Table 2.

Various natural additives used in polymers.

Matrix	Additive (content)	Mixing/Preparation Method	Role, Change in Properties/Observations	Ref.
Antibacterial/Antioxidant Plastics
PVC-based composites with self-sterilizing and antibacterial activity against S. aureus (functional antibacterial plastic).	Chitosan (wt % 0–40).	The mix was melt-compounded in an internal mixer at 150 °C.	Chitosan addition increased Young’s modulus evidencing a good CS–PVC interaction. Chitosan addition had no negative impact on thermal stability of the PVC composites which allows for possibility of producing composites by with thermo-mechanical processes, without risk of thermal decomposition.	[59]
Biodegradable polymer fiber nets of poly (lactic acid) (PLA)/poly (butylene adipateco-terephthalate) (PBAT) (60:40). Packaging material for fruit and vegetables preservation.	Pine essential oil (10%–20%). Some formulations were additionally coated with chitosan (1%).	Extruded biodegradable polymer.	With essential oil addition increased plasticity (at 10% Pine EO), elongation at break and decreased Young’s modulus. When chitosan was added as a coating, stiffening of the fiber was observed.	[142]
PLA-based composites for the packaging industry.	Water-soluble extracts (2%; 10%; 20%; 30%) from banana pseudo–stems.	Solution blending, casting and thermocompression.	Water-soluble extracts acted as a plasticizer on PLA (Tg decrease) and has slightly positive influence on its stiffness in the glassy state, whereas the drawability remained fairly acceptable when PLA-based materials where drawn at 75 °C above Tg.	[143]
Antimicrobial PLA films for food packaging with low silver release.	Alginate microbeads obtained by electrostatic extrusion (200 μm) with incorporated AgNPs (1.5 wt % Ag; 3 wt % alginate).	Solvent casting	PLA matrix acted as a diffusion barrier so that the released silver in water after 10 days was within the prescribed limit of 0.05 mg kg−1 while the films induced inhibitory effects against Staphylococcus aureus.	[144]
Poly caprolactone (PCL) nano fibrous mat with antioxidant activity for antimicrobial wound dressings.	Extract of medicinal plant Clerodendrum phlomidis.	Electrospinning	The plant extract conferred antibacterial activity and increased in wettability of the PCL fibers without affecting their mechanical properties.	[145]
Polyethylene oxide (PEO) These results will recommend these films a potential candidate in electrochemical and photoelectrical devices.	Starch (30 wt %) doped with various concentrations of gold nanoparticles (Au NPs)	Solvent casting	Differential scanning calorimetry (DSC) measurement indicated miscibility between the two polymers. Found electrical conductivity increased as Au NPs content increased. The miscibility between PEO and starch could be due to the oxygen atoms of PEO interacting through hydrogen H-bonds between the hydroxyl groups of starch. DSC revealed that the thermal stability of the blend polymer decreased after addition of the nanofiller.	[146]
Poly(lactic acid), PLA. The low cost and toxicological impact make cardanol a valid alternative to the plasticizer PEG.	Cardanol derived plasticizers (10%, 20% and 30%); three different plasticizers were used: neat cardanol, cardanol acetate (CA), and epoxidized cardanol acetate (ECA) were used, at contents ranging between 10% and 30%.	Mixing PLA, pre-dried at 70 °C for 24 h, and different amounts of plasticizers (10%, 20%, and 30%) for 15 min at 190 °C in a HAAKE RHEOMIX 600\610 mixer, with a rotor speed of 60 rpm.	PLA plasticized by cardanol derivatives showed lower modulus than PEG plasticized PLA. The tensile modulus of plasticized PLA was correlated to the evolution of glass transition temperature and degree of crystallinity. At low plasticizers content, the modulus of PLA decreased as the glass transition temperature decreased, due to a better miscibility of the plasticizer with PLA. The opposite occurred at high plasticizer content; in this case, the higher modulus found for more compatible plasticizers were attributed to an increased crystallization kinetic.	[147]
PU polyurethane 3D-printed foams as thermal insulation, sound absorption or as damping materials.	Cork powder (1%, 3%, and 5% wt/wt).	The TPU powder was mixed with cork powder (1%, 3%, and 5% wt/wt) in the Retsch cross beater mill SK1 without sieves. Afterwards, the mixtures were left over night in an oven at 105 °C to remove moisture. The mixtures were then extruded in a Felfil Evo Colours extruder using 4 rpm at 210 °C to produce the 3D printable filaments.	3D-printed PU polyurethane composite foams for thermal applications with enhanced mechanical properties. Due to the presence of cork as well as to the presence of voids the resulting foams presented lower density, lower thermal conductivity and proved to be more flexible. The stiffness of the ensuing composites was also reduced but the elastomeric behavior of the 3D-printed foams produced may find applications that combine thermal insulation with damping properties. Yet, the use of cork did not affect the thermal stability of the composites. Cork is a well-known low thermal conductive material, which can further reduce the thermal conductivity of PU foams Besides their thermal insulation properties, their elastomeric behavior suggests that the 3D-printed foams produced may be used as thermal insulation, sound absorption or as damping materials.	[148]
Polyethylene/poly (lactic acid)/Degradable polymeric films	Chitosan (15 wt %) with and without poly (ethylene-g-maleic anhydride) (PEgMA) as compatibilizer.	Laboratory mixer-extruder. 145 °C and 155 °C for the screw barrel.	Polyethylene/poly (lactic acid)/chitosan films, with and without poly (ethylene-g-maleic anhydride) (PEgMA) as compatibilizer, were prepared by extrusion. It was demonstrated that blends of synthetic and natural polymers have a higher susceptibility to degradation in comparison to neat polyethylene and poly (lactic acid) films. Additionally, it is found that the incorporation of PEgMA into the extruded films apparently favored the polymer degradation, as it deduced from the fall of the mechanical properties when the films are exposed to accelerated weathering simulation.	[149]