Inducing Rapid Crystallization of Slowly-crystallizable Copolyester by in situ Generation of Crystalline Nuclei in Melt of Copolyester

Abstract

KEY WORDS: Polymer Blend / Nucleating Agent / Poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) / Recently bacterial poly(3-hydroxybutyrate) (P(3HB)) has attracted much attention due to its inherent biodegradability. However, its brittleness and narrow processing temperature window limit its application. To overcome the inferior properties of P(3HB), a variety of P(3HB) copolymers such as, poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (P(3HB-co-3HV)) and poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (P(3HB-co-3HH)), have been bacterially synthesized.1 Especially, P(3HB-co-3HH)s with 3HH unit content of about 10-20 mol % have good mechanical properties.2 But the crystallization rate of P(3HB-co-3HH) compared with that of P(3HB) is too slow to use as molded products.In general, the addition of nucleating agents may be an effective method for acceleration of the crystallization of crystallizable polymers and the increase of the nucleation density, resulting in the reduction of the spherulite size. Boron nitride (BN) was found to be effective as the nucleating agent for the crystallization of P(3HB) and P(3HB-co-3HV). 3,4 But, it is found to be ineffective for P(3HB-co-3HH)s with relatively high 3HH unit content, as mentioned later in this article. Thus, it is in need of development of novel nucleating method effective for the crystallization of P(3HB-co-3HH)s.It is known that P(3HB-co-3HH) with 3HH composition higher than about 20 mol % is partially miscible with P(3HB) in the amorphous phase. 5As bacterially synthesized P(3HB) is a completely isotactic stereoregular polyester, it has higher tendency to crystallize than the 3HB-containing copolyesters.6 Bacterial P(3HB-co-3HH)s with high 3HB unit content form P(3HB) homopolymer type crystal, although the crystallization is very slow.7 In this study, we studied rapid crystallization of P(3HB-co-3HH) induced by in situ generated crystalline nuclei. EXPERIMENTALBacterial P(3HB-co-3HH) with 3HH unit content 18 mol % [P(3HB-co-18 mol %3HH)] was kindly supplied by Kaneka Corporation, Osaka, Japan.8 Because the comonomer-unit compositional distribution of bacterial P(3HB-co-18 mol %3HH) is very wide, as-produced P(3HB-co-18 mol %3HH) was fractionated with a chloroform(solvent)/n-heptane-(nonsolvent) mixed solvent systems at ambient temperature. 8 In this study, one of fractions with narrow comonomer-unit compositional distribution, that is, P(3HB-co-21 mol %3HH) (M n ¼ 1:15 Â 10 5 , M w =M n ¼ 1:42) was used. Bacterial P(3HB) sample (M n ¼ 1:55 Â 10 5 , M w =M n ¼ 2:56) provided by PHB Industrial S/A (Brazil) was used after purification. The BN fine powder was purchased from Nacalai Tesque, Inc (Kyoto, Japan). BN is known as nucleating agent for P(3HB). 9 The films of P(3HB-co-21 mol %3HH), P(3HB-co-21 mol %3HH)/P(3HB) (90 wt %/10 wt %) blend, P(3HB-co-21 mol %3HH)/BN (98 wt %/2 wt %) blend, P(3HB-co-21 mol %3HH)/P(3HB)/BN (88 wt %/10 wt %/2 wt %) blend (ternary blend), P(3HB) and P(3HB)/BN (98 wt %/2 wt %) blend were prepared by solution casting from chloroform solutions. The...

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

“…It is reasonable to think that orotic acid could establish some interactions (hydrogen bonds) with the polymer, and thus be less affected by the increasing of the HH unit content than BN. As it was found in our previous study for BN,44 ternary blends containing PHB and orotic acid could also be an effective way to nucleate P(HB‐ co ‐HH) copolymers with high HH contents.…”

“…As it was found in our previous study for BN, 44 ternary blends containing PHB and orotic acid could also be an effective way to nucleate P(HB-co-HH) copolymers with high HH contents.…”

“…In our recent studies, 44 it has been shown that PHBHH could be successfully nucleated by using ternary blends of the following composition: PHB (10 wt %), P(HB-co-21%HH) (88 wt %) and BN (2 wt %). In that case, it is believed that during the cooling process, BN particles induce a fast and selective crystallization of PHB, which will promote the fast crystallization of the P(HB-co-HH) copolymer.…”

Structure–Property Relationship in Melt-Spun Poly(hydroxybutyrate-co-3-hexanoate) Monofilaments

“…The mole percentage of the 3-HH unit has a prominent effect on thermal properties, such as melting temperature or heat of fusion [ 8 , 9 ]. The structural properties of PHBH, like its crystallization behavior, and the effect of aging on the mechanical properties of PHBH, containing different amounts of 3-HH, have been investigated in the past [ 10 , 11 , 12 , 13 ]. A high mole percentage of the 3-HH unit leads to lower melting temperatures, lower crystallinities, and reduced storage modulus and overall strength.…”

Crystallization of poly(3‐hydroxybutyrate‐ co ‐3‐hydroxyhexanoate) during melt extrusion promoted by residual crystals

“…For PHBH, the crystallization speed increases upon addition of higher‐melting PHAs such as PHB . In addition, mixtures of PHB and inorganic nucleating agents or the formation of an inclusion complex between PHB and cyclodextrin have been reported to be effective . Experiments performed under static conditions (eg, differential scanning calorimetry [DSC]) show that the resin melting temperature and crystalline memory (ie, a certain degree of regularity in the melted ingredients) are very important parameters for the crystallization and molding of PHBH…”