**3.1.4 Aminolysis**

Aminolysis is another method of chemical degradation of PET, which has been relatively little investigated, compared to the other techniques.

Fig. 7. Using of BHET (glycolysis product of PET waste) to obtain other materials.

Depolymerization of PET waste has been carried out using various amines, such as ethanolamine, benzylamine, hexamethylenediamine, aniline, methylamine hydrazine monohydrate and some polyamines. Catalysts such as lead acetate, glacial acetic acid, sodium acetate and potassium sulfate are usually used to facilitate the reaction. Aminolysis

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.

Methanolysis is the degradation of PET using methanol at high temperatures and high pressures with the main products being dimethyl terephthalate (DMT) and ethylene glycol. Methanolysis is the recycling process which has been practiced and tested on a large scale for many years in the past. In this case, polyester waste is transformed with methanol into DMT (Dimethyl terephthalate), under pressure and in presence of catalysts. Finally the crude DMT is purified by vacuum distillation. Degradation of PET using ethylene glycol at high temperatures and high pressures with the main products being BHET is used to produce some different materials such as polyester, polyurethane resins and esteric

Aminolysis is another method of chemical degradation of PET, which has been relatively

Fig. 7. Using of BHET (glycolysis product of PET waste) to obtain other materials.

Depolymerization of PET waste has been carried out using various amines, such as ethanolamine, benzylamine, hexamethylenediamine, aniline, methylamine hydrazine monohydrate and some polyamines. Catalysts such as lead acetate, glacial acetic acid, sodium acetate and potassium sulfate are usually used to facilitate the reaction. Aminolysis

M. Sadeghi G et al, 2011)

plasticizer, as shown in Fig. 7.

little investigated, compared to the other techniques.

**3.1.4 Aminolysis** 

**3.1.3 Methanolysis** 

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 surfactants has been reported.

$$\begin{array}{c} \text{O} \\ \text{-C-}\bigotimes \text{-C-}\bigotimes \text{-CH}\_{2}\text{-CH}\_{2}\text{-O-}\bigotimes \\ \qquad \Big\downarrow \\ \text{H}\_{3}\text{C-N-}\text{-C-}\bigotimes \text{-CH}\_{2}\text{-CH}\_{3}\text{-CH}\_{2}\text{-CH}\_{2}\text{-CH}\_{2}\text{-CH}\_{2}\text{-OH}-\text{H}\text{-}\text{H}\text{-}\text{CH}\_{2}\text{-CH}\_{2}\text{-OH} \end{array}$$

Fig. 8. Aminolysis reaction.

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

#### **4. Polyurethane**

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 formation reaction of the urethane group is:

$$\text{R}-\text{NCO} + \text{R}'-\text{OH} \quad \rightarrow \quad \text{R}-\text{NH}-\text{COO}-\text{R}'$$

Thermoplastic polyurethanes (TPUs) are linear polymers formed by the polymerization reaction of three basic components:


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

From PET Waste to Novel Polyurethanes 365

**4.2.1. Hard Segments** which are segments formed by the reaction of the diisocyanate and the short-chain diol. They have a high density of urethane groups of high polarity, and for

**4.2.2. Soft Segments** which are segments formed by the reaction of the diisocyanate and the long-chain diol. They have a low polarity as they have a very low density of urethane groups, and therefore, they are flexible at room temperature (very low hardness). A general

The polarity of hard segments produces a strong attraction between them, which causes a high degree of aggregation and order in this phase, forming crystalline or pseudo-crystalline areas located in a soft and flexible matrix. This so-called phase separation between both blocks will be more or less important, depending on the polarity and molecular weight of the flexible chain, the production conditions, etc. The crystalline or pseudo-crystalline areas act as a physical crosslink, which accounts for the high elasticity level of TPUs, where as the flexible chains will impart the elongation characteristics to the polymer. The schematic representation of the segmented micro structure and two-phase morphology of polyurethane are shown in Figs. 10 and 11. These "pseudo crosslinks" , based on hydrogen bonding between carbonyl groups and –NH groups of various chains , however, disappear under the effect of heat, and thus the classical extrusion, injection molding and calendaring

Fig. 10. Schematic represent of microstructure of segmented polyurethane chains.

Consequently –and not less importantly- TPU scraps can be reprocessed. When TPUs are cold, the "pseudocrosslinks" reappear again, providing the elastic properties to the obtained

this reason, they are rigid at room temperature (high hardness).

structure of thermoplastic polyurethane's chain would be as Fig. 9:

Fig. 9. General structure of polyurethane's chain.

processing methods are applicable to these materials.

manipulation of the ratios in which they are reacted in polyurethanes. Therefore polyurethanes have received recent attention as regards the development of wide family of polymeric materials (paints, adhesives, elastomers, flexible, and rigid foams, etc.) and thus play an important and increasing role in our daily life. The greatest advantage offered by polyurethane is their versatility, both in finished product properties and ease of production and application. By the proper choice of isocyanate and polyol, products can be made with properties ranging from low viscosity resins used in printing to high modulus solids used in industrial parts. Polyurethanes are applied to the manufacture of flexible, high-resilience foam seating; rigid foam insulation panels; microcellular foam seals and gaskets; durable elastomeric wheels and tires; automotive suspension bushings; electrical potting compounds; high performance adhesives; surface coatings and surface sealants; synthetic fibers (e.g. Spandex); carpet underlay; and hard-plastic parts (i.e. for electronic instruments) and any other industrial parts.
