**2.4 Modifications and properties of recycling of virgin and waste PET**

Polyethylene terephthalate (PET) is a transparent semicrystalline, long-chain thermoplastic polyester which can be produced by a polymerization of terephthalic acid with ethylene glycol and remains the most used thermoplastics in many applications [55, 56]. It is characterized as easy to handle, durable, strong, thermally with low glass transition temperature, and chemically stable with low gas permeability [57]. It exhibits brittle behavior, good mechanical properties, and dimensional stability as well as good gas and chemical resistance which resulted to its wide applications [58]. Waste PET may be in bottles, foils, and cords from tire [57, 58]. Globally, the rate of generation of waste PET is about 20 million tonnes that amounted to about 15% which is alarming due to population growth, urbanization, standard of living, and cost of production, but the recycling rate of waste PET found to be 29.3% lower [56]. The issue with the reuse of waste PET may be associated with size, content, mixing process, type of mixer, temperature, time profile during mixing process, and contaminations or additives like stabilizers and pigments [58, 59]. In bitumen asphalt modification for the road construction, the mixing process may be wet or dry process. The wet process involves blending of thermoplastics and bitumen in a mixer and then mixing of thermoplastic modified bitumen to aggregates, while the latter involves incorporation of thermoplastics to very hot aggregates prior to mixing with bitumen [56]. Waste PET recycling employs dry process, and it can be modified to achieve better feasibility in terms of adhesion between the aggregates and binder, stability, and even mixing and minimizes the pore formation and moisture absorption. Appropriate recycling process conditions of waste PET make significant environmental and economy impacts through conservation of natural resources, environmental pollution, energy, and enhancement of engineering and physical properties of construction materials [58]. An increase in recycled PET content caused a decrease in melt flow index or rheological properties of the aggregate [29]. Recycled PET exhibits pseudo-plastic behavior, and it has been used to improve the rheological properties of asphalt as well as increased the viscosity and stiffness and enhanced the softening of stone mastic asphalt (SMA) [58].

Incorporation of recycled PET with appropriate content and size increased the compressive, tensile, and flexural strength/s and ductility of concrete, creates lightweight aggregate of development of building materials, or decreases the bulk density of the composites, thereby helping polymer concrete in saving energy and minimizing the problem of solid waste posed by PET as well as other thermoplastics provided the impurities were removed prior to reprocessing [58].

Synthetic thermoplastics such as HDPE and acrylonitrile butadiene styrene (ABS) blend nano silicon (IV) oxide (SiO2), and polylactic acid (PLA) can modify PET waste to improve its performance using the extrusion process based on a different mixing ratio. The use of virgin HDPE has been reported to improve rheological and mechanical properties when compared to waste PET using a less than 5% virgin HDPE [60]. The mechanical properties of composites of recycled PET improved with increase in incorporated nano silicate (SiO2) content blended with ABS [61]. Modification of PET waste by the addition of small amounts of virgin PLA using melt mixing technology also shows reduction in viscosity of the composites with higher thermal sensitivity and mechanical properties compared to recycled PET [50, 62]. It should be noted that the performance of recycling of waste PET was hindered due to the presence of impurities, decomposition, and degradation of polymer chains as reported by Imamura et al. [57]. The modifications by compatibilizer like ethylene glycidyl methacrylate (EGMA) modified PE copolymer significantly improved the miscibility of recycled PET with PP, PE,

**63**

*Thermoplastic Recycling: Properties, Modifications, and Applications*

PET size and content, and additive or modifier content.

and PS molecules, respectively, unlike linear low density polyethylene copolymer (LDPE) [57]. The use of natural materials to modify the properties of recycled PET such as fibers or fillers is not available in literature. The efficacy and performance of recycled PET applications required optimum conditions of modified process,

**2.5 Modifications and properties of recycling of virgin and waste polypropylene**

Due to favorable qualities of PP like density, versatility, photodegradation, and cheapness in cost of production, it is replacing many materials used for artifacts such as packaging products and automobile bumpers. The increasing rate of use of polypropylene coupled with inherent incompatibility of polyester and polyolefins seeks for improvement in the performance of PP in many applications [63]. The improvement in PP performance has been achieved through modification techniques by incorporation of grafted maleic anhydride (PP-g-MAH), clay-based nano-fillers, inorganic nanoscale particles, and poly(trimethylene terephthalate) (PTT) blends using organically modified montmorillonite (Cloisite nanoclays) as compatibilizers for the purpose of improving compatibility, mechanical, crystallization, and melting behavior of PP composites [64–66]. PTT is an aromatic polyester with combined properties of PET and poly(butylene terephthalate) (PBT). The factors that influence the properties of the PP composites are mix or blend ratio, crystallization temperature, compatibility process time, and size [63]. There is loss of mechanical properties for composites of LDPE and HDPE modified with PP which is due to incompatibility of recycled PP/LDPE and PP/HDPE composites [39]. The modification of recycled PP with HDPE reveals a partial compatibility which caused an improvement in tensile strength and elongation with the use of EPDM compatibilizer [67]. The modification of recycled LDPE/PP with 1% montmorillonite nanoclay exhibits appreciable improvement in strength, physical

*DOI: http://dx.doi.org/10.5772/intechopen.81614*

properties, and stability of bitumen [68].

**3.1 Fourier-transform infrared spectroscopy**

**and its modifications**

subSection 3.1.

**3. Microstructural behavior of recycled thermoplastic matrix** 

The microstructural behavior in this content is limited to Fourier-

transform infrared spectroscopy and scanning electron microscopy as discussed in

FTIR analysis of recycled thermoplastics exhibits no extra peaks for the blends, neither any shifts nor changes in the absorption bands of the carbonyl, hydroxyl, and carboxylic groups of HDPE, LDPE, PET, PVC, and PP resins which indicates the absence of any specific interaction, entanglement, or chemical reaction between the polymers and modifiers as reported by Mamoor et al. (**Figure 3**) [29]. In the case of modification of recycled thermoplastics using untreated natural fiber, there exists a shift or change in the absorption peaks of the carbonyl, hydroxyl, and carboxylic groups of the fiber-reinforced recycled thermoplastics, thereby influencing the physical and mechanical properties of the matrix and interfacial between the fiber and HDPE as reported by researchers [21, 69]. This resulted in improved quality of the thermoplastic products. The shift, change, appearance, and disappearance of absorption peaks correspond to reaction of the functional groups. This

### *Thermoplastic Recycling: Properties, Modifications, and Applications DOI: http://dx.doi.org/10.5772/intechopen.81614*

*Thermosoftening Plastics*

**2.4 Modifications and properties of recycling of virgin and waste PET**

provided the impurities were removed prior to reprocessing [58].

Synthetic thermoplastics such as HDPE and acrylonitrile butadiene styrene (ABS) blend nano silicon (IV) oxide (SiO2), and polylactic acid (PLA) can modify PET waste to improve its performance using the extrusion process based on a different mixing ratio. The use of virgin HDPE has been reported to improve rheological and mechanical properties when compared to waste PET using a less than 5% virgin HDPE [60]. The mechanical properties of composites of recycled PET improved with increase in incorporated nano silicate (SiO2) content blended with ABS [61]. Modification of PET waste by the addition of small amounts of virgin PLA using melt mixing technology also shows reduction in viscosity of the composites with higher thermal sensitivity and mechanical properties compared to recycled PET [50, 62]. It should be noted that the performance of recycling of waste PET was hindered due to the presence of impurities, decomposition, and degradation of polymer chains as reported by Imamura et al. [57]. The modifications by compatibilizer like ethylene glycidyl methacrylate (EGMA) modified PE copolymer significantly improved the miscibility of recycled PET with PP, PE,

Polyethylene terephthalate (PET) is a transparent semicrystalline, long-chain thermoplastic polyester which can be produced by a polymerization of terephthalic acid with ethylene glycol and remains the most used thermoplastics in many applications [55, 56]. It is characterized as easy to handle, durable, strong, thermally with low glass transition temperature, and chemically stable with low gas permeability [57]. It exhibits brittle behavior, good mechanical properties, and dimensional stability as well as good gas and chemical resistance which resulted to its wide applications [58]. Waste PET may be in bottles, foils, and cords from tire [57, 58]. Globally, the rate of generation of waste PET is about 20 million tonnes that amounted to about 15% which is alarming due to population growth, urbanization, standard of living, and cost of production, but the recycling rate of waste PET found to be 29.3% lower [56]. The issue with the reuse of waste PET may be associated with size, content, mixing process, type of mixer, temperature, time profile during mixing process, and contaminations or additives like stabilizers and pigments [58, 59]. In bitumen asphalt modification for the road construction, the mixing process may be wet or dry process. The wet process involves blending of thermoplastics and bitumen in a mixer and then mixing of thermoplastic modified bitumen to aggregates, while the latter involves incorporation of thermoplastics to very hot aggregates prior to mixing with bitumen [56]. Waste PET recycling employs dry process, and it can be modified to achieve better feasibility in terms of adhesion between the aggregates and binder, stability, and even mixing and minimizes the pore formation and moisture absorption. Appropriate recycling process conditions of waste PET make significant environmental and economy impacts through conservation of natural resources, environmental pollution, energy, and enhancement of engineering and physical properties of construction materials [58]. An increase in recycled PET content caused a decrease in melt flow index or rheological properties of the aggregate [29]. Recycled PET exhibits pseudo-plastic behavior, and it has been used to improve the rheological properties of asphalt as well as increased the viscosity and stiffness and enhanced the softening of stone mastic asphalt (SMA) [58]. Incorporation of recycled PET with appropriate content and size increased the compressive, tensile, and flexural strength/s and ductility of concrete, creates lightweight aggregate of development of building materials, or decreases the bulk density of the composites, thereby helping polymer concrete in saving energy and minimizing the problem of solid waste posed by PET as well as other thermoplastics

**62**

and PS molecules, respectively, unlike linear low density polyethylene copolymer (LDPE) [57]. The use of natural materials to modify the properties of recycled PET such as fibers or fillers is not available in literature. The efficacy and performance of recycled PET applications required optimum conditions of modified process, PET size and content, and additive or modifier content.
