Plasticization of poly(3‐hydroxybutyrate) with triethyl citrate: Thermal and mechanical properties, morphology, and kinetics of crystallization

Abstract

Poly(3-hydroxybutyrate) (PHB), is one important biopolymer and a promising alternative to petroleum-based plastics. In this article, formulations of PHB and triethyl citrate (TEC) as plasticizer were prepared by melt extrusion. The effect of TEC on the mechanical, thermal, and morphological properties of PHB was investigated by tensile tests, impact resistance, dynamic-mechanical analysis, differential scanning calorimetry, polarized optical microscopy, and small-and wide-angle X-ray scattering. TEC acted as an efficient plasticizer for PHB, imparting gradual changes in the properties as the mass fraction of TEC increased. A reduction in the elastic modulus, an increase in the intensity of β relaxation indicated a higher capacity of mechanical energy dissipation for the formulations containing higher mass fractions of TEC. TEC reduced its glass transition and melting temperatures, contributing to the increase of the processing window of the temperature and minimizing thermal degradation of PHB. TEC had a strong influence on the kinetics of crystallization, the morphology of the spherulites, and the crystalline structural parameters, such as long period, crystalline lamella, and interlamellar amorphous region thicknesses. Our study clarifies how the morphology of the PHB crystalline phase evolves in the presence of the plasticizer and with the time of crystallization.

Plasticization of Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) with an Oligomeric Polyester: Miscibility and Effect of the Microstructure and Plasticizer Distribution on Thermal and Mechanical Properties

“…This effect combined with the suitable processing conditions applied resulted in good melt-processing stability with minor chain degradation induced by the shear at high temperatures. A similar tendency (a decrease in the force before unloading and the modulus of the force decay rate as a function of the plasticizer content for formulations of PHB with TEC) was reported in our previous work . However, higher molar mass PHB ( M w = 394 kDa) was used, and the GPC analysis showed a higher decrease in the M w (around 11–16% for plasticized samples) and Đ values, indicating a preferential scission of long polymer chains during processing.…”

“…Compared to other oligomeric plasticizers, PLAP acts to decrease T g , T m , and the elastic modulus and to increase the elongation at break similarly to poly­[di­(ethylene glycol) adipate], poly­(caprolactone)-triol, Pluronic F68 and F127, Laprol 503 and 5003, TolonateXFLO100, and poly­(ethylene glycol) (PEG) with the molar mass in the range from 0.2 to 6.0 kDa. ,,,, For these plasticizers, a maximum decrease in T g of around 15 °C, T m in the range of 3–8 °C, the elastic modulus in the range from 35 to 60%, and an increase in the elongation at break lower than 10% have been reported. On the other hand, low molar mass plasticizers such as phthalates, citrates, ,, glycerol esters, ,, vegetable oils, , terpenes, and other esters ,,, are more effective in decreasing T g and T m and in tuning the mechanical properties of formulations when compared to the oligomeric plasticizers. Using low molar mass plasticizers, a decrease in the range of 20–40 °C in T g , around 10–20 °C in T m , and from 60 to 80% in the elastic modulus, and increase of the elongation at break of more than 10% are frequently reported.…”

“…A similar tendency (a decrease in the force before unloading and the modulus of the force decay rate as a function of the plasticizer content for formulations of PHB with TEC) was reported in our previous work. 75 However, higher molar mass PHB (M w = 394 kDa) was used, and the GPC analysis showed a higher decrease in the M w (around 11−16% for plasticized samples) and Đ values, indicating a preferential scission of long polymer chains during processing. A higher extent of PHB degradation (molar mass reduction of 34%) was reported by Garcia-Garcia et al 51 for the extrusion and injection molding of PHB (M w = 426 kDa) plasticized with epoxidized vegetable oils using similar processing conditions.…”

Developments of biobased plasticizers for compostable polymers in the green packaging applications: A review

“…This phenomenon was previously reported for PLA with ATBC 67 . The same team studied the effect of TEC on the mechanical and thermal properties of PHB 81 . The elastic modulus and melting temperature of PHB were reduced.…”

“…CAPs derivatives are widely used as eco‐friendly plasticizers in various applications including biodegradable polymers food additives 50 . For food contact films various types of commercial CAPs such as TEC, TBC, ATEC, and ATBC were used for compostable polymers including PLA, 62,66–75 PHAs, 31,68,76–81 cellulose acetate, 82–84 PCL, 85 PBS, 66 and starch 86–88 …”