Effect of orotic acid as a nucleating agent on the crystallization of bacterial poly(3‐hydroxybutyrate‐co‐3‐hydroxyhexanoate) copolymers

Abstract

The kinetics of crystallization induced by orotic acid (OA) and boron nitride (BN) as nucleating agents were investigated for bacterial poly(3-hydroxybutyrate-co-3-hydroxyhexanoate)s (P(HB-co-HH)s) containing from 0 to 18% HH monomer units. The nucleation efficiency of these two chemicals was investigated by differential scanning calorimetry (DSC) and polarized optical microscopy (POM). It was found that both orotic acid and boron nitride are able to nucleate the crystallization of PHB. In the case of P(HB-co-HH) copolymers, orotic acid showed an outstanding nucleating effect. The comparison of half-crystallization times shows that for P(HB-co-10% HH), the crystallization initiated by orotic acid is more than three time faster than the one induced by boron nitride (t 1/2BN /t 1/2OA (60 C) ¼ 3.7 and t 1/2BN /t 1/2OA (90 C) ¼ 4.5). According to the fact that orotic acid is a biodegradable, biocompatible and a nontoxic chemical, this nucleating agent is a promising solution for PHAs used in medical applications such as implants.

Nucleation mechanism of polyhydroxybutyrate and poly(hydroxybutyrate‐co‐hydroxyhexanoate) crystallized by orotic acid as a nucleating agent

“…According to our POM (Polarized Optical Microscopy) observations reported in a previous work, 5 orotic acid is not dissolve in PHB and PHB10HH melts during the preparation of the sample (2 min at 190 C), nevertheless unnoticeable dissolution could happened on the nucleating agent crystal surface and lead to a chemical nucleation via the process described in Scheme 3. To identify this chemical mechanism, and to see if this mechanism is promoted by a thermal treatment, gel permeation chromatography (GPC) tests were carried out on both solvent cast and hot pressed sample.…”

“…Our previous work 5 showed that orotic acid, a green chemical (See chemical structure in Fig. 1 content (18%).…”

“…Similar studies showed that nucleation efficiency of boron nitride (BN), a more commonly used nucleating agent for many kinds of polymers, was strictly decreasing with the increasing of the HH monomer content of P(HB-co-HH). 5 For further understanding why orotic acid shows this outstanding nucleating ability, its nucleation mechanism on PHB and P(HB-co-HH) was investigated in this study.…”

Nucleation Effect of Layered Metal Phosphonate on Crystallization of Bacterial Poly[(3‐hydroxybutyrate)‐co‐(3‐hydroxyhexanoate)]

“…[15] By adding an NA, the crystallization rate of a polymer can be enhanced due to the increasing of the nucleation density and the decreasing of the spherulite size. So far, a number of chemicals have been introduced as NAs for PHAs including boron nitride (BN), [15][16][17] talc, [15,16] saccharin, [18] lignin, [19] orotic acid, [20] thymine, [17] melamine, [17] terbium oxide (Tb 2 O 3 ), [15] lanthanum oxide (La 2 O 3 ), [15] a-cyclodextrin, [21] uracil, [22] organophosphorus compounds, [23] and so forth.…”

Insight into the role of bound water of a nucleating agent in polymer nucleation: a comparative study of anhydrous and monohydrated orotic acid on crystallization of poly(l-lactic acid)

“…However, previous studies are mainly focused on the nucleation effects of monohydrated form. 34,42,43 To our best knowledge, the role of bound water of a hydrated NA and its phase stability and transitions during melt blending process in the nucleation effectiveness for PLLA crystallization are not involved and still unknown, although these understandings are of importance for regulating the crystallization kinetics and the nal physical properties of PLLA by reasonable use of orotic acid as an effective nucleating agent.…”