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

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


## **Table 4.**

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

ethylene-propylene copolymer enhanced the interaction between the polymers and resilience, thereby improving the mechanical properties of the LDPE/PP composites. The use of compatibilizer in virgin and recycled polyolefins influenced the quality of the composites based on technology and recycled waste of LDPE by the addition of EPDM compatibilizer [41]. The presence of ethylene-propylene diene monomer (EPDM) revealed the variation in properties such as wide-angle x-ray diffraction (WAXD), differential scanning calorimetry (DSC), and mechanical properties of virgin and recycled LDPE/PP [36]. The destruction of thermal and mechanical properties of virgin LDPE and PP as well as blended LDPE/PP was found to be greater than those from recycled polyolefins because of the absence of antiaging in the virgin products. The impact EPDM modifier have been reported on stability of LDPE/PP products based on natural and influenced ageing conditions with improved mechanical (tensile and impact strength) properties of the LDPE/ PP with increase in modifier content. The impact EPDM modifier significantly improved the compatibility of recycled LDPE and PP and reduces the recrystallization of PP in the blends during aging and decreases the formation of the imperfect β polymorph crystal which depends on the presence of additives resulting in chain mobility retardation, presence of shear stress changing the chain structures, and fast cooling conditions at foil production as reported by Borovanska et al. [36]. Moreover, the significant improvement in rheological property such as viscosity, crystallinity index, and tensile properties of the recycled LDPE can be achieved by linear low-density polyethylene (LLDPE) blend with a ratio of 4:1 and applicably good for film products at 60% blended LLDPE [15]. The modification of recycled LDPE by PP using injection molding machine was also reported that the tensile properties increases with reduction in impact strength as increase in PP content as well as reduced processing temperature [42].

The effect of wood flour of *Pinus radiata* as fillers at a constant loading of 45 wt.% of recycled post-consumed plastic waste reported to be influenced by virgin PP [43]. In the report, the addition of virgin PP improved tensile and flexural moduli and flexural strength of wood plastic/LDPE composites (WPC). The highest mechanical properties of recycled LDPE composites have been reported for wood polymer composites with virgin PP (5%) and lower mechanical properties with higher virgin PP content of 55 and 71.5% compared to PE. The moisture absorption of WPC with virgin PP blend reported to be higher than without PP with adverse effect on the mechanical properties when immersed in water. More so, the use of virgin PP delay degradation and lower the thermal stability of WPC. This is also stay in agreement with report of Zhao et al. [44]. The decrease in tensile strength with increasing starch content in starch/LDPE composites attributed to incompatibility of the hydrophobic LDPE and hydrophilic starch and the increase in stiffness attributed to better dispersion of starch in LDPE matrix [45]. This incompatibility demands the use of compatibilizers such as styrene/ethylene-co-butylene/styrene grafted with maleic anhydride (SEBS-g-MA) and anhydride grafted polypropylene (PP-g-MA), Mixture Irganox 1098/Irganox 1078-Irgafos 168/Chimassorb 944 [44, 46].

The novel application of natural materials (filler or fibers) is to enhance undesirable properties and poor biodegradation of LDPE matrix. The use of rice husk, bambara, and mahogany fillers with improved tensile strength and modulus, flexural strength and modulus, and hardness with reduction in impact strength has been reported [47–49]. The increase in mechanical, thermal, and biodegradation behaviors of the composites was attributed to improved interfacial adhesion and compatibility. The reduction in impact strength is a result of fiber dispersion, uneven distribution, and micropore formation in the composites. It can be deduced that natural fillers or fibers contain a compatibilizer which has not been identified. There is also limited report on the modifications of fillers and fibers for enhancement of mechanical,

**61**

*Thermoplastic Recycling: Properties, Modifications, and Applications*

branching, dimensions, and types of polymeric chains [37].

interaction which can be modified by surface techniques.

physical (water absorption, density, etc.), thermal, and electrical properties (conductivity, dielectric properties, etc.) of LDPE matrix. Chemical recycling (pyrolysis) had been a major technology for waste or postconsumer LDPE to save the environment, but not cost-effective; emissions of some constituents and required additives or modifiers (catalysts) for considerable yields of the products in many applications [24, 30]. Incorporation of natural zeolite, clinoptilolite ((K2,Na2,Ca)Al6Si3072), improved the strength of the filled composites, rheological behavior, thermal, compatibility of the individual polymeric components, morphology, and texture of the moldings from recycled polyolefins which strongly depends on the type of zeolite, size and shape,

Chemical materials have been used as catalysts in the pyrolysis of plastics to obtain liquid products with higher yield and selectivity. Hence, numerous experiments were performed to find out the best catalyst to produce the most desirable products, taking the economic factor into consideration. Pyrolysis of plastic waste to fuel involves many limitations that prohibit the industrial plastic recycling process including the difficulty in modifying it from batch process to continuous process. In industrial process, plastic waste is fed into the reactor directly through hopper for melting in pyrolysis reactor with high melting point (300°C and above, depending on the types of plastic). Therefore, any temperature lower than its meting point may result to solidification of the plastics in the process pipelines, hence

**2.3 Modifications and properties of recycling of virgin and waste PVC**

The increase in commercial vehicles and road usage with construction resulted to increase in demand of bitumen for pavement and road construction. Yet, the durability of the bitumen depends on appropriate binder for enhancement of performance of bitumen. The use of little quantity of virgin thermoplastics provides a reasonable performance with bitumen but is uneconomical compared with only bitumen. The utilization of waste PVC for effective performance as bitumen binder in pavement and road construction products seems to be interesting because of its low cost and because it is one of the abundant thermoplastics that causes environmental threat [50]. The applications of PVC have been reported to hinder and be not suitable for many applications because of incompatibility as a result of many factors [51]. PVC possesses high melting points which hindered the mixing, and it is impractical to make any further attempts to incorporate it in some applications like bitumen road construction. Recycled LDPE/PVC blends have been modified using EPDM as effective toughening, compatibilizer, and dispersant agent in applications. Recyclability of PVC waste can be achieved mechanically without modifications or use of new plasticizer since the separation of other mixed plastics is possible through triboelectrostatic technology [50, 52]. The technology of triboelectrostatics depends on the ability of polymer to the electron loses or gains because electrons gains and charges negatively may be as a result of higher affinity of polymers, whereas loss of electrons and positively charge may be attributed to polymer with the lower affinity. Because of high electronegativity of chloride ions, it can mix with many polymers such as PET, PP, PS, and PE with enhanced properties as reported by Hamad et al. [50]. The use of wood fillers or fibers as natural modifiers have been reported to improve mechanical properties of recycled PCV rather the recyclability [53], and slightly reduction in mechanical (tensile, flexural, hardness and impact) and structural properties (i.e., decrease in molecular weight due to molecular chain scission caused by shear stress involved in reprocessing) [54]. The reduction in properties exists because of incompatibility or poor intermolecular

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

causing blockage of the pipelines.

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

*Thermosoftening Plastics*

well as reduced processing temperature [42].

ethylene-propylene copolymer enhanced the interaction between the polymers and resilience, thereby improving the mechanical properties of the LDPE/PP composites. The use of compatibilizer in virgin and recycled polyolefins influenced the quality of the composites based on technology and recycled waste of LDPE by the addition of EPDM compatibilizer [41]. The presence of ethylene-propylene diene monomer (EPDM) revealed the variation in properties such as wide-angle x-ray diffraction (WAXD), differential scanning calorimetry (DSC), and mechanical properties of virgin and recycled LDPE/PP [36]. The destruction of thermal and mechanical properties of virgin LDPE and PP as well as blended LDPE/PP was found to be greater than those from recycled polyolefins because of the absence of antiaging in the virgin products. The impact EPDM modifier have been reported on stability of LDPE/PP products based on natural and influenced ageing conditions with improved mechanical (tensile and impact strength) properties of the LDPE/ PP with increase in modifier content. The impact EPDM modifier significantly improved the compatibility of recycled LDPE and PP and reduces the recrystallization of PP in the blends during aging and decreases the formation of the imperfect β polymorph crystal which depends on the presence of additives resulting in chain mobility retardation, presence of shear stress changing the chain structures, and fast cooling conditions at foil production as reported by Borovanska et al. [36]. Moreover, the significant improvement in rheological property such as viscosity, crystallinity index, and tensile properties of the recycled LDPE can be achieved by linear low-density polyethylene (LLDPE) blend with a ratio of 4:1 and applicably good for film products at 60% blended LLDPE [15]. The modification of recycled LDPE by PP using injection molding machine was also reported that the tensile properties increases with reduction in impact strength as increase in PP content as

The effect of wood flour of *Pinus radiata* as fillers at a constant loading of 45 wt.% of recycled post-consumed plastic waste reported to be influenced by virgin PP [43]. In the report, the addition of virgin PP improved tensile and flexural moduli and flexural strength of wood plastic/LDPE composites (WPC). The highest mechanical properties of recycled LDPE composites have been reported for wood polymer composites with virgin PP (5%) and lower mechanical properties with higher virgin PP content of 55 and 71.5% compared to PE. The moisture absorption of WPC with virgin PP blend reported to be higher than without PP with adverse effect on the mechanical properties when immersed in water. More so, the use of virgin PP delay degradation and lower the thermal stability of WPC. This is also stay in agreement with report of Zhao et al. [44]. The decrease in tensile strength with increasing starch content in starch/LDPE composites attributed to incompatibility of the hydrophobic LDPE and hydrophilic starch and the increase in stiffness attributed to better dispersion of starch in LDPE matrix [45]. This incompatibility demands the use of compatibilizers such as styrene/ethylene-co-butylene/styrene grafted with maleic anhydride (SEBS-g-MA) and anhydride grafted polypropylene (PP-g-MA),

Mixture Irganox 1098/Irganox 1078-Irgafos 168/Chimassorb 944 [44, 46].

The novel application of natural materials (filler or fibers) is to enhance undesirable properties and poor biodegradation of LDPE matrix. The use of rice husk, bambara, and mahogany fillers with improved tensile strength and modulus, flexural strength and modulus, and hardness with reduction in impact strength has been reported [47–49]. The increase in mechanical, thermal, and biodegradation behaviors of the composites was attributed to improved interfacial adhesion and compatibility. The reduction in impact strength is a result of fiber dispersion, uneven distribution, and micropore formation in the composites. It can be deduced that natural fillers or fibers contain a compatibilizer which has not been identified. There is also limited report on the modifications of fillers and fibers for enhancement of mechanical,

**60**

physical (water absorption, density, etc.), thermal, and electrical properties (conductivity, dielectric properties, etc.) of LDPE matrix. Chemical recycling (pyrolysis) had been a major technology for waste or postconsumer LDPE to save the environment, but not cost-effective; emissions of some constituents and required additives or modifiers (catalysts) for considerable yields of the products in many applications [24, 30]. Incorporation of natural zeolite, clinoptilolite ((K2,Na2,Ca)Al6Si3072), improved the strength of the filled composites, rheological behavior, thermal, compatibility of the individual polymeric components, morphology, and texture of the moldings from recycled polyolefins which strongly depends on the type of zeolite, size and shape, branching, dimensions, and types of polymeric chains [37].

Chemical materials have been used as catalysts in the pyrolysis of plastics to obtain liquid products with higher yield and selectivity. Hence, numerous experiments were performed to find out the best catalyst to produce the most desirable products, taking the economic factor into consideration. Pyrolysis of plastic waste to fuel involves many limitations that prohibit the industrial plastic recycling process including the difficulty in modifying it from batch process to continuous process. In industrial process, plastic waste is fed into the reactor directly through hopper for melting in pyrolysis reactor with high melting point (300°C and above, depending on the types of plastic). Therefore, any temperature lower than its meting point may result to solidification of the plastics in the process pipelines, hence causing blockage of the pipelines.
