**4. PLA bioplastics**

PLA is one of the most studied bioplastics due to its recyclability and attractive specifications. PLA can be biodegraded under certain conditions, such as the presence of oxygen and moisture [59]. Moreover, PLA is a biodegradable material, and its usage within the biodegradable polymers has a high level of importance, because it significantly reduces the negative environmental impacts of wastes due to its biodegradability, improves the material recyclability, and eases monitoring external effects on the properties of the final composition. In this matter, the first reason is that the generation of wastes from industrial processes where the grinding process of the offcuts and blending with the neat polymeric matrix is integrated is unavoidable [60]. The second reason is the possibility of PLA wastes to be reused and recycled, because it is necessary to extend the lifetime service of PLA prior to discarding them into the biodisposal sites (i.e., composting sites) [61, 62]. Finally, the negligible environmental impacts of PLA could be ignored if it is not being possible for industries to recycle the obtained wastes [60].

In a work by Ohya et al. [63], they reported a procedure to develop graft polymerization of PLA on polysaccharides via TMS-protected polysaccharides. Based on their study, introduction of TMS protecting groups to chlorotrimethylsilane/ pyridine can make the low molecular weight polysaccharides soluble in organic solvents and lead to an approach which can control the overall amount of initiating groups (i.e., the overall amount of graft chains). Moreover, via usage of trimethylsilyl protection method, PLA-grafted polysaccharides with variable lengths and number of graft chains were developed. The graft copolymer films present lower glass transition temperature (Tg), crystallinity, melting temperature, and higher viscosity than pure PLA film. What is more, the usefulness of graft copolymer as a plasticizer was investigated with 1:4 blend films prepared from the graft copolymers and PLA. The blend films showed lower Tg and crystallinity and higher viscosity than pure PLA film [64].

In another research, multiple extrusions of PLA up to ten times were investigated by Enkiewicz et al. [61] using a double screw extruder for granulation of PLA followed by laboratory injection molding press, for preparation of specimens. In this case, their obtained results showed that the tensile strength values of PLA did not significantly depend on the number of extrusion cycles, and they showed only a little diversity from each other, showing a slight total reduction of about 5.2% after ten extrusion processes (**Figure 1(a)**). Besides, a negligible decrease in the tensile strain was observed (about 2.2–2.4%) which did not depend on the number of extrusion process. On the other hand, by an increase in the number of preformed

### **Figure 1.**

*(a) Tensile strength (*σ*M) and tensile stress at break (*σ*B) as functions of the extrusion number [61] and (b) zero viscosity of PLA as a function of injection number [60].*

**101**

acid can be seen.

*Development of Efficient Composites via Renewable, Recyclable, and Degradable Additives*

extrusions, the impact strength clearly declined (20.2% after ten extrusion processes), while the melt flow rate (MFR), water vapor, and oxygen transmission rates were significantly increased. The MFR value of the specimen subjected to ten extrusion processes was threefold higher than the original specimen. The thermal characteristics of specimens showed a slight decrease in the thermal stability of PLA, lower cold crystallization temperature, and a slight reduction in the melting point by increasing the number of cycles without any effect on the glass transition

PLA degradation has been found to be dependent on several factors, including molecular weight, purity, crystallinity, temperature, pH, the presence of terminal carboxyl or hydroxyl groups, water permeability, and additives all of which acting catalytically that may include enzymes, bacteria, or inorganic fillers [65]. Pyrolysis is a method which can lead to the treatment of polylactide, in which applied heat to a condensed substrate can lead to its chemical decomposition. Co-pyrolytic methods attracted considerable attention toward themselves due to their presented alternatives for disposal and convert wastes original form into valuable fuel sources. Likewise, the specific benefit of this procedure could be attributed to its potential for reduction of wastes within the nature, recovery of used chemical compounds, and replacing the developed fuel with frequently used fossil fuels. Furthermore, co-pyrolysis treatment of PLA-derived materials and biomass offers a potential alternative way for removal of wastes from the nature and could act as an upgrading approach during the pyrolysis of biomass and wastes [66]. PLA can be recycled to its primary form (i.e., monomer) through hydrolyze by boiling water or steam of lactic acid. This approach could lead to molecular recycling and provide an alternative for recycling both fabricated plant materials and post-consumed packages. In this regard, PLA could be hydrolyzed to its primary form by applying heat at 180–350°C for 30min, which can lead to recycle of L-lactic acid as the final

In a research by De Jong et al. [67], they depolymerized PLA through the release

of dimers in alkaline conditions, in which the end chain degradation could be explained via intramolecular transesterifications. In this matter, an electrophilic attack which is catalyzed via the base of the hydroxyl (OH<sup>−</sup>) end group on the second carbonyl group can lead to the formation of a ring and shorten the polymeric chain by hydrolysis of the final lactide. In the next step, free lactide hydrolysis into two lactic acid molecules. During this step, a random alkaline attacks to the carbon atoms of the ester groups, followed by the hydrolysis of the ester bond which leads to the intramolecular degradation of the primary chemical compound. Thereby, new low molecular weight molecules are produced; however, in the acidic conditions, the protonation process of the hydroxyl end group leads to an intramolecular hydrogen bond. The hydrolysis of the ester group can decrease the degree of polymerization of PLA due to the release of lactic acid molecules. Besides, random intramolecular protonation of ester groups' carbon atoms condenses the hydrolysis of ester bonds and produces diverse kinds of low molecular weight fragments [46]. Another study [60] on the reprocessing of PLA (containing 92% L-lactide and 8% D-lactide) showed that only the tensile modulus remains constant with thermomechanical cycles of up to seven injection moldings. Moreover, stress and strain at break, modulus, hardness, and rheological factors generally showed a small decline. Additionally, the viscosity of PLA decreased greatly (from 3960 to 713 Pa.s) after only one injection cycle. Zero viscosity (g0) of PLA as a function of injection number is presented in **Figure 1(b)**. The mechanical properties of the recycled PLA had become too poor for an industrial application of the polymer [14]. In **Table 3**, a list of starchy and cellulosic materials that were used for the production of lactic

*DOI: http://dx.doi.org/10.5772/intechopen.84560*

temperature (Tg) [61, 64].

outcome [66].

### *Development of Efficient Composites via Renewable, Recyclable, and Degradable Additives DOI: http://dx.doi.org/10.5772/intechopen.84560*

extrusions, the impact strength clearly declined (20.2% after ten extrusion processes), while the melt flow rate (MFR), water vapor, and oxygen transmission rates were significantly increased. The MFR value of the specimen subjected to ten extrusion processes was threefold higher than the original specimen. The thermal characteristics of specimens showed a slight decrease in the thermal stability of PLA, lower cold crystallization temperature, and a slight reduction in the melting point by increasing the number of cycles without any effect on the glass transition temperature (Tg) [61, 64].

PLA degradation has been found to be dependent on several factors, including molecular weight, purity, crystallinity, temperature, pH, the presence of terminal carboxyl or hydroxyl groups, water permeability, and additives all of which acting catalytically that may include enzymes, bacteria, or inorganic fillers [65]. Pyrolysis is a method which can lead to the treatment of polylactide, in which applied heat to a condensed substrate can lead to its chemical decomposition. Co-pyrolytic methods attracted considerable attention toward themselves due to their presented alternatives for disposal and convert wastes original form into valuable fuel sources. Likewise, the specific benefit of this procedure could be attributed to its potential for reduction of wastes within the nature, recovery of used chemical compounds, and replacing the developed fuel with frequently used fossil fuels. Furthermore, co-pyrolysis treatment of PLA-derived materials and biomass offers a potential alternative way for removal of wastes from the nature and could act as an upgrading approach during the pyrolysis of biomass and wastes [66]. PLA can be recycled to its primary form (i.e., monomer) through hydrolyze by boiling water or steam of lactic acid. This approach could lead to molecular recycling and provide an alternative for recycling both fabricated plant materials and post-consumed packages. In this regard, PLA could be hydrolyzed to its primary form by applying heat at 180–350°C for 30min, which can lead to recycle of L-lactic acid as the final outcome [66].

In a research by De Jong et al. [67], they depolymerized PLA through the release of dimers in alkaline conditions, in which the end chain degradation could be explained via intramolecular transesterifications. In this matter, an electrophilic attack which is catalyzed via the base of the hydroxyl (OH<sup>−</sup>) end group on the second carbonyl group can lead to the formation of a ring and shorten the polymeric chain by hydrolysis of the final lactide. In the next step, free lactide hydrolysis into two lactic acid molecules. During this step, a random alkaline attacks to the carbon atoms of the ester groups, followed by the hydrolysis of the ester bond which leads to the intramolecular degradation of the primary chemical compound. Thereby, new low molecular weight molecules are produced; however, in the acidic conditions, the protonation process of the hydroxyl end group leads to an intramolecular hydrogen bond. The hydrolysis of the ester group can decrease the degree of polymerization of PLA due to the release of lactic acid molecules. Besides, random intramolecular protonation of ester groups' carbon atoms condenses the hydrolysis of ester bonds and produces diverse kinds of low molecular weight fragments [46]. Another study [60] on the reprocessing of PLA (containing 92% L-lactide and 8% D-lactide) showed that only the tensile modulus remains constant with thermomechanical cycles of up to seven injection moldings. Moreover, stress and strain at break, modulus, hardness, and rheological factors generally showed a small decline. Additionally, the viscosity of PLA decreased greatly (from 3960 to 713 Pa.s) after only one injection cycle. Zero viscosity (g0) of PLA as a function of injection number is presented in **Figure 1(b)**. The mechanical properties of the recycled PLA had become too poor for an industrial application of the polymer [14]. In **Table 3**, a list of starchy and cellulosic materials that were used for the production of lactic acid can be seen.

*Renewable and Sustainable Composites*

PLA is one of the most studied bioplastics due to its recyclability and attractive specifications. PLA can be biodegraded under certain conditions, such as the presence of oxygen and moisture [59]. Moreover, PLA is a biodegradable material, and its usage within the biodegradable polymers has a high level of importance, because it significantly reduces the negative environmental impacts of wastes due to its biodegradability, improves the material recyclability, and eases monitoring external effects on the properties of the final composition. In this matter, the first reason is that the generation of wastes from industrial processes where the grinding process of the offcuts and blending with the neat polymeric matrix is integrated is unavoidable [60]. The second reason is the possibility of PLA wastes to be reused and recycled, because it is necessary to extend the lifetime service of PLA prior to discarding them into the biodisposal sites (i.e., composting sites) [61, 62]. Finally, the negligible environmental impacts of PLA could be ignored if it is not being

In a work by Ohya et al. [63], they reported a procedure to develop graft polymerization of PLA on polysaccharides via TMS-protected polysaccharides. Based on their study, introduction of TMS protecting groups to chlorotrimethylsilane/ pyridine can make the low molecular weight polysaccharides soluble in organic solvents and lead to an approach which can control the overall amount of initiating groups (i.e., the overall amount of graft chains). Moreover, via usage of trimethylsilyl protection method, PLA-grafted polysaccharides with variable lengths and number of graft chains were developed. The graft copolymer films present lower glass transition temperature (Tg), crystallinity, melting temperature, and higher viscosity than pure PLA film. What is more, the usefulness of graft copolymer as a plasticizer was investigated with 1:4 blend films prepared from the graft copolymers and PLA. The blend films showed lower Tg and crystallinity and higher viscosity than

In another research, multiple extrusions of PLA up to ten times were investigated by Enkiewicz et al. [61] using a double screw extruder for granulation of PLA followed by laboratory injection molding press, for preparation of specimens. In this case, their obtained results showed that the tensile strength values of PLA did not significantly depend on the number of extrusion cycles, and they showed only a little diversity from each other, showing a slight total reduction of about 5.2% after ten extrusion processes (**Figure 1(a)**). Besides, a negligible decrease in the tensile strain was observed (about 2.2–2.4%) which did not depend on the number of extrusion process. On the other hand, by an increase in the number of preformed

*(a) Tensile strength (*σ*M) and tensile stress at break (*σ*B) as functions of the extrusion number [61] and* 

*(b) zero viscosity of PLA as a function of injection number [60].*

possible for industries to recycle the obtained wastes [60].

**4. PLA bioplastics**

pure PLA film [64].

**100**

**Figure 1.**


**Table 3.**

*Starchy and cellulosic materials used for the production of lactic acid [46].*
