**2. Recycling of modified virgin and waste thermoplastics**

The choice of recycling of waste thermoplastics depends on processing equipment such as injection, single-screw extruder and film blowing machine, and processing conditions (temperature, time, content of materials, and rheological behavior) and product uses [27–32]. The application of additives or modifiers like compatibilizer (nonreactive and reactive), fillers or fibers (inorganic and organic) have been attributed to ease processing and improvement in compatibility [28, 31]. More so, the recycling of waste thermoplastics is cheaper than virgin types, but its inferior properties [20, 21], contaminations, and poor suitability [33] remain an

**57**

ductile HDPE polymers [35].

*Thermoplastic Recycling: Properties, Modifications, and Applications*

excision of chain and radicals of thermoplastics [36].

**2.1 Modifications and properties of recycling of virgin and waste HDPE**

The incorporation of the carbon nanotube, zeolite, LDPE, PP, natural fillers, and fibers with treatment into the waste polymer for reuse has resulted to an improvement of the composite strength and enhancement of compatibility of blended components of composites as presented in **Table 3**. The improvement has been reported to be a function of compatibilizer types, size and particle shape, branching, and dimensions of polymeric chains as reported by [37]. In the case of natural fibers or fillers, it seems fibers or fillers containing compatibilizer which may or may not have been identified. Moreover, the melting flow rate of recycling of postconsumer or waste HDPE remains inconsistent with stabilization, and the consistency can be achieved with a mixture of phosphite and phenolic. This might be uneconomical. The enhancement in mechanical properties and performance of the HDPE matrix and composite product by additives (sodium hydroxide (NaOH), sodium lauryl sulfate (SLS), and acetic anhydride) have also been attributed to increased interfacial adhesion coupled with its improved water absorption [21], biodegradability, biocompatibility, antimicrobial activity, and non-toxicity with the use of chitosan compounds [38]. The density of recycled virgin and waste HDPE is within the range of 0.02–0.96 g/cm3

Increase in density can be ascribed to chemocrystallization, annealing effects and changes in lamellar orientation, fiber loading, moisture absorption, and aging of HDPE products [35]. Annealing effect involves changes in spherulite size of HDPE material after heat effect, and aged surface shows loss of gloss observed as a result of environmental effect through oxidative stress and disappearance of crystalline molecule of the HDPE materials produced by a surface contraction. The surface contractions initiate micro-cracks and lead to embrittlement of

[36, 39].

issue of concern for effective applications. Blending technology remains a proffer solution due to low cost to produce, lower technical risk, and eco-friendly materials when compared to developing new polymers [28]. Sorting or separation before recycling through manual [34] application of principle of density and solubilization with the use of solvents (hexane, benzene, xylene, and toluene) provides solution to contamination [2] but not cost effect and risk. Techniques for modifications of thermoplastics may be due to the use of different waste or virgin thermoplastics and natural materials, thereby producing composites with enhanced properties and durability [35]. This can be influenced by processing, crystallization, and phase morphology as reported by Lin et al. [32]. The use of different waste or virgin thermoplastics seems to be uneconomical due to cost of blended and non-compatibility of the thermoplastics which may require a new compatibilizer. The use of natural materials for modification of virgin and waste thermoplastics remains a potential technique for thermoplastic recyclates. Therefore, the major reasons for modification of plastic resins in the industries include to meet specific processing and performance specification of a plastic product that is not satisfied by a single component, to upgrade the properties of postconsumer plastic wastes, for scientific research, for interest and development, and for financial optimization [31, 32]. However, degradation of thermoplastic materials by chemical processes is a function of reaction between the components and the environment. The reduction in photodegradation of thermoplastics by ultraviolet absorber as an antioxidant shows a retardation effect of oxidation [36]. Therefore, the aging process of thermoplastics can be influenced by the synergistic action of factors like electromagnetic radiation and thermal energy on the oxidation, favoring the initiation of degradation by

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

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

*Thermosoftening Plastics*

with ISO 15270, namely:

pretreatment or decontamination.

to mechanical recycling.

Waste polymer recycling can be carried out by four approaches in accordance

1.Primary recycling refers to the recycling of the scrap material of controlled history. This process remaining to be the most popular as it ensures simplicity, low cost, and applicability to clean uncontaminated single-type waste. It involves melting with use of solvents and remolding of clean materials [19].

2.Mechanical recycling: waste plastic is recycled or reprocessed by mechanical process using melt extrusion, injection, blowing, vacuum, and inflation molding method after sorting [2, 20, 21]. This method utilizes a 100% utilization and conversion of waste plastic to produce the same or other valuable products but with reduced qualities which can be enhanced by the application of additives. It may or may not be necessarily separated depending on desired products and quality. It is applicable to reprocessing plastics that require

3.Chemical or feedstock recycling: waste plastics serve as raw materials and convert into monomer or other products such as fuel oils and cooking gas through decomposition and depolymerization of feedstock with the use of thermal energy or catalyst [22, 23]. This method seems to be economical but reduced the yield of new products [24] and less than the yield of the mechanical recycling of thermoplastics due to no loss of materials and accumulation caused by pipeline blockage as a result of shutdown of the machine, thereby lowering melting points during solidification stages. Pipeline blockages or clogs may be difficult to remove. This method involves decomposition of waste polymers to lower-molecular-weight species for reuse with applications of solvents like benzene, chlorobenzene, trichloroethylene, toluene, and xylene called dissolution/reprecipitation (DR) or solubilization before pyrolysis (applied high temperature and pressure in the absence of oxygen) [25]. This provides an insight to the solution of clogged pipeline issues but at increased processing cost and time with high-energy consumption compared

4.Energy recovery: This is an effective means to reduce the quantity of organic materials by incineration, with difficult environment pollution control from the waste plastics [24, 26]. It involves cement kiln and waste power generation.

This chapter focuses on modifications of thermoplastic materials (HDPE, LDPE,

The choice of recycling of waste thermoplastics depends on processing equipment such as injection, single-screw extruder and film blowing machine, and processing conditions (temperature, time, content of materials, and rheological behavior) and product uses [27–32]. The application of additives or modifiers like compatibilizer (nonreactive and reactive), fillers or fibers (inorganic and organic) have been attributed to ease processing and improvement in compatibility [28, 31]. More so, the recycling of waste thermoplastics is cheaper than virgin types, but its inferior properties [20, 21], contaminations, and poor suitability [33] remain an

PVC, PET, and PP) and mechanical recycling for enhanced properties, perfor-

mance, and quality of the products for sustainable applications.

**2. Recycling of modified virgin and waste thermoplastics**

**56**

issue of concern for effective applications. Blending technology remains a proffer solution due to low cost to produce, lower technical risk, and eco-friendly materials when compared to developing new polymers [28]. Sorting or separation before recycling through manual [34] application of principle of density and solubilization with the use of solvents (hexane, benzene, xylene, and toluene) provides solution to contamination [2] but not cost effect and risk. Techniques for modifications of thermoplastics may be due to the use of different waste or virgin thermoplastics and natural materials, thereby producing composites with enhanced properties and durability [35]. This can be influenced by processing, crystallization, and phase morphology as reported by Lin et al. [32]. The use of different waste or virgin thermoplastics seems to be uneconomical due to cost of blended and non-compatibility of the thermoplastics which may require a new compatibilizer. The use of natural materials for modification of virgin and waste thermoplastics remains a potential technique for thermoplastic recyclates. Therefore, the major reasons for modification of plastic resins in the industries include to meet specific processing and performance specification of a plastic product that is not satisfied by a single component, to upgrade the properties of postconsumer plastic wastes, for scientific research, for interest and development, and for financial optimization [31, 32]. However, degradation of thermoplastic materials by chemical processes is a function of reaction between the components and the environment. The reduction in photodegradation of thermoplastics by ultraviolet absorber as an antioxidant shows a retardation effect of oxidation [36]. Therefore, the aging process of thermoplastics can be influenced by the synergistic action of factors like electromagnetic radiation and thermal energy on the oxidation, favoring the initiation of degradation by excision of chain and radicals of thermoplastics [36].

## **2.1 Modifications and properties of recycling of virgin and waste HDPE**

The incorporation of the carbon nanotube, zeolite, LDPE, PP, natural fillers, and fibers with treatment into the waste polymer for reuse has resulted to an improvement of the composite strength and enhancement of compatibility of blended components of composites as presented in **Table 3**. The improvement has been reported to be a function of compatibilizer types, size and particle shape, branching, and dimensions of polymeric chains as reported by [37]. In the case of natural fibers or fillers, it seems fibers or fillers containing compatibilizer which may or may not have been identified. Moreover, the melting flow rate of recycling of postconsumer or waste HDPE remains inconsistent with stabilization, and the consistency can be achieved with a mixture of phosphite and phenolic. This might be uneconomical. The enhancement in mechanical properties and performance of the HDPE matrix and composite product by additives (sodium hydroxide (NaOH), sodium lauryl sulfate (SLS), and acetic anhydride) have also been attributed to increased interfacial adhesion coupled with its improved water absorption [21], biodegradability, biocompatibility, antimicrobial activity, and non-toxicity with the use of chitosan compounds [38]. The density of recycled virgin and waste HDPE is within the range of 0.02–0.96 g/cm3 [36, 39]. Increase in density can be ascribed to chemocrystallization, annealing effects and changes in lamellar orientation, fiber loading, moisture absorption, and aging of HDPE products [35]. Annealing effect involves changes in spherulite size of HDPE material after heat effect, and aged surface shows loss of gloss observed as a result of environmental effect through oxidative stress and disappearance of crystalline molecule of the HDPE materials produced by a surface contraction. The surface contractions initiate micro-cracks and lead to embrittlement of ductile HDPE polymers [35].


*Thermosoftening Plastics*

**Table 3.**

**59**

**Table 4.**

*Thermoplastic Recycling: Properties, Modifications, and Applications*

**2.2 Modifications and properties of recycling of virgin and waste LDPE**

with influence of aging of the product have not motivated utilization in many packaging applications such as bags, film, and pallet covers, but modifications may improve the mechanical properties. Also, the qualities of LDPE composites have been linked with poor interfacial adhesion between both phases of individual constituents which explain weak mechanical properties. This interfacial adhesion has a direct relation to compatibility. The processing conditions of machine also influenced the compatibility of the polymers. Some modifications of LDPE are presented in **Table 4**. The use of virgin and waste or recycled PP to modify LDPE using twin and single-screw extruder has been reported by Sylvie and Jean-jacques [12]. In the report, PP increases some mechanical properties such as tensile strength and modulus with reduced impact strength of the LDPE for single extruding machine, although the twin extruding machine gave better mechanical properties due to improvement in homogeneity of the polymer. The use of compatibilizer such as EPDM, graft copolymer (PE-g-poly (2-methyl-1,3-butadiene), and

> **strength (MPa)**

Virgin LDPE Virgin PP 25.1 5.5–6.5 [36]

Waste LDPE Waste 10% PP 8.7–12.1 241–336.1 23–37.2 [41]

Waste LDPE — 30.33 240.7 2.3 583 [47] Waste LDPE Husk filler 31.58 565.7 13.15 600 [48]

Waste LDPE 10% PP 10.0 248 12.3 [12]

19.5–22.9 195.73–

**Tensile modulus (MPa)**

232.14

236.1

Okpa filler 35.14 861.2 17.53 583 [47]

9.6 226 8.5

10.3 256 12.6

11.8 280 12.5

10.1 245 16.5

**Hardness Impact** 

16.34 520.16 — — [45]

9.4 205 15.2 [12]

**strength (J/m2 )**

18–26 [37]

46.4–53 [36]

**References**

The high quantity of waste LDPE and its average mechanical properties coupled

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

**Thermoplastics Modification Tensile** 

maleic anhydride

clinoptilolite (K2,Na2,Ca)Al6Si3O72. 23H2O of 1–2% with particle size <40 μm

Waste LDPE Waste 10% PP + EPDM 7.6–8.5 211.1–

screw extruder

screw extruder

screw extruder

copolymer using twin screw extruder

> using twin screw extruder

*Mechanical properties of unmodified and modified virgin and waste LDPE.*

Virgin LDPE Starch grafted with

Waste LDPE Natural zeolite,

Virgin LDPE 10% PP using single-

Virgin LDPE 10% PP using twin

Waste LDPE 10% PP using twin

Waste LDPE 10% PP + 5% graft

Waste LDPE 10% PP + 5% EPDM

*Mechanical properties of modified virgin and waste HDPE materials.*

*Thermosoftening Plastics*

**58**

**Materials**

Virgin

—

HDPE

Virgin

Using LDPE

22.5

860

—

—

—

135

5

[40]

[28]

HDPE

Virgin

3% Carbon nanotube and 2 cycles

36

1700

HDPE

Waste

Natural zeolite, clinoptilolite (K2,Na2,Ca)

21.8

218

—

—

—

25

[37]

HDPE

Waste

HDPE

Al6Si

O3 72. 23H

O of 1–2% with particle size 2

<40 μm

—

*Combretum dolichopetalum* fiber

Acetic anhydride-treated *Combretum* 

*dolichopetalum* fiber

NaOH-treated *Combretum dolichopetalum*

34.9041

984.99

32.067

2277.15

39

469.5912

fiber

—

*Cissus populnea* fiber

*Cissus populnea* fiber treated with NaOH

*Cissus populnea* fiber treated with SLS

**Table 3.**

*Mechanical properties of modified virgin and waste HDPE materials.*

31.8013

823.245

39.568

1455.68

38

394.683

29.6903

793.05

39.3962

1568.44

35

398.62

27.628 30.4827

839.022

36.1904

1425.89

30

155.795

792.59

34.519

1390.7

24

962.8

[21]

Waste

HDPE

24.619 32.427 38.5153

1220

8.5111

19944.24

33

787.3806

939.6

18.2

1568.1

28

496.0462

836.25

27.114

1390.7

21

859.3

[20]

**Modification**

**Tensile** 

**Tensile** 

**Flexural** 

**Flexural** 

**Hardness**

**Impact** 

**References**

**strength** 

**(J/m2**

**)**

**modulus** 

**(MPa)**

**strength** 

**(MPa)**

**modulus** 

**(MPa)**

**strength** 

**(MPa)**

21

189

—

—

—

6.8

[33]
