Selective localization of starch nanocrystals in the biodegradable nanocomposites probed by crystallization temperatures

Effect of hydrophobic modification of chitin nanocrystals on role as anti-nucleator in the crystallization of poly(ε-caprolactone)/polylactide blend

Biodegradable polymer blends filled with rod-like polysaccharide nanocrystals have attracted much attention because each component in this type of ternary composites is biodegradable, and the final properties are more easily tailored comparing to those of binary composites. In this work, chitin nanocrystals (ChNCs) were used as nanofiller for the biodegradable poly(ε-caprolactone) (PCL)/polylactide (PLA) immiscible blend to prepare ternary composites for a crystallization study. The results revealed that the crystallization behavior of PCL/PLA blend matrices strongly depended on the surface properties of ChNCs. Non-modified ChNCs and modified ChNCs played completely different roles during crystallization of the ternary systems: the former was inert filler, while the latter acted as anti-nucleator to the PCL phase. This alteration was resulted from the improved ChNC-PCL affinity after modification of ChNCs, which was due to the 'interfacial dilution effect' and the preferential dispersion of ChNCs. This work presents a unique perspective on the nucleation role of ChNCs in the crystallization of immiscible PCL/PLA blends, and opens up a new application scenario for ChNCs as anti-nucleator.

Poly(3-hydroxybutyrate) nanocomposites modified with even and odd chain length polyhydroxyalkanoates

Poly(3-hydroxybutyrate) (PHB) was blended with medium-chain-length PHAs (mcl-PHAs) for improving its flexibility while nanocellulose (NC) was added as a reinforcing agent. Even and odd-chain-length PHAs, having as main component poly(3-hydroxyoctanoate) (PHO) or poly(3-hydroxynonanoate) (PHN) were synthesized and served as PHB modifiers. The effects of PHO and PHN on the morphology, thermal, mechanical and biodegradation behaviors of PHB were different, especially in the presence of NC. The addition of mcl-PHAs decreased the storage modulus (E') of PHB blends by about 40 %. The further addition of NC mitigated this decrease bringing the E' of PHB/PHO/NC close to that of PHB and having a minor effect on the E' of PHB/PHN/NC. The biodegradability of PHB/PHN/NC was higher than that of PHB/PHO/NC, the latter's being close to that of neat PHB after soil burial for four months. The results showed a complex effect of NC, which enhanced the interaction between PHB and mcl-PHAs and decreased the size of PHO/PHN inclusions (1.9 ± 0.8/2.6 ± 0.9 μm) while increasing the accessibility of water and microorganisms during soil burial. The blown film extrusion test showed the ability of mcl-PHA and NC modified PHB to stretch forming uniform tube and supports the application of these biomaterials in the packaging sector.

Effect of shear and heat milling of starch on the properties of tapioca starch/cellulose nanofiber composites

Thermoplastic starch was prepared from tapioca starch (TS) and thermo-mechanical modified TS (ModifiedTS) using glycerol as a plasticizer and cellulose nanofiber (CNF) as a reinforcement. The ModifiedTS was produced using shear-and-heat milling machining (SHMM), which effectively reduced starch crystallinity and transformed the granule shape without a chemical reaction. The modified starch with low crystallinity and numerous active hydrogen bonds clearly showed Vh crystal structure after blending with glycerol. The mechanical properties changed significantly upon addition of 10 wt% CNF into plasticized ModifiedTS, which enhanced the yield strength and decreased the elongation at break. A dynamic mechanical analysis revealed a higher glass transition temperature (Tg) of the ModifiedTS films. Tg for the starch film increased from 9.3 °C of the TS film to 29.8 °C of the ModifiedTS film. These results suggest that SHMM provides the ability to widely adjust the mechanical properties of glycerol plasticized starch materials by enhancing interfacial interactions with CNF.

Novel Production Methods of Polyhydroxyalkanoates and Their Innovative Uses in Biomedicine and Industry

Polyhydroxyalkanoate (PHA), a biodegradable polymer obtained from microorganisms and plants, have been widely used in biomedical applications and devices, such as sutures, cardiac valves, bone scaffold, and drug delivery of compounds with pharmaceutical interests, as well as in food packaging. This review focuses on the use of polyhydroxyalkanoates beyond the most common uses, aiming to inform about the potential uses of the biopolymer as a biosensor, cosmetics, drug delivery, flame retardancy, and electrospinning, among other interesting uses. The novel applications are based on the production and composition of the polymer, which can be modified by genetic engineering, a semi-synthetic approach, by changing feeding carbon sources and/or supplement addition, among others. The future of PHA is promising, and despite its production costs being higher than petroleum-based plastics, tools given by synthetic biology, bioinformatics, and machine learning, among others, have allowed for great production yields, monomer and polymer functionalization, stability, and versatility, a key feature to increase the uses of this interesting family of polymers.

Polyhydroxybutyrate blends: A solution for biodegradable packaging?

Poly (3-hydroxybutyrate) (PHB) is a valuable bio-based and biodegradable polymer that may substitute common polymers in packaging and biomedical applications provided that the production cost is reduced and some properties improved. Blending PHB with other biodegradable polymers is the most simple and accessible route to reduce costs and to improve properties. This review provides a comprehensive overview on the preparation, properties and application of the PHB blends with other biodegradable polyesters such as medium-chain-length polyhydroxyalkanoates, poly(ε-caprolactone), poly(lactic acid), poly(butylene succinate), poly(propylene carbonate) and poly (butylene adipate-co-terephthalate) or polysaccharides and their derivatives. A special attention has been paid to the miscibility of PHB with these polymers and the compatibilizing methods used to improve the dispersion and interface. The changes in the PHB morphology, thermal, mechanical and barrier properties induced by the second polymer have been critically analyzed in view of industrial application. The biodegradability and recyclability strategies of the PHB blends were summarized along with the processing techniques adapted to the intended application. This review provides the tools for a better understanding of the relation between the micro/nanostructure of PHB blends and their properties for the further development of PHB blends as solutions for biodegradable packaging.

Progresses in synthetic technology development for the production of L-lactide

L-Lactide is an intermediate for the industrial production of polylactic acid (PLA). The chemical and optical purities of lactide determine the quality of the prepared PLA. It is of great challenge to synthesize L-lactide efficiently with high chemical and optical purities under the conditions applicable for industrial production. With the national plastic reduction order issued, developing biodegradable materials such as PLA has gradually become a hot topic, and the production of upstream lactide is the key technique for the whole industrial chain. This mini-review aims to summarize typical works on the related synthetic technology development in recent years.

Reactive extrusion-processed native and phosphated starch-based food packaging films governed by the hierarchical structure

The aim of this research work was to investigate novel tools given by nanotechnology and green chemistry for improving the disadvantages typically associated to the starch-based films: water susceptibility and brittle mechanical behavior. With this in mind, four food packaging film systems were developed from corn starch or corn starch nanocrystals (SNCs), and modified by phosphating under reactive extrusion (REx) conditions using sodium tripolyphosphate (Na₅P₃O₁₀ - TPP) as a crosslinker. The structural, physicochemical, thermal, rheological and mechanical properties, as well as studies associated with the management of carbohydrate polymer-based plastic wastes (biodegradability and compostability) were carried out in this study. The hierarchical structure and the modification of the starch were dependent on the amylose content and degree of substitution (DS), which in turn depended on the hydrogen (H)-bonding interactions. In both cases, a higher molecular ordering of the starch chains in parallel was decisive to obtain the self-assembled thermoplastic starches. Beyond the valuable results obtained and scientifically analyzed, unfortunately none of the manufactured materials achieved to improve their performance compared to the control film (thermoplastic starch - TPS). It was even thought that the phosphated starch-based films could fertilize lettuce (Lactuca sativa) seedlings during their biodegradation, and this was not achieved either. This possibly due to the low content of phosphorus or its poor bioavailability.

Surface chain engineering of chitin nanocrystals towards tailoring the nucleating capacities for poly(β-hydroxybutyrate)

Chitin nanocrystal (ChNC) is good nucleation agent for aliphatic polyesters because of its high-energy surface. To moderate its nucleation activity, silane coupling agents with different chain lengths or functional groups were used to modify ChNCs in this work, and biodegradable poly(β-hydroxybutyrate) (PHB) was used as target polymer for crystallization study. Surface coupling of ChNCs improves their phase adhesion to PHB chain and weakens their nucleation activities. The alterations strongly depend on the surface chain structure of ChNCs: sulfhydryl silane-coupled ChNC shows lowered nucleation activity, whereas amino silane-coupled ChNCs even become antinucleation agents. The interfacial compatibility is vital to altered role of ChNCs and to following changes in spherulite growth and ring-banded morphology, which is further disclosed using Flory-Huggins interaction parameters and rheological responses as probes. This work provides useful information on tailoring the functions of ChNCs as nanoadditive for biodegradable aliphatic polyesters by the way of surface chain engineering.

Starch nanocrystals as the particle emulsifier to stabilize caprylic/capric triglycerides-in-water emulsions

Starch nanocrystals (SNCs) grafted with octenyl succinic anhydride (OSA) were used to stabilize caprylic/capric triglycerides (GTCC)-in-water emulsions. The morphology and viscoelasticity of emulsions were studied in terms of particle loadings and degrees of substitution (DSs). It is found that the emulsifying capacities of SNCs increase with increased DSs. Both the pristine SNC and modified ones can be well used to stabilize emulsions, whereas the emulsification follows different mechanisms. The platelet-like structure of SNCs, together with its improved amphiphilicity after surface treatments, are important to the formation and evolution of droplet clusters. The deformation and relaxation of those clusters result in weak flow overshoots and strong thixotropy in different shear flow fields, which favor storage and applications of GTCC-in-water emulsions as hydrocolloids. The mechanisms were then discussed in terms of rigidity of SNC and relaxations of clusters. This work proposes a promising application of SNC in food and cosmetic industries.

Skin-Compatible Biobased Beauty Masks Prepared by Extrusion

In the cosmetic sector, natural and sustainable products with a high compatibility with skin, thus conjugating wellness with a green-oriented consumerism, are required by the market. Poly(hydroxyalkanoate) (PHA)/starch blends represent a promising alternative to prepare flexible films as support for innovative beauty masks, wearable after wetting and releasing starch and other selected molecules. Nevertheless, preparing these films by extrusion is difficult due to the high viscosity of the polymer melt at the temperature suitable for processing starch. The preparation of blends including poly(butylene succinate-co-adipate) (PBSA) or poly(butylene adipate-co-terephthalate) (PBAT) was investigated as a strategy to better modulate melt viscosity in view of a possible industrial production of beauty mask films. The release properties of films in water, connected to their morphology, was also investigated by extraction trials, infrared spectroscopy and stereo and electron microscopy. Then, the biocompatibility with cells was assessed by considering both mesenchymal stromal cells and keratinocytes. All the results were discussed considering the morphology of the films. This study evidenced the possibility of modulating thanks to the selection of composition and the materials processing of the properties necessary for producing films with tailored properties and processability for beauty masks.

Impact of the Surface Properties of Cellulose Nanocrystals on the Crystallization Kinetics of Poly(Butylene Succinate)

The hydrophilicity of cellulose nanocrystals (CNCs) is a major challenge for their processing with hydrophobic polymers and matrices. As a result, many surface modifications have been proposed to hydrophobize CNCs. The authors showed in an earlier study that grafting alcohols of different chain lengths onto the surface of CNCs using toluene diisocyanate (TDI) as a linker can systematically hydrophobize CNCs to a water contact angle of up to 120° depending on the alcohol chain length. Then, the hydrophobized CNCs were used to mechanically reinforce poly(butylene succinate) (PBS), which is a hydrophobic polymer. As a result of hydrophobization, PBS/CNCs interfacial adhesion and the composite mechanical properties significantly improved with the increasing CNC contact angle. Continuing on these results, this paper investigates the impact of CNC surface properties on the crystallization behavior of PBS using differential scanning calorimetry (DSC). The results showed that the crystallization temperature of PBS increased from 74.7 °C to up to 86.6 °C as a result of CNC nucleation activity, and its value was proportionally dependent on the contact angle of the CNCs. In agreement, the nucleation activity factor (φ) estimated using Dobreva and Gutzow’s method decreased with the increasing CNC contact angle. Despite the nucleation action of CNCs, the rate constant of PBS crystallization as estimated using the Avrami model decreased in general as a result of a prevailing impeding effect. This decrease was minimized with increasing the contact angle of the CNCs. The impeding effect also increased the average activation energy of crystallization, which was estimated using the Kissinger method. Moreover, the Avrami exponent (n) decreased because of CNC addition, implying a heterogeneous crystallization, which was also apparent in the crystallization thermograms. Overall, the CNC addition facilitated PBS nucleation but retarded its crystallization, and both processes were significantly affected by the surface properties of the CNCs.

Cellulose nanofibers reinforced biodegradable polyester blends: Ternary biocomposites with balanced mechanical properties

Blending two biodegradable aliphatic polyesters with complementary bulk properties is an easy way of tuning their final properties. In this work, the ductile poly(butylene succinate) was mixed with polylactide, and as expectable, the blends show improved toughness with sharply reduced strengths. The pristine cellulose nanofibers were then used as the reinforcement for the blends. It is found that most nanofibers are dispersed in the polylactide phase because polylactide has better affinity to nanofibers, and the lower viscosity level of polylactide also favors driving nanofibers into the continuous polylactide phase during melting mixing. In this case, the strength and rigidity losses resulted from the presence of soft poly(butylene succinate) phase are compensated to some extent. To further improve mechanical properties, a two-step approach (reactive processing of blends, followed by the incorporation with nanofibers) was developed. This work provides an interesting way of fabricating fully biodegradable composites with well-balanced mechanical performance.