Alkoxides (Titanium n-butoxide)Hydroxides( NaOH)

Polyols are used as a solvent system(DEG)

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Advances in GlycolysisMicrowave Assisted Glycolysis: pentaerythritol with (glycerine+ NaOH)

Scraps of flexible PU foam with above ingredients was put it in microwave oven at180⁰C and 800W.

Split phases appeared after complete foam digestion. The upper phase contained recycled polyol, and the lower phase was a brown liquid with highly functionalized oligomers, amines and unreacted degradation reagents and showed potential for application in rigid polyurethane foam formulation.

Easy to process, rapid, eco-friendly and amine-free polyol was achieved in high yields and purity.

New CatalystsPotassium and calcium octoatesThey lead to the complete degradation of the polymeric chain at low reaction time and the recovery of

the polyol in high concentration.Main advantage: amount of octoate used represents only 15% by weight of the DEA needed.Low cost of octoates.

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Chemical Methods…Hydrolysis:Under the action of water vapour in 250-340°C, polyurethane is degraded into diamine, polyol and CO2 in high pressure.

Catalyst used is an alkali metal hydroxide.

Initially, Superheated steam @200⁰C was used, takes 15mins to obtain Volume Reduction factor of 30.

Now, We use superheated steam@288 ⁰C with 5% virgin material to obtain excellent polyol.

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Chemical Methods…Amine Method:Researcher Xue degraded the rigid polyurethane foams with fatty amine (such as diethylenetriamine, triethylenetetramine). The main reaction included the fracture of carbamate base, urea base, biuret base and urea base formic acid ester base, and the generation of polyol, multiple amine and aromatic compounds in the degradation process.Reaction can happen at low temperature.

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Chemical Methods…Phosphate Ester MethodDegradation reaction can happen in 142 °C without catalyst. Troev K. speculated that alkylation reaction, free radical reaction and ester exchange reaction happened between polyurethane and phosphate

Also used are phosphoric acid ethyl ester, triethyl phosphate, chlorine ethyl triethyl phosphate, which degraded the microporous polyurethane elastomer at 180 °C, the degradation product was liquid, containing phosphorus element or phosphorus and chlorine element oligomer

These products can be used as non-reactive additives to improve the flame retardant performance

Only used in packing, applications need further study.

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Thermochemical Methods

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Thermochemical Methods…PyrolysisPyrolysis of a PU foam was analysed using TGA up to 450°C (in nitrogen, 5-20 K/min heat-up) and a “pyroprobe” pyrolysis reactor at 500 - 800°C (in nitrogen, heat-up ~300 K/s) plus a secondary reactor .

Decomposition of the PU to a mass loss of~95% occurred between 230 and 380°C.

The tests in the “pyroprobe” set-up yielded gas mixtures containing at 500°C large fractions of toluene, benzene, methyl 1,4-pentadiene, ethane +ethylene, propylene and butadiene, at 900°C mainly benzene, ethane + ethylene, and methane.

Also, ammonia (NH3), pentene and the semi-volatiles 5-hexen-1-ol and 1, 6-hexane diol were found in significant amounts in the products, as also some hydrogen cyanide (HCN), aniline (aminobenzene), benzonitrile and naphthalene, at levels depending on temperature.

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Thermochemical Methods… Gives syn gas. Takes place in oxygen

@1200-1500⁰C, 20-80 bar. Residence time of few

seconds gives 98-99% conversion.

Benefit :chlorine (from CFCs) is bound by the ammonia formed (from PU nitrogen) to form ammonium chloride (NH4Cl).

Gasification

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Biological DegradationMicrobial degradation of polyurethanes is dependent on the many properties of the polymer such as molecular orientation, crystallinity, cross-linking and chemical groups present in the molecular chains which determine the accessibility to degrading-enzyme systems

Involves 2 classes of enzymes belonging to the esterase and protease families.(both membrane-bound and extracellular)

Microbial degradation of polyester polyurethane is hypothesized to be mainly due to the hydrolysis of ester bonds by these esterase enzymes.

Enzymes: human neutrophil elastase and porcine pancreatic elastase.

Bacteria: Delftia acidovorans TB-35 (Polyester), Staphylococcus epidermidis(Polyether)

Fungi: Aspergillus terreus (Polyester), Chaetomium globosum( Polyether).

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Other MethodsPrevent the release of CFC into the atmosphere.During shredding, the CFCs released must be trapped, after which they can be destroyed.The extraction of blowing agents CFC-11 and HCFC-141b from rigid PU foams using supercritical CO2 (sc-CO2) can be done due to very high diffusivity of the sc-CO2 through the polymer.Extraction efficiencies

>99% -sc-CO2 and (slightly less efficient) sc-CO2/C3H8 mixtures, shorter time.40% with liquid CO2 and 14% removal with N2 , longer time.

The extracted gases are then trapped and the PU can be stored for further processing.

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ConclusionMethods conserving cost and energy have to be found Large Scale Processing should be feasible.More R&D in Biopolymers and suitable replacement of PU is much needed.The existing methods are capable of a high yield but that is not observed on an industrial scale.Innovative methods need to publicized well for world wide PU Industries.Market for recycled products has to be established. It doesn’t end at recycling, but optimum use of the end product of recycling has to be carried out.

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Thank You