**From PET Waste to Novel Polyurethanes**

Gity Mir Mohamad Sadeghi and Mahsa Sayaf

*Dep. Polymer Engineering & Color Technology, Amirkabir University of Technology, Tehran, I.R. Iran* 

#### **1. Introduction**

356 Material Recycling – Trends and Perspectives

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and recovery of phosphorus from steelmaking slags with the aid of a strong magnetic field. *ISIJ international*,Vol.47, No.10,(2007), pp.(1541-1548), ISSN0915-1559 It is well known that Poly (ethylene terephthalate) (PET) is a semi-crystalline thermoplastic polyester widely used in the manufacture of apparel fibers, disposable soft-drink bottles, photographic films, etc. The world production of PET in 2002 was 26 million tons which is expected to rise to 58 million ton in 2012 (Kloss J et al, 2006 & Shukla SR, 2009). The majority of the world's PET production is for synthetic fibers (in excess of 60%) with bottle production accounting for around 30% of global demand. The polyester industry makes up about 18% of world polymer production and is third after polyethylene (PE) and polypropylene (PP). Large numbers of post-consumer PET products, especially bottles and containers, do not create a direct hazard to the environment, but are being concerned due to their substantial volume fraction in the solid waste streams, their high resistance to the atmosphere, their poor biodegradability and photo degradability. Recently, recycling of PET has received a great deal of attention. Although the nontoxic nature, durability and crystal clear transparency of PET during use are major advantages, its non biodegradability is the serious cause of concern to the environmentalists. Since land filling of such non biodegradable waste has severe limitations, chemical recycling is the best possible alternative. Therefore, chemical recycling of PET leads to various advantages: consuming waste to get new useful materials and changing of a non- biodegradable polymer to a biodegradable one. Chemical recycling of PET includes chemolysis of the polyester with an excess of reactants such as water (hydrolysis) (Pusztaszeri SF, 1982, Mishra S et al, 2003; Schwartz J, 1995; Lamparter RA et al, 1985; Tindall GW et al, 1991 & Doerr ML, 1986) alcohols (alcoholysis), glycols (glycolysis) (Akiharu F et al,1986; Ostrowski HS,1975; . Güçlü G et al, 1998, Andrej K, 1998; Berti C et al, 2004; Manfred K et al,1993), amines (aminolysis) (Shukla SR et al,2006 ; Fabrycy E et al,2000;Zahn H et al,1963; Popoola V,1998) and ammonia (ammonolysis) (Blackmon KP et al,1990). Aminolysis has been little explored as chemical degradation of PET for synthesis of useful products. The use of ethanolamine for aminolytic degradation of PET waste has been investigated. (Shukla SR et al, 2006) The product obtained BHETA has potential for further reactions to synthesize useful products such as polyurethanes. There are few reports on the usage of recycled BHETA from PET to synthesis of polyurethanes. Depolymerization of the PET waste, using ethanolamine to obtain BHETA and BHETA-based polyurethanes, has been investigated in our works (Shamsi R et al, 2009; Mohammadi M et al, 2010; Mir Mohamad Sadeghi G et al, 2011). This

From PET Waste to Novel Polyurethanes 359

which is expected to rise to 55 million ton in 2010. PET resin, or bottle grade, is one of the fastest growing plastics markets. Polyester fiber is the second largest segment, but the market is mature. The third use, film, is also a mature market, for example PET market in

Fig. 2. PET market in USA in 2008(chemsysytem.com,nexant ,PERP 07/08-5:1-8).

12% by volume of the world's solid waste (Shamsi R et al, 2009).

for paper, glass and metals are, respectively, 34%, 22% and 30%.

and chemical recycling have been developed.

bottle can conserve enough energy to light a 60 W light bulb for up to 6 h.

Large numbers of Post-consumer PET products especially bottles and containers do not create a direct hazard to the environment, but as a problem due to its substantial volume fraction in the solid waste streams, its high resistance to the atmosphere, its poor biodegradability and photo degradability. PET accounts for more than 8% by weight and

An estimated billion plastic bottles are disposed of each year, while recycling a single plastic

Recently, recycling of PET has received a great deal of attention and many attempts are currently directed toward recycling of post-consumer PET products because of both environmental protection and economic benefits. Also necessity for recycling of this product is felt more (Fig 3). In Singapore, 684,400 tones of plastic waste were generated in 2008 and the recycling rate was 9%. Although the nontoxic nature, durability and crystal clear transparency of PET during use are major advantages, its non biodegradability is the serious cause of concern to the environmentalists. Because it isn't appropriate to dispose of waste PET by land-filling, alternative methods of recycling of waste PET products include physical

To minimize the fast buildup of PET waste, different mechanical, thermal, and chemical methods to separate, recover and recycle PET from post-consumer waste stream have been used (Mohammadi M et al, 2010). Products made from recycled PET bottles include carpeting, concrete, insulation and automobile parts. Recycled PET bottles are also used in drainage filtration systems, asphalt concrete-mixes and road stabilizations. Recycling rate of such polymer products is however still low comparing to that of paper, glass and metals. Currently only 3.5% of generated polymeric products is recycled whereas these percentages

Physical recycling of PET consists of the collection, separation, digestion, granulation of polymer waste and then recirculation into production. Blending of materials with PET waste

USA in 2008 could be shown in Fig.2.

chapter aims at the study on synthesis of novel polyurethanes based on PET waste. Firstly, PET and polyurethanes are concisely reviewed, with emphasis on the methods of synthesis, their structures, properties and applications. Then, various chemical decomposition methods of PET are introduced. Using aminolysis in the presence of Ethanolamine, applying of aminolysis product (BHETA) as chain extender or ring opening agent to obtain new polyurethanes are demonstrated. Mechanical, thermal properties, biodegradability, chemical resistance, adhesion of novel synthesized materials are studied. Thirdly, effective parameters such as structural hard segment, chain length, chemical structure, and crystallinity on final properties as well as biodegradability are investigated.

### **2. Poly (ethylene terephthalate)**

Poly (ethylene terephthalate) is a thermoplastic polymer resin of the polyester family and is used in synthetic fibers; beverage, food and other liquid containers; thermoforming applications; and engineering resins often in combination with glass fiber. Depending on its processing and thermal history, polyethylene terephthalate may exist both as an amorphous (transparent) and as a semi-crystalline polymer. The semicrystalline material might appear transparent (particle size < 500 nm) or opaque and white (particle size up to a few microns) depending on its crystal structure and particle size. Its monomer , BHET can be synthesized by the esterification reaction between terephthalic acid and ethylene glycol with water as a byproduct, or by transesterification reaction between ethylene glycol and dimethyl terephthalate with methanol as a byproduct (Fig. 1-a). Polymerization is through a polycondensation reaction of the monomers (done immediately after esterification/ transesterification) with water as the byproduct (Fig.1-b).

Fig. 1. b. Polycondensation of BHET yields PET.

#### **3. PET waste, as an opportunity instead of a problem**

PET is used in the preparation of a variety of products differing widely in their physical characteristics and hence, their end uses. The varieties of prominence are fibers and filaments, sheets and disposable soft-drink, soda drinks, juice, mineral water, soy sauce bottles, photographic films, etc. The world production of PET in 2002 was 26 million tons

chapter aims at the study on synthesis of novel polyurethanes based on PET waste. Firstly, PET and polyurethanes are concisely reviewed, with emphasis on the methods of synthesis, their structures, properties and applications. Then, various chemical decomposition methods of PET are introduced. Using aminolysis in the presence of Ethanolamine, applying of aminolysis product (BHETA) as chain extender or ring opening agent to obtain new polyurethanes are demonstrated. Mechanical, thermal properties, biodegradability, chemical resistance, adhesion of novel synthesized materials are studied. Thirdly, effective parameters such as structural hard segment, chain length, chemical structure, and

Poly (ethylene terephthalate) is a thermoplastic polymer resin of the polyester family and is used in synthetic fibers; beverage, food and other liquid containers; thermoforming applications; and engineering resins often in combination with glass fiber. Depending on its processing and thermal history, polyethylene terephthalate may exist both as an amorphous (transparent) and as a semi-crystalline polymer. The semicrystalline material might appear transparent (particle size < 500 nm) or opaque and white (particle size up to a few microns) depending on its crystal structure and particle size. Its monomer , BHET can be synthesized by the esterification reaction between terephthalic acid and ethylene glycol with water as a byproduct, or by transesterification reaction between ethylene glycol and dimethyl terephthalate with methanol as a byproduct (Fig. 1-a). Polymerization is through a polycondensation reaction of the monomers (done immediately after esterification/

Fig. 1. a. Chemical Reaction between ethylene glycol and terephthalic acid yields BHET.

PET is used in the preparation of a variety of products differing widely in their physical characteristics and hence, their end uses. The varieties of prominence are fibers and filaments, sheets and disposable soft-drink, soda drinks, juice, mineral water, soy sauce bottles, photographic films, etc. The world production of PET in 2002 was 26 million tons

crystallinity on final properties as well as biodegradability are investigated.

**2. Poly (ethylene terephthalate)** 

transesterification) with water as the byproduct (Fig.1-b).

Fig. 1. b. Polycondensation of BHET yields PET.

**3. PET waste, as an opportunity instead of a problem** 

which is expected to rise to 55 million ton in 2010. PET resin, or bottle grade, is one of the fastest growing plastics markets. Polyester fiber is the second largest segment, but the market is mature. The third use, film, is also a mature market, for example PET market in USA in 2008 could be shown in Fig.2.

Fig. 2. PET market in USA in 2008(chemsysytem.com,nexant ,PERP 07/08-5:1-8).

Large numbers of Post-consumer PET products especially bottles and containers do not create a direct hazard to the environment, but as a problem due to its substantial volume fraction in the solid waste streams, its high resistance to the atmosphere, its poor biodegradability and photo degradability. PET accounts for more than 8% by weight and 12% by volume of the world's solid waste (Shamsi R et al, 2009).

An estimated billion plastic bottles are disposed of each year, while recycling a single plastic bottle can conserve enough energy to light a 60 W light bulb for up to 6 h.

Recently, recycling of PET has received a great deal of attention and many attempts are currently directed toward recycling of post-consumer PET products because of both environmental protection and economic benefits. Also necessity for recycling of this product is felt more (Fig 3). In Singapore, 684,400 tones of plastic waste were generated in 2008 and the recycling rate was 9%. Although the nontoxic nature, durability and crystal clear transparency of PET during use are major advantages, its non biodegradability is the serious cause of concern to the environmentalists. Because it isn't appropriate to dispose of waste PET by land-filling, alternative methods of recycling of waste PET products include physical and chemical recycling have been developed.

To minimize the fast buildup of PET waste, different mechanical, thermal, and chemical methods to separate, recover and recycle PET from post-consumer waste stream have been used (Mohammadi M et al, 2010). Products made from recycled PET bottles include carpeting, concrete, insulation and automobile parts. Recycled PET bottles are also used in drainage filtration systems, asphalt concrete-mixes and road stabilizations. Recycling rate of such polymer products is however still low comparing to that of paper, glass and metals. Currently only 3.5% of generated polymeric products is recycled whereas these percentages for paper, glass and metals are, respectively, 34%, 22% and 30%.

Physical recycling of PET consists of the collection, separation, digestion, granulation of polymer waste and then recirculation into production. Blending of materials with PET waste

From PET Waste to Novel Polyurethanes 361

terephthalic acid (TPA) and ethylene glycol. During hydrolysis reaction, PET hydrolyzes to

Life time alternative in a PET chemical recycling plant is depicted in Fig 5. Kinetics of hydrolysis of PET Pellets in Nitric Acid (Mohammadi M et al, 2010), kinetics and Thermodynamics of Hydrolytic acidic and neutral depolymerization of poly (ethylene

Fig. 5. Life time alternative for PET chemical recycling, DMT (Dimethyl terephthalate), TPA

Glycolysis is breakdown of ester linkages by a glycol, resulting in oligomers or oligoester diols/polyols with hydroxyl terminal groups. Oligoesters coming from the glycolysis of PET

(Pure terephthalic acid) commonly uses PTA, EG (Ethylene Glycol).

terephthalate) at high pressure and temperature has been investigated.

a carboxylic acid and an alcohol as follows:

Fig. 4. Hydrolysis Reaction.

Fig. 6. Glycolysis Reaction.

**3.1.2 Glycolysis** 

has also been studied. The effect of waste PET addition on thermal transmission (or insulation) property of ordinary concrete has been studied and reported that corresponding percentages for PET bottle pieces vary between 10.27% and 18.16%, depending on the geometries of added pieces. Moreover, concrete-PET blends due to their ability in water absorption, a possible application could be in sports courts and pavements which need good water drainage. M.C. Almaza'n and co worker proposed a different method to obtain activated carbon using the actual waste plastic commercial vessels made of PET as raw material (Mohammadi M et al, 2010).

Fig. 3. PET waste as a threat, serious cause of concern to the environmentalists.

In a recyclability analysis determination of a global index which takes into account social, economic and environmental aspects is believed to be an interesting approach for industrial organizations. Thus, in this case following aspects may be analyzed:


#### **3.1 Chemical recycling of PET waste**

Chemical recycling of PET includes chemolysis of the polyester with an excess of reactants such as water (hydrolysis), alcohols (alcoholysis), glycols (glycolysis), amines (aminolysis) and ammonia (ammonolysis). (Shamsi R et al, 2009; Mohammadi et al, 2010 & Mir M. Sadeghi G et al, 2011).

#### **3.1.1 Hydrolysis**

PET is polyester, and the functional ester group can be hydrolyzed by water. Hydrolysis of PET can be carried out in an acid, alkaline or neutral environment to produce monomers

has also been studied. The effect of waste PET addition on thermal transmission (or insulation) property of ordinary concrete has been studied and reported that corresponding percentages for PET bottle pieces vary between 10.27% and 18.16%, depending on the geometries of added pieces. Moreover, concrete-PET blends due to their ability in water absorption, a possible application could be in sports courts and pavements which need good water drainage. M.C. Almaza'n and co worker proposed a different method to obtain activated carbon using the actual waste plastic commercial vessels made of PET as raw

 Fig. 3. PET waste as a threat, serious cause of concern to the environmentalists.

organizations. Thus, in this case following aspects may be analyzed:

In a recyclability analysis determination of a global index which takes into account social, economic and environmental aspects is believed to be an interesting approach for industrial


Chemical recycling of PET includes chemolysis of the polyester with an excess of reactants such as water (hydrolysis), alcohols (alcoholysis), glycols (glycolysis), amines (aminolysis) and ammonia (ammonolysis). (Shamsi R et al, 2009; Mohammadi et al, 2010 & Mir M.

PET is polyester, and the functional ester group can be hydrolyzed by water. Hydrolysis of PET can be carried out in an acid, alkaline or neutral environment to produce monomers

material (Mohammadi M et al, 2010).

polymer to a biodegradable one.

**3.1 Chemical recycling of PET waste** 

Sadeghi G et al, 2011).

**3.1.1 Hydrolysis** 

terephthalic acid (TPA) and ethylene glycol. During hydrolysis reaction, PET hydrolyzes to a carboxylic acid and an alcohol as follows:

Fig. 4. Hydrolysis Reaction.

Life time alternative in a PET chemical recycling plant is depicted in Fig 5. Kinetics of hydrolysis of PET Pellets in Nitric Acid (Mohammadi M et al, 2010), kinetics and Thermodynamics of Hydrolytic acidic and neutral depolymerization of poly (ethylene terephthalate) at high pressure and temperature has been investigated.

Fig. 5. Life time alternative for PET chemical recycling, DMT (Dimethyl terephthalate), TPA (Pure terephthalic acid) commonly uses PTA, EG (Ethylene Glycol).

Fig. 6. Glycolysis Reaction.

#### **3.1.2 Glycolysis**

Glycolysis is breakdown of ester linkages by a glycol, resulting in oligomers or oligoester diols/polyols with hydroxyl terminal groups. Oligoesters coming from the glycolysis of PET

From PET Waste to Novel Polyurethanes 363

products, such as BHETA, have the potential to undergo further reactions to yield secondary value-added products. In this direction, very recently the synthesis of unsaturated polyesters polyurethanes, epoxy resin hardeners and non-ionic polymeric

Zahn and Pfeifer carried out aminolysis of PET with solutions of hydrazine, benzyl amine, ethylene diamine, hexamethylene diamine, piperidine and aniline. They obtained different reaction products as the diamides of terephthalic acid, which do not possess any potential for further chemical reactions. According to Popoola the basicity of an amine relative to water as well as its steric hindrance due to size determines the rate of degradation of PET. During aminolysis of PET with methylamine, the methyl terephthalamide is obtained, which isn't enough reactive for its recycling into any useful product through further reactions. Shukla and Harad have been investigated the use of ethanolamine for the aminolytic degradation of PET waste in the presence of different simple chemicals such as glacial acetic acid, sodium acetate and potassium sulphate as catalysts. The product

Polyurethane is any polymer composed of a chain of organic units joined by carbamate (urethane) links. Polyurethane polymers are formed through step-growth polymerization, by reacting a reactant (with at least two isocyanate functional groups) with another reactant (with at least two hydroxyl or alcohol groups) in the presence of a catalyst. Generalized

R—NCO + R´—OH → R—NH—COO—R´ Thermoplastic polyurethanes (TPUs) are linear polymers formed by the polymerization

As shown in the above reactionurethane linkage is produced by reacting an isocyanate group,—N=C=O with a hydroxyl (alcohol) group,—OH. In fact, polyurethanes are produced by the polyaddition reaction of a polyisocyanate with a polyalcohol (polyol) in the presence of a catalyst and other additives. The reaction product is a polymer containing the urethane linkage, -RNHCOOR'-. A broad range of physical properties can be achieved by varying the chemistry and molecular weight of the various components, and through

obtained, BHETA has potential for further reactions to obtain useful products.

surfactants has been reported.

Fig. 8. Aminolysis reaction.

**4. Polyurethane** 

formation reaction of the urethane group is:

reaction of three basic components:

3. A long-chain diol (OH OH)

1. A diisocyanate ( NCO—R—NCO)

2. A short-chain diol, so-called chain extender (OH—R´—OH)

waste have been well known to be utilized as a starting material in the manufacture of unsaturated polyesters, vinyl ester resins, epoxy resins, alkyd resins and polyurethanes. Glycolysis is carried out using different glycols like; ethylene glycol, propylene glycol, 1, 4 butanediol and triethylene glycol, diethylene glycol (DEG), dipropylene glycol (DPG), glycerol (Gly) and etc. During glycolysis reaction, the organic group R″ of an ester with the organic group R′ of an alcohol exchanges. (Shamsi R et al, 2009; Mohamadi et al, 2010 & M. M. Sadeghi G et al, 2011)
