**4.1 Components**

**Polyols** are higher molecular weight materials manufactured from an initiator and monomeric building blocks. They are most easily classified as polyether polyols, which are made by the reaction of epoxides (oxiranes) with active hydrogen containing starter compounds, or polyester polyols, which are made by the polycondensation of multifunctional carboxylic acids and hydroxyl compounds.

**Isocyanates** two or more functional groups are required for the formation of polyurethane polymers. Volume wise, aromatic isocyanates account for the vast majority of global diisocyanate production. Aliphatic and cycloaliphatic isocyanates are also important building blocks for polyurethane materials, but in much smaller volumes. The two most important commercial, aromatic isocyanates are toluene diisocyanate (TDI) and diphenylmethane diisocyanate (MDI). TDI consists of a mixture of the 2,4- and 2,6 diisocyanatotoluene isomers. The most important product is TDI-80 (TD-80), consisting of 80% of the 2,4-isomer and 20% of the 2,6-isomer. This blend is used extensively in the manufacture of polyurethane flexible slabstock and molded foam. TDI, and especially crude TDI and TDI/MDI blends can be used in rigid foam applications, but have been supplanted by polymeric MDI. TDI-polyether and TDI-polyester prepolymers are used in high performance coating and elastomeric applications.

**Chain extenders (f =2) and cross linkers (f =3 or** greater) are low molecular weight hydroxyl and amine terminated compounds that play an important role in the polymer morphology of polyurethanes. The choice of chain extender also determines flexural, heat, and chemical resistance properties. The most important chain extenders are ethylene glycol, 1,4-butanediol(1,4-BDO or BDO),1,6-hexanediol,cyclohexane,dimethanol and hydroquinone bis (2-hydroxyethyl) ether (HQEE).

#### **4.2 Microstructure of polyurethanes**

Segmented polyurethanes that consist of alternating soft and hard segments offer unique possibilities of tailor-made polymers by varying block length and composition. The structure of the lineal polymeric chain of thermoplastic polyurethane is in blocks, alternating two different types of segments linked together by covalent links, forming a block copolymer. These segments are:

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)

**Polyols** are higher molecular weight materials manufactured from an initiator and monomeric building blocks. They are most easily classified as polyether polyols, which are made by the reaction of epoxides (oxiranes) with active hydrogen containing starter compounds, or polyester polyols, which are made by the polycondensation of

**Isocyanates** two or more functional groups are required for the formation of polyurethane polymers. Volume wise, aromatic isocyanates account for the vast majority of global diisocyanate production. Aliphatic and cycloaliphatic isocyanates are also important building blocks for polyurethane materials, but in much smaller volumes. The two most important commercial, aromatic isocyanates are toluene diisocyanate (TDI) and diphenylmethane diisocyanate (MDI). TDI consists of a mixture of the 2,4- and 2,6 diisocyanatotoluene isomers. The most important product is TDI-80 (TD-80), consisting of 80% of the 2,4-isomer and 20% of the 2,6-isomer. This blend is used extensively in the manufacture of polyurethane flexible slabstock and molded foam. TDI, and especially crude TDI and TDI/MDI blends can be used in rigid foam applications, but have been supplanted by polymeric MDI. TDI-polyether and TDI-polyester prepolymers are used in high

**Chain extenders (f =2) and cross linkers (f =3 or** greater) are low molecular weight hydroxyl and amine terminated compounds that play an important role in the polymer morphology of polyurethanes. The choice of chain extender also determines flexural, heat, and chemical resistance properties. The most important chain extenders are ethylene glycol, 1,4-butanediol(1,4-BDO or BDO),1,6-hexanediol,cyclohexane,dimethanol and hydroquinone

Segmented polyurethanes that consist of alternating soft and hard segments offer unique possibilities of tailor-made polymers by varying block length and composition. The structure of the lineal polymeric chain of thermoplastic polyurethane is in blocks, alternating two different types of segments linked together by covalent links, forming a

and any other industrial parts.

multifunctional carboxylic acids and hydroxyl compounds.

performance coating and elastomeric applications.

bis (2-hydroxyethyl) ether (HQEE).

**4.2 Microstructure of polyurethanes** 

block copolymer. These segments are:

**4.1 Components** 

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

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

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

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 processing methods are applicable to these materials.

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

From PET Waste to Novel Polyurethanes 367

Schematic representation of the superstructure (domain and chain formation) and dimensions in polyurethanes is shown in Fig.12. This phase separation occurs because the mainly non-polar, low melting soft segments are incompatible with the polar, high melting hard segments. The soft segments, which are formed from high molecular weight polyols, are mobile and are normally present in coiled formation, while the hard segments, which are formed from the isocyanate and chain extenders, are stiff and immobile. Because the hard segments are covalently coupled to the soft segments, they inhibit plastic flow of the

Fig. 12. Schematic representation of superstructure (domain and chain formation) in

Fig. 13. Schematic representation of soft and hard segments thermal transitions.

segment content affects on mechanical as well as their thermal properties definitely.

**4.4 Wide variety of soft & hard segments in synthesis of polyurethanes** 

Upon mechanical deformation, a portion of the soft segments are stressed by uncoiling, and the hard segments become aligned in the stress direction. This reorientation of the hard segments and consequent powerful hydrogen bonding contributes to high tensile strength, elongation, and tear resistance values. Phase separation in polyurethanes can be studied by dynamic thermal analysis. Thermal transitions of hard and soft segments of a typical polyurethane consisted of a soft rubbery phase and hard phase are presented in Fig. 13. According to nature and physical chemistry properties of polyurethanes, increasing of hard

A broad range of physical properties can be achieved by varying the chemical structure and molecular weight of the various components and also through manipulation of the ratios in

polymer chains, thus creating elastomeric resiliency.

polyurethanes.

article. When TPUs are dissolved in a proper solvent, the "pseudo crosslinks" are also broken up by the solvent, and therefore, disappear. Due to this it is possible to apply a TPU in solution by classical methods of coating applications; when the solvent evaporates the "pseudo crosslinks" are formed again.

The soft domains provide the thermoplastic polyurethane with a very low Tg, in comparison with other polymers of the same hardness, maintaining the elasticity at very low temperatures. The presence of polar and non polar counter balanced microdomains is the cause of the good chemical resistance of TPUs, particularly oil and grease resistance. Thermoplastic polyurethanes are very versatile items, since a variety of soft and hard segments can be combined, with their respective ranges of molecular weights, and considering also the variety of molecular weights of the final polymer.

So that it is possible to obtain from very soft (60 Shore A) to very hard polyurethanes (80 Shore D), with different degrees of crystallinity, to be used in many applications and market segments which require high performance. This peculiar structure which differentiates thermoplastic polyurethanes from other polymers provides polyurethanes with the following main properties:


#### **4.3 Morphology**

Chain extenders play an important role in the polymer morphology of polyurethane fibers, elastomers, adhesives, and certain integral skin and microcellular foams. The elastomeric properties of these materials are derived from the phase separation of the hard and soft copolymer segments of the polymer, such that the urethane hard segment domains serve as cross-links between the amorphous polyether (or polyester) soft segment domains.

Fig. 11. Schematic representation of two-phase morphology in polyurethanes.

article. When TPUs are dissolved in a proper solvent, the "pseudo crosslinks" are also broken up by the solvent, and therefore, disappear. Due to this it is possible to apply a TPU in solution by classical methods of coating applications; when the solvent evaporates the

The soft domains provide the thermoplastic polyurethane with a very low Tg, in comparison with other polymers of the same hardness, maintaining the elasticity at very low temperatures. The presence of polar and non polar counter balanced microdomains is the cause of the good chemical resistance of TPUs, particularly oil and grease resistance. Thermoplastic polyurethanes are very versatile items, since a variety of soft and hard segments can be combined, with their respective ranges of molecular weights, and

So that it is possible to obtain from very soft (60 Shore A) to very hard polyurethanes (80 Shore D), with different degrees of crystallinity, to be used in many applications and market segments which require high performance. This peculiar structure which differentiates thermoplastic polyurethanes from other polymers provides polyurethanes with the

Chain extenders play an important role in the polymer morphology of polyurethane fibers, elastomers, adhesives, and certain integral skin and microcellular foams. The elastomeric properties of these materials are derived from the phase separation of the hard and soft copolymer segments of the polymer, such that the urethane hard segment domains serve as

cross-links between the amorphous polyether (or polyester) soft segment domains.

Fig. 11. Schematic representation of two-phase morphology in polyurethanes.

considering also the variety of molecular weights of the final polymer.

• Excellent mechanical properties, combined with a rubber-like elasticity

"pseudo crosslinks" are formed again.

following main properties: • Very high elasticity

• High transparency

**4.3 Morphology** 

• Excellent abrasion resistance • Very good tear strength • Good oil and grease resistance

• Outstanding low-temperature performance

Schematic representation of the superstructure (domain and chain formation) and dimensions in polyurethanes is shown in Fig.12. This phase separation occurs because the mainly non-polar, low melting soft segments are incompatible with the polar, high melting hard segments. The soft segments, which are formed from high molecular weight polyols, are mobile and are normally present in coiled formation, while the hard segments, which are formed from the isocyanate and chain extenders, are stiff and immobile. Because the hard segments are covalently coupled to the soft segments, they inhibit plastic flow of the polymer chains, thus creating elastomeric resiliency.

Fig. 12. Schematic representation of superstructure (domain and chain formation) in polyurethanes.

Fig. 13. Schematic representation of soft and hard segments thermal transitions.

Upon mechanical deformation, a portion of the soft segments are stressed by uncoiling, and the hard segments become aligned in the stress direction. This reorientation of the hard segments and consequent powerful hydrogen bonding contributes to high tensile strength, elongation, and tear resistance values. Phase separation in polyurethanes can be studied by dynamic thermal analysis. Thermal transitions of hard and soft segments of a typical polyurethane consisted of a soft rubbery phase and hard phase are presented in Fig. 13. According to nature and physical chemistry properties of polyurethanes, increasing of hard segment content affects on mechanical as well as their thermal properties definitely.

#### **4.4 Wide variety of soft & hard segments in synthesis of polyurethanes**

A broad range of physical properties can be achieved by varying the chemical structure and molecular weight of the various components and also through manipulation of the ratios in

From PET Waste to Novel Polyurethanes 369

chain extender. The purified BHETA was characterized by FTIR, 1HNMR, and melting

Fig. 14. Depolymerization mechanism of (2-hydroxy ethylene) Terephthalamide.

depolymerized and expected product (BHETA) was synthesized successfully.

Fig. 15. 1HNMR spectrum of BHETA.

The FTIR spectrograph of the purified As can be seen, the shift and splitting pattern of 1H NMR at 8.52 ppm, 7.91ppm , 4.73 ppm, 3.52 ppm and 3.34 ppm, corresponding to H of the amine group, aromatic ring, hydroxyl Group, CH2 bonded to hydroxyl group, and CH2 bonded to amine group respectively. These obtained results confirmed that the PET fibers

point. Synthesized BHETA has been melted at 227°C.

which they are reacted in polyurethanes. Therefore, polyurethanes have received recent attention with regard to the development of degradable polymers because of their great potential in tailoring polymer structures to achieve mechanical properties and biodegradability to suit variety of applications such as biodegradable polymers, soft tissue adhesives, clinical demand and meniscus scaffold. Multiblock copolymers based on caprolactone and lactic acid, polyglycoles, polyesters and multifunctional aliphatic carboxylic acids as soft segments have been investigated used in various applications such as medical or industrial fields. Commercial polycaprolactones with different molecular weights as a soft segment, Polycaprolactone-based polyurethanes using diols such as Ethyleneglycole BHET, 1,4-butanediol or other diols as chain extender for ring opening polymerization of caprolactone have been studied. Using of nature-based polyols to prepare polyurethane foams is common but there are few reports on elastomeric polyurethane. Presence of aromatic ring in PET structure caused to improve mechanical and thermal properties of polyurethane structure; while presence of esteric bonds leads to biodegradation. (Yeganeh et al, 2007; Heijka R et al, 2005)
