Crystallization, rheology and mechanical properties of the blends of poly(l-lactide) with supramolecular polymers based on poly(d-lactide)–poly(ε-caprolactone-co-δ-valerolactone)–poly(d-lactide) triblock copolymers

Synthesis of MPEG-b-PLLA Diblock Copolymers and Their Crystallization Performance with PDLA and PLLA Composite Films

Methoxy poly(ethylene glycol)-block-poly(L-lactide) (MPEG-b-PLLA) has a wide range of applications in pharmaceuticals and biology, and its structure and morphology have been thoroughly studied. In the experiment, we synthesized MPEG-b-PLLA with different block lengths using the principle of ring-opening polymerization by controlling the amount of lactic acid added. The thermodynamic properties of copolymers and the crystallization properties of blends were studied separately. The crystallization kinetics of PDLA/MPEG-b-PLA and PLLA/MPEG-b-PLA composite films were studied using differential scanning calorimetry (DSC). The results indicate that the crystallization kinetics of composite films are closely related to the amount of block addition. The crystallinity of the sample first increases and then decreases with an increase in MPEG-b-PLLA content. These results were also confirmed in polarized optical microscope (POM) and wide-angle X-ray diffraction (WAXD) tests. When 3% MPEG-b-PLLA was added to the PDLA matrix, the blend exhibited the strongest crystallization performance.

Morphology and Properties of Polylactic Acid Composites with Butenediol Vinyl Alcohol Copolymer Formed by Melt Blending

Due to its poor toughness and hydrophilicity, the application of polylactic acid (PLA) in the field of absorbent sanitary materials is restricted. A butenediol vinyl alcohol copolymer (BVOH) was used to improve PLA via melt blending. The morphology, molecular structure, crystallization, thermal stability, tensile property, and hydrophilicity of PLA/BVOH composites with different mass ratios were investigated. The results show that the PLA/BVOH composites possessed a two-phase structure with good interfacial adhesion. The BVOH could effectively blend into PLA without a chemical reaction. The addition of the BVOH promoted the crystallization of PLA, improved the perfection of the crystalline region, and increased the glass transition temperature and melting temperature of PLA in the heating process. Moreover, the thermal stability of PLA was markedly improved by adding the BVOH. The addition of the BVOH also had a significant effect on the tensile property of the PLA/BVOH composites. When the content of the BVOH was 5 wt.%, the elongation at the break of the PLA/BVOH composites could reach 9.06% (increased by 76.3%). In addition, the hydrophilicity of PLA was also significantly improved, and the water contact angles decreased with the increase in the BVOH content and time. When the content of the BVOH was 10 wt.%, the water contact angle could reach 37.3° at 60 s, suggesting good hydrophilicity.

Ductile poly(lactic acid)-based blends derived from poly(butylene succinate-co-butylene 2,5-thiophenedicarboxylate): Structures and properties

Because of superior tensile strength, biodegradability, and biocompatibility, poly(lactic acid) (PLA) has emerged as one among the growth-oriented biodegradable materials. But it has been limited to some extent in practical applications due to poor ductility. Consequently, in order to improve the drawback of poor ductility of PLA, ductile blends were obtained by melt-blending of poly(butylene succinate-co-butylene 2,5-thiophenedicarboxylate) (PBSTF25) with PLA. PBSTF25 has a good improvement on the ductility of PLA due to its excellent toughness. Differential scanning calorimetry (DSC) showed that PBSTF25 promoted the cold crystallization of PLA. Wide-angle X-ray diffraction (XRD) results revealed that PBSTF25 experienced stretch-induced crystallization throughout the stretching procedure. Scanning electron microscopy (SEM) showed neat PLA had a smooth fracture surface, but the blends had rough fracture surface. PBSTF25 can improve the ductility and processing properties of PLA. When the addition of PBSTF25 reached 20 wt%, tensile strength was 42.5 MPa and elongation at break increased to 156.6 %, approximately 19 times as much as PLA. The toughening effect of PBSTF25 was better than that of poly(butylene succinate).

Designing Strong, Tough, Fluorescent, and UV-Shielding PLA Materials by Incorporating a Phenolic Compound-Based Multifunctional Modifier

The realization of high stiffness, high extensibility, and multi-functions for polylactic acid (PLA) is a vital issue for its practical applications. Herein, hydroxyalkylated tannin acid (mTA), a phenolic compound-based modifier with plentiful flat aromatic structures and flexible isopropanol oligomers, is designed and fabricated to act as the multifunctional modifier for PLA. The mTA exhibits the capability of emitting fluorescence and blocking UV light due to the combination of flat aromatic structures and plentiful flexible chains. Besides, mTA with high grafting degree (h-mTA) shows an excellent compatibility to PLA due to the hydrogen bonding interface and the high affinity of grafted isopropanol oligomers to PLA. As a result, the as-prepared PLA/h-mTA20 composite exhibits a strikingly improved extensibility by 61.2 times while maintaining the high yield strength of PLA. Moreover, PLA/h-mTA can serve as a fluorescent material with multi-mode responsiveness as well as a UV-shielding material with high transparency. We envision that this work opens a novel yet facile way to prepare a strong, tough, and multifunctional PLA material with expanded application scopes and will promote the practical applications of phenolic compounds in polymers.

Toughening Modification of Polylactic Acid by Thermoplastic Silicone Polyurethane Elastomer

The melt blending of polylactic acid (PLA) and thermoplastic silicone polyurethane (TPSiU) elastomer was performed to toughen PLA. The molecular structure, crystallization, thermal properties, compatibility, mechanical properties and rheological properties of the PLA/TPSiU blends of different mass ratios (100/0, 95/5, 90/10, 85/15 and 80/20) were investigated. The results showed that TPSiU was effectively blended into PLA, but no chemical reaction occurred. The addition of TPSiU had no obvious effect on the glass transition temperature and melting temperature of PLA, but slightly reduced the crystallinity of PLA. The morphology and dynamic mechanical analysis results demonstrated the poor thermodynamic compatibility between PLA and TPSiU. Rheological behavior studies showed that PLA/TPSiU melt was typically pseudoplastic fluid. As the content of TPSiU increased, the apparent viscosity of PLA/TPSiU blends showed a trend of rising first and then falling. The addition of TPSiU had a significant effect on the mechanical properties of PLA/TPSiU blends. When the content of TPSiU was 15 wt%, the elongation at break of the PLA/TPSiU blend reached 22.3% (5.0 times that of pure PLA), and the impact strength reached 19.3 kJ/m2 (4.9 times that of pure PLA), suggesting the favorable toughening effect.

Biodegradable shape-memory polymers and composites

Polymers have recently been making media headlines in various negative ways. To combat the negative view of those with no polymer experience, sustainable and biodegradable materials are constantly being researched. Shape-memory polymers, also known as SMPs, are a type of polymer material that is being extensively researched in the polymer industry. These SMPs can exhibit a change in shape because of an external stimulus. SMPs that are biodegradable or biocompatible are used extensively in medical applications. The use of biodegradable SMPs in the medical field has also led to research of the material in other applications. The following categories used to describe SMPs are discussed: net points, composition, stimulus, and shape-memory function. The addition of fillers or additives to the polymer matrix makes the SMP a polymer composite. Currently, biodegradable fillers are at the forefront of research because of the demand for sustainability. Common biodegradable fillers or fibers used in polymer composites are discussed in this chapter including Cordenka, hemp, and flax. Some other nonbiodegradable fillers commonly used in polymer composites are evaluated including clay, carbon nanotubes, bioactive glass, and Kevlar. The polymer and filler phase differences will be evaluated in this chapter. The recent advances in biodegradable shape-memory polymers and composites will provide a more positive perspective of the polymer industry and help to attain a more sustainable future.

Toughening Polylactic Acid by a Biobased Poly(Butylene 2,5-Furandicarboxylate)-b-Poly(Ethylene Glycol) Copolymer: Balanced Mechanical Properties and Potential Biodegradability

Polylactic acid (PLA) is a biodegradable thermoplastic polyester produced from natural resources. Because of its brittleness, many tougheners have been developed. However, traditional toughening methods cause either the loss of modulus and strength or the lack of degradability. In this work, we synthesized a biobased and potentially biodegradable poly(butylene 2,5-furandicarboxylate)-b-poly(ethylene glycol) (PBFEG50) copolymer to toughen PLA, with the purpose of both keeping mechanical strength and enhancing the toughness. The blend containing 5 wt % PBFEG50 exhibited about 28.5 times increase in elongation at break (5.5% vs 156.5%). At the same time, the tensile modulus even strikingly increased by 21.6% while the tensile strength was seldom deteriorated. Such a phenomenon could be explained by the stretch-induced crystallization of the BF segment and the interconnected morphology of PBFEG50 domains in PLA5. The Raman spectrum was used to identify the phase dispersion of PLA and PBFEG50 phases. As the PBFEG50 content increased, the interconnected PBFEG50 domains start to separate, but their size increases. Interestingly, tensile-induced cavitation could be clearly identified in scanning electron microscopy images, which meant that the miscibility between PLA and PBFEG50 was limited. The crystallization of PLA/PBFEG50 blends was examined by differential scanning calorimetry, and the plasticizer effect of the EG segment on the PLA matrix could be confirmed. The rheological experiment revealed decreased viscosity of PLA/PBFEG50 blends, implying the possible greener processing. Finally, potential biodegradability of these blends was proved.