Effects of molecular weight and grafted maleic anhydride of functionalized polylactic acid used in reactive compatibilized binary and ternary blends of polylactic acid and thermoplastic cassava starch

Abstract

Polylactic acid (PLA) was reactively functionalized with maleic anhydride (MA) and 2,5-bis(tert-butylperoxy)22,5-dimethylhexane (Luperox 101 or L101) using a twin screw extruder (TSE). The effects of functionality (grafted MA level) and/or number average molecular weight of functionalized PLA (PLA-g-MA) as the reactive polymer pairs (binary blends) and reactive compatibilizer (ternary blends) were investigated. Due to the dominant side reaction during melt free radical grafting, polymer degradation or chain scission, PLA-g-MA having a higher grafted MA had lower molecular weights and intrinsic viscosity as well as broader molecular weight distribution values. The thermal, physical, mechanical, and morphological properties of binary blends produced by using the TSE and injection molding at a ratio of 70 wt % PLA-g-MA and 30 wt % thermoplastic cassava starch (TPCS) were analyzed. The reactive blends having grafted MA more than 0.4 wt % had poor tensile strength and elongation at break. Similar trends in morphology and tensile properties were observed in the reactive ternary blends. The use of PLA-g-MA strongly impacted the elongation at break but not the modulus or tensile strength. An increase of PLA-g-MA's number average molecular weight (M n or M n ) improved the tensile properties of the blends. The reactive ternary blend having 0.1 wt % grafted MA on PLA and PLA-g-MA basis and PLA-g-MA's M n of 45 kDa offered the highest elongation at break.

Improving the toughening in poly(lactic acid)‐thermoplastic cassava starch reactive blends

“…Blends of PLA and TPCS have been evaluated, and the biodegradable blends showed enhanced mechanical properties. Since PLA is a hydrophobic material and starch is a hydrophilic material, physical blends of PLA and TPS are considered immiscible, with poor interfacial adhesion .…”

“…Reactive blending of PLA with TPCS using a compatibilizer, such as maleic anhydride (MA), and different peroxide initiators, such as 2,5‐ bis ( tert ‐butylperoxy)‐2,5‐dimethylhexane (L101) and dicumyl peroxide (DCP), could improve interfacial adhesion and as a consequence the elongation at break. But reactive blending could also have side effects on the thermal properties and molecular structure . Several researchers reported the use of compatibilizers and peroxide initiators for production of reactive blends of PLA and TPS .…”

“…But reactive blending could also have side effects on the thermal properties and molecular structure . Several researchers reported the use of compatibilizers and peroxide initiators for production of reactive blends of PLA and TPS . MA is a common compatibilizer, extensively used for compatibilization of immiscible polymers .…”

“…Several approaches have been used to evaluate the reactive compatibilization of PLA and TPS blends but fewer with TPCS blends . Therefore, a detailed study of the production of reactive blends of PLA and TPCS with different initiators using common processing techniques is needed.…”

Microwave‐assisted green approach for graft copolymerization of l‐lactic acid onto starch

“…To overcome the immiscibility between starch and PLA, two main approaches have been reported: the use of compatibilizers as a bridge to binding (chemical or physical) between the PLA and starch rigid structure; or the plasticizing of starch granules to perform the penetration of L‐lactic acid functional groups and/or PLA chains into the amylose and amylopectin complex . These conventional modification methods, however, have been found to lead to some undesirable effects on final product properties such as causing full biodegradation., all of these conventional modification methods made some undesirable effects on the final product properties such as full biodegradation…”