Fully biodegradable blends of poly(butylene succinate) and poly(butylene carbonate): Miscibility, thermal properties, crystallization behavior and mechanical properties

Fully biodegradable poly(butylene succinate) (PBS) and poly(butylene carbonate) (PBC) blends were prepared by melt blending. Miscibility, thermal properties, crystallization behavior and mechanical properties of PBS/PBC blends were investigated by scanning electron microscopy (SEM), phase contrast optical microscopy (PCOM), differential scanning calorimetry (DSC), wide angle X-ray diffraction (WAXD) and mechanical properties tests. The SEM and PCOM results indicated that PBS was immiscible with PBC. The WAXD results showed that the crystal structures of both PBS and PBC were not changed by blending and the two components crystallized separately in the blends. The isothermal crystallization data showed that the crystallization rate of PBS increased with the increase of PBC content in the blends. The impact strength of PBS was improved significantly by blending with PBC. When the PBC content was 40%, the impact strength of PBS was increased by nearly 9 times.     

Performance of biodegradable microcapsules of poly(butylene succinate), poly(butylene succinate-co-adipate) and poly(butylene terephthalate-co-adipate) as drug encapsulation systems

Poly(butylene succinate) (PBSu), poly(butylene succinate-co-adipate) (PBSA) and poly(butylene terephthalate-co-adipate) (PBTA) microcapsules were prepared by the double emulsion/solvent evaporation method. The effect of polymer and poly(vinyl alcohol) (PVA) concentration on the microcapsule morphologies, drug encapsulation efficiency (EE) and drug loading (DL) of bovine serum albumin (BSA) and all-trans retinoic acid (atRA) were all investigated. As a result, the sizes of PBSu, PBSA and PBTA microcapsules were increased significantly by varying polymer concentrations from 6 to 9%. atRA was encapsulated into the microcapsules with an high level of approximately 95% EE. The highest EE and DL of BSA were observed at 1% polymer concentration in values of 60 and 37%, respectively. 4% PVA was found as the optimum concentration and resulted in 75% EE and 14% DL of BSA. The BSA release from the capsules of PBSA was the longest, with 10% release in the first day and a steady release of 17% until the end of day 28. The release of atRA from PBSu microcapsules showed a zero-order profile for 2 weeks, keeping a steady release rate during 4 weeks with a 9% cumulative release. Similarly, the PBSA microcapsules showed a prolonged and a steady release of atRA during 6 weeks with 12% release. In the case of PBTA microcapsules, after a burst release of 10% in the first day, showed a parabolic release profile of atRA during 42 days, releasing 36% of atRA.     

The crystallization behavior of biodegradable poly(butylene succinate) in the presence of organically modified clay with a wide range of loadings

The crystallization behavior of poly(butylene succinate)(PBS) nanocomposites with a wide range of contents of clays was revealed. It was of interest to find that the crystallization rate of PBS was accelerated obviously at relatively low contents of clays; while a retarded crystallization kinetics and a decreased crystallinity of PBS were found in the nanocomposites with higher clay contents. Two interplaying effects existed in the nanocomposites, i.e., a suppression effect of clays on nucleation and a templating effect of clays on crystal growth, were clarified to contribute to this intriguing crystallization behavior.     

Multiple melting behavior of poly(butylene succinate)

The multiple melting behavior of poly(butylenes succinate) (PBS) isothermally crystallized from the melt was investigated using differential scanning calorimetry (DSC), temperature modulated DSC (MDSC) and polarized optical microscopy. PBS exhibits at most four melting endotherms (denoted as T_m1, T_m2, T_m3, and T_m4 from high to low temperatures) and a crystallization exotherm (denoted as T_re) in the DSC heating trace. Multiple melting endotherms were observed even at high heating rates. The origins of each endothermal and exothermal peak were discussed in detail. It is suggested that: (i) the crystallization exothermic peak, T_re, relates to the recrystallization of the melt of the crystallites with lower thermal stability; (ii) the T_m1 is ascribed to the melting of crystallites formed through recrystallization; (iii) two crystal populations with different thermal stability are responsible for the T_m2 and T_m3; (iv) the T_m4, which is the annealing peak, represents the transition of the rigid amorphous fraction (RAF) from solid-like RAF into liquid-like amorphous fraction.     

Effects of crystallization temperature and blend ratio on the crystal structure of poly(butylene adipate) in the poly(butylene adipate)/poly(butylene succinate) blends

The effects of crystallization temperature and blend ratio on the polymorphic crystal structures of poly(butylene adipate)(PBA) in poly(butylene succinate)(PBS)/poly(butylene adipate)(PBS/PBA) blends were studied by means of differential scanning calorimetry(DSC), wide-angle X-ray diffraction(XRD) and atomic force microscopy(AFM). It was revealed that the polymorphism of PBA can be regulated by the blend ratio even in a non-isothermal crystallization process. The results demonstrate that high temperature favors flat-on α crystals, while low temperature contributes to edge-on β crystals. It was also found that the effect of blend ratio on the crystallization mechanism of PBA is well coincident with that of the crystallization temperature. The increment of PBS content in the PBS/PBA blend gives rise to more β-form crystals of PBA. For those PBS/PBA blends with low PBA content, the interlamellar phase segregation of PBA makes its molecular chains so difficult to diffuse from one isolated microdomain to another that high crystallization temperature and sufficiently long crystallization time will be required if the PBA α-type crystals are targeted.     

Transesterification and crystallization behavior of poly(butylene succinate)/poly(butylene terephthalate) block copolymers

The block copolymers of poly(butylene succinate) (PBS) and poly(butylene terephthalate) (PBT) were synthesized by melt processing for different times. The sequence distribution, thermal properties, and crystallization behavior were investigated over a wide range of compositions. For PBS/PBT block copolymers it was confirmed by statistical analysis from ¹H-NMR data that the degree of randomness (B) was below 1. The melting peak (T_m) gradually moved to lower temperature with increasing melt processing time. It can be seen that the transesterification between PBS and PBT leads to a random copolymer. From the X-ray diffraction diagrams, only the crystal structure of PBS appeared in the M1 copolymer (PBS 80 wt %) and that of PBT appeared in the M3 (PBS 50 wt %) to M5 (PBS 20 wt %) copolymers. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 147–156, 1998     

Thermal degradation mechanism of poly(ethylene succinate) and poly(butylene succinate): Comparative study

Two aliphatic polyesters that consisted from succinic acid, ethylene glycol and butylene glycol, —poly(ethylene succinate) (PESu) and poly(butylene succinate) (PBSu)—, were prepared by melt polycondensation process in a glass batch reactor. These polyesters were characterized by DSC, ¹H NMR and molecular weight distribution. Their number average molecular weight is almost identical in both polyesters, close to 7000 g/mol, as well as their carboxyl end groups (80 eq/10⁶ g). From TG and Differential TG (DTG) thermograms it was found that the decomposition step appears at a temperature 399 °C for PBSu and 413 °C for PESu. This is an indication that PESu is more stable than PBSu and that chemical structure plays an important role in the thermal decomposition process. In both polyesters degradation takes place in two stages, the first that corresponds to a very small mass loss, and the second at elevated temperatures being the main degradation stage. The two stages are attributed to different decomposition mechanisms as is verified from the values of activation energy determined with iso-conversional methods of Ozawa, Flyn, Wall and Friedman. The first mechanism that takes place at low temperatures, is auto-catalysis with activation energy E = 128 and E = 182 kJ/mol and reaction order n = 0.75 and 1.84 for PBSu and PESu, respectively. The second mechanism is nth-order reaction with E = 189 and 256 kJ/mol and reaction order n = 0.68 and 0.96 for PBSu and PESu, respectively, as they were calculated from the fitting of experimental results.     

Biodegradability of poly(butylene succinate) (PBS) composite reinforced with jute fibre

Poly(butylene succinate) (PBS)/jute composites were prepared, and the effects of fibre content, diameter, surface modification and arrangement forms on the biodegradability were evaluated by compost-soil burial test. The weight losses of PBS/jute composites are higher than that of pure PBS film and bulk jute fibre, and decreased with increasing fibre content. The weight loss of PBS/10% jute composite after 180 days is 62.5%. In the case of the effect of fibre diameter, the weight loss is found to decrease with decreasing fibre diameter. For the effect of fibre surface modification, the order of higher weight loss is PBS/untreated jute > PBS/alkali treated jute > PBS/coupling agent treated jute. Furthermore, the composite of PBS/woven fabric has the highest weigh loss, followed by that of PBS/nonwoven fabric and PBS/bulk jute fibre, respectively.     

Influence of transesterification reactions on the miscibility and thermal properties of poly(butylene/diethylene succinate) copolymers

Poly(butylene/diethylene succinate) block copolymers (PBSPDGS), prepared by reactive blending of the parent homopolymers (PBS and PDGS) in the presence of Ti(OBu)₄, were analyzed by ¹H-NMR, TGA and DSC, in order to investigate the effects of the transesterification reactions on the molecular structure and thermal properties. ¹H-NMR analysis evidenced the formation of copolymers whose degree of randomness increases with the mixing time. The thermal analysis of the melt-quenched samples showed that the melting peak, due to the crystalline phase of PBS, tends to disappear with increasing mixing time and therefore with decreasing the block length in the copolymers. As concern miscibility, a single homogeneous amorphous phase always occurred, independently on block length. Nevertheless, a phase separation, due to the tendency of the PBS blocks to crystallize, was evidenced in the copolymers with long butylene succinate sequences. The results obtained indicated that the block size had a fundamental role in determining the crystallizability and, therefore, phase behavior of the block copolymers.     

Effect of transesterification reactions on the crystallization behaviour and morphology of poly(butylene/diethylene succinate) block copolymers

The melting behaviour, the crystallization kinetics and the morphology of block poly(butylene/diethylene succinate) copolymers (PBSPDGS) were investigated by means of differential scanning calorimetry and hot stage optical microscopy. Multiple endotherms were evidenced in the PBSPDGS samples, due to melting and recrystallization processes, similarly to PBS. By applying the Hoffman-Weeks’ method, the of both the homopolymer and the copolymers was derived. The isothermal crystallization kinetics was analyzed according to the Avrami’s treatment. The copolymers with long PBS blocks are characterized by a very similar behaviour with respect to pure poly(butilene succinate), indicating that PBS macromolecular folding is not affected by the presence of non-crystallizable diethylene succinate blocks. On the contrary, the copolymers characterized by very short PBS block length were found to crystallize at a slower rate than the homopolymer. As a matter of fact, a higher value of the work of chain folding was also derived on the basis of Hoffman-Lauritzen nucleation theory. Anyway, in all cases the crystallization mechanism (heterogeneous nucleation and three-dimensional growth) was found to be the same.     

Effects of functionalized graphenes on the isothermal crystallization of poly(L-lactide) nanocomposites

The effects of graphene oxide(GO) with polar groups and functionalized GO(f GO) with nonpolar groups on the isothermal crystallization of poly(L-lactide)(PLLA) were compared. Functionalized GO was obtained by grafting octadecylamine and characterized by FTIR, WAXD and TGA. Isothermal crystallization kinetics of PLLA/GO and PLLA/f GO nanocomposites were investigated by combining DSC data and Avrami equation. The results showed that f GO could improve PLLA crystallization rate more obviously than GO. By analyzing the morphology obtained from POM, SEM and TEM, it was found f GO with large layer space dispersed better in PLLA and supplied more nucleation sites than GO. Therefore, for the multilayer graphene, increasing the layer spaces is important to improve its dispersion in polymers, which will cause the crystal kinetics changing of polymers.     

Morphology and properties of nanostructured materials based on polypropylene/poly(butylene succinate) blend and organoclay

Nanostructured materials based on organically modified montmorillonite (OMMT) and polypropylene (PP)/poly(butylene succinate) (PBS) blend were prepared via melt-mixing of PP, PBS, and OMMT in a batch mixer. The weight ratio of PP and PBS was 70:30, and the OMMT loading varied from 0.5 to 5 wt%. The surface morphologies of unmodified and OMMT-modified blend were studied by field-emission scanning electron microscopy. Results showed that the particle size of the dispersed PBS phase was significantly reduced with the addition of a small amount of OMMT (1.5 wt%). Upon the addition of 5 wt% of OMMT, the domain size of the dispersed PBS phase changed significantly from the unmodified blend, and a homogeneous dispersion of very fine particles of PBS was observed. The degree of dispersion of silicate layers in the blend matrix was characterized by X-ray diffraction and transmission electron microscopy. The improved adhesion between the phases and the fine morphology of the dispersed phase contributed to the significant improvement in the properties and thermal stability of the final nanocomposite materials. On the basis of these results, we describe a general understanding of how the morphology is related to the final properties of OMMT-incorporated PP/PBS blend.     

Biodegradability of bio-flour filled biodegradable poly(butylene succinate) bio-composites in natural and compost soil

This study investigated the biodegradability of PBS and bio-flour, which is a poly(butylene succinate) (PBS) bio-composite filled with rice-husk flour (RHF) reinforcing, in natural and aerobic compost soil. The percentage weight loss and the reduction in mechanical properties of PBS and the bio-composites in the compost soil burial test were significantly greater than those in the natural soil burial test. These results were supported by degraded surface of PBS and bio-composites observed through morphological study and the total colony count of natural soil was lower than that of compost soil. The biodegradability of the bio-composites was enhanced with increasing bio-flour content because the bio-flour is easily attacked by microorganisms. As the biodegradability test progressed over time up to 80 days, the molecular weight of PBS decreased in the soil burial test. We confirmed by attenuated total reflectance (FTIR-ATR) analyser that the chemical structures of PBS and the bio-composites were changed after the compost burial test. The glass transition temperature (T_g), melting temperature (T_m), crystallization temperature (T_c), heat of fusion (ΔH_f) and heat of crystallization (ΔH_c) of the natural and composted soil tested PBS were investigated using differential scanning calorimetry (DSC). From the results, we concluded that use of these bio-composites will reduce the environmental problems associated with waste pollution and the study findings support the predicted application of bio-composites as “green-composites” or “eco-materials”.     

Multiple melting behavior of poly(butylene succinate). II. Thermal analysis of isothermal crystallization and melting process

The multiple melting behavior of poly(butylene succinate) (PBSu) was studied with differential scanning calorimetry (DSC). Three different PBSu resins, with molecular weights (MWs) of 1.1 × 10⁵, 1.8 × 10⁵, and 2.5 × 10⁵, were isothermally crystallized at various crystallization temperatures (T_c) ranging from 70 to 97.5 °C. The T_c dependence of crystallization half‐time (τ) was obtained. DSC melting curves for the isothermally crystallized samples were obtained at a heating rate of 10 K min⁻¹. Three endothermic peaks, an annealing peak, a low‐temperature peak L, and a high‐temperature peak H, and an exothermic peak located between peaks L and H clearly appeared in the DSC curve. In addition, an endothermic small peak S appeared at a lower temperature of peak H. Peak L increased with increasing T_c, whereas peak H decreased. The T_c dependence of the peak melting temperatures [T_m(L) and T_m(H)], recrystallization temperature (T_re), and heat of fusion (ΔH) was obtained. Their fitting curves were obtained as functions of T_c. T_m(L), T_re, and ΔH increased almost linearly with T_c, whereas T_m(H) was almost constant. The maximum rate of recrystallization occurred immediately after the melting. The mechanism of the multiple melting behavior is explained by the melt‐recrystallization model. The high MW samples showed similar T_c dependence of τ, and τ for the lowest MW sample was longer than that for the others. Peak L increased with MW, whereas peak H decreased. In spite of the difference of MW, T_m(L), T_m(H), and T_re almost coincided with each other at the same T_c. The ΔH values, that is crystallinity, for the highest MW sample were smaller than those for the other samples at the same T_c. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2039–2047, 2005     

Crystallization behavior and thermal property of biodegradable poly(butylene succinate)/functional multi-walled carbon nanotubes nanocomposite

Biodegradable poly(butylene succinate) (PBSU)/functional multi-walled carbon nanotubes (f-MWNTs) nanocomposite were prepared by melt compounding. Nonisothermal crystallization and subsequent melting behavior, isothermal crystallization kinetics, spherulitic morphology, and crystal structure of neat PBSU and its nanocomposite were studied by differential scanning calorimetry, optical microscopy and wide angle X-ray diffraction in detail. The presence of f-MWNTs has a significant heterogeneous nucleation effect on the crystallization and morphology of PBSU, resulting in that the crystallization is enhanced during both nonisothermal and isothermal crystallization in the nanocomposite. Moreover, the crystal structure of PBSU is not modified by f-MWNTs in the nanocomposite. The thermogravimetric analysis illustrates an improvement in thermal stability of PBSU by around 10 °C in the presence of f-MWNTs compared with that of neat PBSU.     

Synthesis and characterization of biodegradable aliphatic copolyesters with poly(ethylene oxide) soft segments

A series of multiblock poly(ether-ester)s based on poly(butylene succinate) (PBS) as the hard segments and hydrophilic poly(ethylene oxide) (PEO) as the soft segments was synthesized with the aim of developing degradable polymers which could combine the mechanical properties of high performance elastomers with those of flexible plastics. The aliphatic poly(ether-ester)s were synthesized by the catalyzed two-step transesterification reaction of dimethyl succinate, 1,4-butanediol and α,ω-hydroxyl terminated poly(ethylene oxide) (PEO, = 1000 g/mol) in bulk. The content of soft PEO segments in the polymer chains was varied from about 10 to 50 mass%. The effect of the introduction of the soft PEO segments on the structure, thermal and physical properties, as well as on the biodegradation properties was investigated. The composition and structure of these aliphatic segmented copolyesters were determined by ¹H NMR spectroscopy. The molecular weights of the polyesters were verified by gel permeation chromatography (GPC), as well as by viscometry of dilute solutions and polymer melts. The thermal properties were investigated using differential scanning calorimetry (DSC). The degree of crystallinity was determined by means of DSC and wide-angle X-ray scattering. A depression of melting temperature and a reduction of crystallinity of the hard segments with increasing content of PEO segments were observed. Biodegradation of the synthesized copolyesters, estimated in enzymatic degradation tests in phosphate buffer solution with Candida rugosa lipase at 37 °C was compared with hydrolytic degradation in the buffer solution. The weight losses of the samples were in the range from 2 to 10 mass%. GPC analysis confirmed that there were significant changes in molecular weight of copolyesters with higher content of PEO segments, up to 40% of initial values. This leads to conclusion that degradation mechanism of the poly(ether-ester)s based on PEO segments occurs through bulk degradation in addition to surface erosion.     

The effect of self-nucleation on isothermal crystallization kinetics of poly(butylene succinate) (PBS) investigated by differential fast scanning calorimetry

Differential fast scanning calorimetry (DFSC) was employed on the study of self-nucleation behavior of poly(butylene succinate) (PBS).The ultra-fast cooling ability of DFSC allows investigating the effect of self-nucleation on the isothermal crystallization kinetics over a wide temperature range.Crystallization half-time,instead of crystallization peak temperature,was used to describe the self-nucleation behavior,and the self-nucleation domain for the samples crystallized at different temperatures was determined.Due to the competition between homogenous nucleation and self-nuclei,the effect of self-nucleation was less pronounced at high supercooling than that for the sample isothermally crystallized at higher temperature.An efficiency scale to judge the efficiency of nucleating agents from the crystallization half-time was also introduced in this work.     

Effect of poly(butylene succinate) crystals on spherulitic growth of poly(ethylene oxide) in binary blends of the two substances

The effects of the lamellar growth direction, extinction rings, and spherulitic boundaries of poly(butylene succinate) (PBSU) on the spherulitic growth of poly(ethylene oxide) (PEO) were investigated in miscible blends of the two crystalline polymers. In the crystallization process from a homogeneous melt, PBSU first developed volume‐filling spherulites, and then PEO spherulites nucleated and grew inside the PBSU spherulites. The lamellar growth direction of PEO was identical with that of PBSU even when the PBSU content was about 5 wt %. PEO, which intrinsically does not exhibit banded spherulites, showed apparent extinction rings inside the banded spherulites of PBSU. The growth rate of a PEO spherulite, G_PEO, was influenced not only by the blend composition and the crystallization temperature of PEO, but also by the growth direction with respect to PBSU lamellae, the boundaries of PBSU spherulites, and the crystallization temperature of PBSU, T_PBSU. The value of G_PEO first increased with decreasing T_PBSU when a PEO spherulite grew inside a single PBSU spherulite. Then, G_PEO decreased when T_PBSU was further decreased and a PEO spherulite grew through many tiny PBSU spherulites. This behavior was discussed based on the aforementioned factors affecting G_PEO. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 539–547, 2009     

Synthesis and characterization of biodegradable poly(butylene succinate-co-butylene fumarate)s

A series of aliphatic biodegradable polyesters modified with fumaric residues was synthesized by transesterification in the melt of dimethyl succinate, dimethyl fumarate and 1,4-butanediol. The amount of unsaturation, originating from the fumaric acid residues in the polyesters chains was varied from 5 to 20 mol%. The molecular structure and composition of the polyesters were determined by ¹H NMR spectroscopy. The effects of the content of fumaric residues on the thermal and thermo-oxidative properties of the synthesized polyesters were investigated using differential scanning calorimetry (DSC) and thermogravimetric analysis. The degree of crystallinity was determined by DSC and wide angle X-ray scattering. The degrees of crystallinity of the unsaturated copolyesters were reduced, while the melting temperatures were higher in comparison to poly(butylene succinate). Biodegradation of the synthesized copolyesters was estimated in enzymatic degradation tests using a buffer solution with Rhizopus arrhizus lipase at 37 °C. Although the degree of crystallinity of the copolyesters decreases slightly with increasing unsaturation, the biodegradation is not enhanced suggesting that not only the chemical structure and molecular stiffness but also the morphology of the spherulites has an influence on the biodegradation properties. The highest biodegradability was observed for the copolyesters containing 5 and 10 mol% of fumarate units.     

聚丁二酸丁二酯的无卤阻燃性能的研究

本文研究了聚苯基膦酸二苯砜酯(PSPPP)对聚丁二酸丁二酯(PBS)的阻燃作用。研究发现,在PBS中仅添加4wt%的PSPPP,其垂直燃烧就可以达到UL-94 V-0级,极限氧指数达到34,PSPPP对PBS表现出高效阻燃作用。然而,PSPPP对PBS有促进降解的作用,破坏了PBS的力学性能。通过在PBS/PSPPP体系中添加0.5wt%氧化锌后,有效抑制了PBS的降解,力学性能得到改善。