Effect of additives on the melt rheology and thermal degradation of poly[(R)‐3‐hydroxybutyric acid]

Abstract

Thermal degradation of poly[(R)23-hydroxybutyric acid] (PHB) during melt mixing results in random chain scission that produces shorter polymer chains containing crotonic and carboxyl end groups. One way of preventing this serious reduction of molar mass is to add agents that react with at least two of the newly generated end groups. Different types of commercially available additives known to react with carboxyl group, namely bis(3,4-epoxycyclohexylmethyl) adipate (BECMA), 2,2'-bis(2-oxazoline) (BOX), trimethylolpropane tris(2-methyl-1-aziridinepropionate) (PETAP), triphenyl phosphate (TPP), tris(nonylphenyl) phosphate (TNPP), polycarbodiimide (PCDI), and poly(methyl metharylate-co-glycidyl methacrylate) (GMA.MMA) were mixed with PHB by cocasting from solution in chloroform. Dynamic rheology as well as measurements of molar masses before and after dynamic analysis was used to evaluate the effect of the additives on the melt stability of PHB. Measurements of the dynamic shear modulus and the molar mass of molten PHB with the additives PCDI and GMA.MMA showed a minor improvement on the thermal stability. Furthermore, TPP and TNPP did not affect the thermal stability of PHB, whereas the presence of BECMA, BOX, and PETAP gave a strong decrease of the dynamic modulus compared with neat PHB.

Improvement of the compatibility between poly(3-hydroxybutyrate) and poly(ε-caprolactone) by reactive extrusion with dicumyl peroxide

“…Despite these interesting features, P3HB polymer chains are highly stereoregular and this gives highly crystalline polymers (with a degree of crystallinity over 55%). On the other hand, as its glass transition temperature (T g ) is located below the room temperature (typically around 0-2 ºC), P3HB undergoes physical aging related to secondary crystallization [5,6]. For this reason, P3HB is a highly fragile polymer with very low plastic deformation [7].…”

Improvement of Mechanical Ductile Properties of Poly(3-hydroxybutyrate) by Using Vegetable Oil Derivatives

“…It is a crystalline thermoplastic aliphatic polyester that can be synthesized from different bacteria species as energy reserves . P3HB offers a high melt temperature in the 175–180 °C range and a high crystallinity that can be higher than 55% . Additionally, it degrades to carbon dioxide and water by natural microbial mineralization .…”

“…Temperatures over 190 °C as well as high residence time give rise to a quick thermal degradation on P3HB . Thermal degradation of P3HB results in chain scission which leads to a rapid decrease in the molecular weight and this has a negative effect on its overall properties . On the other hand, one important drawback of P3HB is its high stiffness which results in a high fragile polymer due to its high crystallinity .…”

Melt processability and thermomechanical properties of blends based on polyhydroxyalkanoates and poly(butylene adipate-co-terephthalate)

“…The modulus for the as-received and soxhlet extracted polymer decreased by approximately two decades over 40 min, respectively, due to thermal degradation that occurred at 170 C. The rheological properties can be related to the molecular weight, and a reduction in modulus to polymer chain scission reactions. 34 The effect of the pre-treatments on the melt shear storage modulus for P(3HB) was not obvious from the rheology measurements (ESI, Fig. S3a †).…”