Biodegradation of poly(lactic acid)—cassava bagasse composites produced by injection molding

Neat poly (lactic acid) (PLA) and PLA/cassava bagasse (CB) composites were used to produce seedling tubes by extrusion and injection molding. The tubes were buried in simulated soil, and their biodegradation was investigated by weight loss, scanning electron microscopy (SEM), and Fourier transform infrared spectroscopy (FTIR). After 180 days, the composites' biodegradation was higher than neat PLA material, and the higher the CB content, the higher the biodegradation, which caused fissures and voids in the material. The biodegradation of PLA/CB composites increased the phosphorus content in the soil after 180 days. Composites of PLA with CB, an abundant agro-industrial residue in Brazil, are promising because they can reduce the environmental impact due to CB's proper destination, and the composites' costs and biodegradation are faster than pure PLA material. Both the faster biodegradation of the tube and the higher P content are advantageous for seedling tubes.     

Novel biodegradable low-density polyethylene–poly(lactic acid)–starch ternary blends

The ternary powder blends based on low-density polyethylene (LDPE) and two polymers of natural origin poly(lactic acid) (PLA) and starch are obtained in a rotor disperser under conditions of shear deformations. The dependence of the final powder dispersity on the composition is explored. A comparative analysis of the mechanical properties of the ternary blends with those of the LDPE–PLA and PLA–starch binary blends previously obtained has revealed that the presence of two rigid polymers PLA and starch leads to an increase in the elastic modulus and a decrease in the tensile strength and elongation at break. In the study of the blend biodegradability, it is found that the presence of two polymers of natural origin in the system with a total mass fraction of 60% promotes intensive biodegradation.     

Poly(lactic acid)–thermoplastic starch–cotton composites: Starch-compatibilizing effects and composite biodegradability

Poly(lactic acid) (PLA) is a biodegradable, brittle, and high-cost polymer, which can be applied over structural components and green packaging. In this study, we reinforced PLA with natural cotton (10 wt %) and thermoplastic starch (TPS; 3 wt %) to obtain a biodegradable and lower cost composite. TPS was incorporated in three distinct ways: it was blended, coated, and blended and coated. In this study, we investigated the compatibilization of TPS in the improvement of matrix-reinforcement adhesion and increase in the tensile behavior without a compromise in biodegradation. The samples were investigated with thermal analysis, dynamic mechanical thermal analysis, tensile testing, scanning electron microscopy, confocal laser scanning microscopy, and hydrolytic degradation. The results show that the coupling effect was more pronounced in the PLA_TPS–cotton_TPS (hybrid system with PLA and cotton) hybrid system. This formulation presented a higher glass-transition temperature, thermal stability, storage modulus, wettability, and ductility. The TPS addition improved the adhesion between the matrix and starched cotton fiber and retarded abiotic biodegradation. These properties will allow for green applications. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47490.     

Cellulose nanofibre–poly(lactic acid) microcellular foams exhibiting high tensile toughness

We report here the morphology and tensile properties of polylactic acid–cellulose nanofibre (PLA–CNF) microcellular nanocomposites. Two types of CNF were used for the nanocomposite preparation, native and surface acetylated CNF (ac-CNF). Samples were foamed in a mould to enable tensile testing. The effect of the mould use on the foam morphology was first assessed by comparison with free foamed samples. We found that the mould affected the cell growth stage of the foaming process in neat PLA foam while its effect was less important in nanocomposites. Stiffening and strengthening effect of CNF was greatly enhanced by foaming when compared to their solid counterparts. The most notable change in tensile properties was however the large increase in strain at break resulting in the high tensile toughness of microcellular PLA–CNF nanocomposites. Strain at break increased up to 7.5 times in neat PLA and up to 31.5 times in the foam containing 3% of CNF. Surface acetylation of CNF significantly affected the properties of foams with 9% of CNF loading: while foams with ac-CNF were stiffer, foams with native CNF exhibited higher strain at break and so higher overall toughness.     

Nanosized micelles self-assembled from amphiphilic poly(citric acid)–poly(ε-caprolactone)–poly(citric acid) copolymers

In this study, novel ABA-type amphiphilic copolymers consisting of poly(citric acid) (PCA) (A) as hydrophilic segment and poly(ε-caprolactone) (PCL) (B) as hydrophobic block were prepared by an approach in the following two steps: (1) ring-opening polymerization (ROP) of ε-caprolactone with 1,5-pentanediol initiator to obtain a hydroxyl telechelic PCL; (2) melt polycondensation reaction of hydroxyl telechelic PCL and citric acid molecules. The prepared copolymers are capable of self-assembling into nanosized micelles in aqueous solution. The influence of the copolymer composition on the micelle dimensions was investigated. The critical micellar concentration of the copolymers is in the range of 5–6.3 × 10^?2 mg/mL which is determined by the fluorescence probe technique using pyrene. Also the results indicate that CMC of self assembled micelles is influenced by the hydrophilicity of PCA–PCL–PCA copolymers depending on the CA/CP ratio, and these micelles may find great potential as drug carriers in biomedical fields.     

Double yielding behavior of in situ microfibrillar polyolefin elastomer/poly(lactic acid) composites: Effect of microfibrillar morphology

In situ microfibrillar composites (MFCs), with polyolefin elastomer as matrix and poly(lactic acid) (PLA) as dispersed phase, were successfully prepared using multistage stretching extrusion system. Interestingly, a peculiar phenomenon of double yielding was observed on the stress-strain curves of MFCs under tensile loading for the first time. The MFCs with 20 wt% PLA microfibrils exhibited two distinct yield points, and a pronounced hump appeared on the stress-strain curve of PLA-20. Two-dimensional small-angle X-ray scattering analyses showed that the equatorial streak scattering became stronger with increase in PLA microfibrillar content; the meridional scattering trace became stronger with increase in tensile strain for PLA-20. The rheological analysis showed that the G′ of PLA-20 had a plateau in the low frequency region and did not depend on frequency changes.     

Surface texture and barrier performance of poly(lactic acid)–cellulose nanocrystal extruded-cast films

In this study, we assessed the influence of cellulose nanocrystal (CNC) addition level (0.5–2 wt %) on the surface texture, thickness, and barrier properties of poly(lactic acid) (PLA) extruded-cast films. Regardless of the CNC content, the addition of CNC increased the surface average roughness and maximum roughness of the PLA films in both the machine and cross-machine directions because of the presence of CNC agglomerates. The increased roughness resulted in films with uneven thicknesses; this affected their accurate measurements with a conventional micrometer. Rather, accurate thickness measurements were obtained through the density method, a more appropriate thickness measurement method for films with rough surfaces. The permeability values were negatively correlated with the increased crystallinity. Both the water vapor permeability and oxygen permeability (OP) values decreased significantly by approximately 26–45 and 25–50%, respectively, as the CNC content increased from 0.5 to 2 wt % because of the tortuosity effect. The OP values of the neat PLA and composite films remained insensitive to changes in the relative humidity (from 0 to 75%) when they were tested at 23 °C. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47594.     

Structure–property relationship for poly(lactic acid) (PLA) filaments: physical,thermomechanical and shape memory characterization

Physical, thermomechanical, and shape memory properties of two different samples of poly(lactic acid) (PLA) multifilament yarns were determined using various complementary techniques. The birefringence and crystalline fraction of one sample was higher than the other filaments sample indicating higher molecular orientation and compactness. For both filaments, two distinct morphological features with different sizes in the order of few nanometers (less than 50 nm) were found using AFM and SAXS techniques. The glass transition temperature (T_g) of the samples were ranged from 61 °C to 76 °C depends on the sample and the methods of measurement. Partial storage modulus (E′) increase above T_gas well as additional small peak in loss modulus (E″) of the lower crystallinity sample was assigned to recrystallization. The multiple overlapped peaks in the E″ and tan δ curves and subsequent crystallization along with exothermic peak right after T_g suggests the existence of both relaxed and oriented amorphous regions. The rigid crystalline regions prevented the shrinkage and enhanced dimensional stability. Multifilament yarn with higher crystallinity and total molecular orientation showed higher modulus (both dynamic and static) and strength and lower elongation at break. The oriented non-crystalline regions in the multifilament yarn sample led to moderate modulus and strength along with high elongation at break. The shape recovery of both samples with different structural parameters stayed almost constant (~50 %) upon the deformation temperature rise.     

Morphological characteristics and thermal,rheological, and mechanical properties of cellulose nanocrystals-containing biodegradable poly(lactic acid)/poly(ε-caprolactone) blend composites

This work investigates the effect of cellulose nanocrystal (CN) loading on the properties of polylactide / poly(ε-caprolactone) (PLA/PCL) (70/30) blend processed in a twin-screw extruder as a potential material that can be utilized in various applications where biodegradation is highly desired. The morphological analysis revealed a reduction in droplet size of dispersed PCL phase upon addition of CN at low concentrations (1 and 2 wt %) with maximum reduction at 2 wt % which led to maximum improvement in mechanical properties. The reinforcing effect of CN in increasing the DMA storage modulus of the prepared systems was noticed when CN concentration was increased. Further, CN enhanced the crystallization of PCL, whereas the cold crystallization of PLA remained the same with CN addition. Both melt strength and viscosity of PLA improved with the incorporation of PCL and CN. In general, a green composite material with improved properties was successfully prepared using an environmentally friendly filler material. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 137, 48665.     

Tetracycline hydrochloride-containing poly (ε-caprolactone)/poly lactic acid scaffold for bone tissue engineering application: in vitro and in vivo study

In the current study, tetracycline hydrochloride (TCH), an antibiotic against most of the medically relevant bacteria, was incorporated into poly (ε-caprolactone)/poly lactic acid solution in order to develop a composite scaffold with both antibacterial and osteoinductive properties for the repair of infected bone defects. The composite scaffolds were produced from poly (ε-caprolactone) (PCL) and poly lactic acid (PLA) solution (1:1 (w/w)) incorporated with 3, 5, and 10% (w/w) of TCH by thermally induced phase separation technique. The scaffolds were evaluated regarding their morphology, wettability, porosity, degradation, mechanical properties, and cellular response. The scaffold containing 10% of TCH (PCL/PLA/TCH10%) was chosen as the optimum scaffold for further investigation in a rat femoral defect model. The study showed that after eight weeks, the bone formation was relatively higher in PCL/PLA/TCH10%-treated group with completely filled defect when compared with control (PCL/PLA scaffold without TCH). Histopathological evaluation showed that the defect in PCL/PLA/TCH10%-treated group was fully replaced by new bone and connective tissue. Our results provide evidence supporting the possible applicability of TCH-containing scaffolds for successful bone regeneration.     

Disclosing the role of surface and bulk erosion on the viscoelastic behavior of biodegradable poly(ε-caprolactone)/poly(lactic acid)/hydroxyapatite nanocomposites

In this study, biodegradable polymer blends and their nanocomposites were prepared using poly(ε-caprolactone) (PCL) and poly(lactic acid) (PLA) as blending components and hydroxyapatite (HA) nanoparticles as reinforcement. X-ray diffraction spectra showed that the presence of HA nanoparticles enhanced the intensity of the peaks (100) and (200) corresponding to the PCL's crystalline planes. The transmission electron microscopy images confirmed the high tendency of HA nanoparticles to locate in the PLA phase. The water uptake values of samples measured at pH 4 were more than those measured at other pH values. The weight loss behavior of blends in acidic medium was completely different from that in basic and neutral media. The Williams–Landel–Ferry equation and time–temperature superposition principle were applied to the creep compliance of the samples and their master curves were determined at reference temperature of 30 °C, and the mechanical properties of samples were predicted in other conditions. The effect of pH on the creep–recovery response of studied samples was analyzed. From this analysis, it could be found that at pH 4, the creep stain increased, while, at pH 7, there was no a significant change in the viscoelastic property. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47151.     

Synthesis of poly(lactic acid)–poly(ethylene glycol) copolymers using multi-SO3H-functionalized ionic liquid as the efficient and reusable catalyst

Poly(lactic acid)–poly(ethylene glycol) copolymers were synthesized under the catalysis of multi-SO₃H-functionalized ionic liquid. Compared to the ordinary ionic liquids and the traditional Lewis acid catalysts, the ionic liquids with multi-sulfonic acid groups were more catalytically active, and the reaction conversion rate reached up to 97.8 %. The molecular weight of the resulting copolymer was 5.69 × 10⁴ g mol^?1 and the degree of crystallinity was 42.9 %. The copolymers were also of higher hydrophilicity and better mechanical properties. The reaction kinetics of copolymerization was analyzed. The intrinsically high catalytic activity of multi-SO₃H groups originated from the lower activation energy and the higher free acidity. The recovering catalytic activity of the multi-SO₃H ionic liquid catalyst was higher, suggesting that it is a recyclable, environmentally friendly catalyst.     

Hot pressed hydroxyapatite–carbon fibre composites

Composite samples were obtained from hydroxyapatite powder and carbon fibres by hot pressing at 1100°C and 25 MPa for 15 min in argon atmosphere. Two types of cut carbon fibres produced in a carbonisation process of polyacrylonitrile (PAN) precursor were used both in non-coated or coated form. The coatings of calcium phosphate were applied by sol–gel technique. The highly sintered composite with the best strength properties was obtained from coated carbon fibres with basic character of the surface. The existence of hydroxyl groups on fibre surface makes possible formation of bonds with the calcium phosphate layer formed as a result of polycondensation following the sol–gel procedure.     

Single-component poly(ε-caprolactone) composites

Non-covalently bonded crystalline inclusion compounds (ICs) have been formed by threading host cyclic starches, α-cyclodextrins (α-CDs), onto guest poly(ε-caprolactone) (PCL) chains and by co-crystallization of guest PCL and host urea (U). PCLs were coalesced from both ICs by appropriate removal of the α-CD and U hosts. When added at low concentrations, PCL coalesced from its α-CD–IC served as an effective self-nucleating agent for the bulk crystallization of as-received PCL from the melt. Film sandwiches consisting of two layers of as-received (asr) (control), and one layer each of asr and self-nucleated (nuc) (composite) PCLs were produced by melt pressing. A composite sandwich consisting of a film of neat PCL coalesced from its U–IC (c-PCL) and a film of asr-PCL was also melt pressed. DSC showed that both composite films maintain their characteristic structures and properties even after melt-pressing them together. Both single component film sandwiches exhibited strong interfaces and better mechanical properties than the asr-PCL/asr-PCL control composite sandwiches. These results are similar to those previously obtained on similarly prepared nylon-6 (N-6) sandwich composites made with asr- and nuc-N-6 films with the same levels of crystallinity. However, while the elongation at break was greatly reduced in the asr-N-6/nuc-N-6 composite, asr-/asr-, asr-/c-, and asr-/nuc-, PCL/PCL-composites all showed similarly large elongations at break. The above room temperature and well below room temperature glass-transition temperatures of N-6 and PCL are likely the cause of their widely different elongations at break.     

Comparison of poly(ethylene-co-acrylic acid) loaded Zn2+–montmorillonite nanocomposites and poly(ethylene-co-acrylic acid) zinc salt

Novel nanocomposite films based on poly(ethylene-co-acrylic acid) (PEAA) and zinc montmorillonite (Zn²⁺–MMT) were fabricated using a solution casting method with water as the solvent. Transmission electron microscopy indicated that Zn²⁺–MMT was distributed finely in the PEAA matrix. X-ray diffraction indicated that an ion exchange process occurs between Zn²⁺–MMT and PEAA. The nanocomposites filled with a low Zn²⁺–MMT loading increased the tensile strength and elongation at break. The significant improvements in these mechanical properties were attributed to the fine dispersion of Zn²⁺–MMT in the polymer and the covalent interaction between the polymer chains and Zn²⁺ cations. Thermogravimetric analysis and differential thermal calorimetry confirmed that PEAA formed a network through the presence of Zn²⁺ cations. A poly(ethylene-co-acrylic acid) zinc salt (PEAAZn) film by hot pressing was introduced for comparison. Zn²⁺–MMT improved the mechanical properties of the PEAA significantly compared to that of PEAAZn.     

New hydroxyapatite–hydrotalcite composites I. synthesis

The synthesis and characterization of original materials, composed by hydrotalcite and hydroxyapatite, is discussed. All the syntheses were carried out in presence of microwave irradiation during the crystallization step. The interactions between the two compounds depend on the synthesis procedure. If hydroxyapatite is incorporated to hydrotalcite, the first compound is encapsulated by hydrotalcite. Instead, if hydroxyapatite is first prepared, the resulting solid is essentially a hydrotalcite with interlayered hydroxyapatite. When the composite material is synthesized by a simultaneous coprecipitation, the small clusters of hydroxyapatite and hydrotalcite are homogeneously dispersed. Consequently, the specific surface area and the particle size vary.     

Effect of poly(ε-caprolactone) and titanium (IV) dioxide content on the UV and hydrolytic degradation of poly(lactic acid)/poly(ε-caprolactone) blends

The effect of accelerated weathering degradation on the properties of poly(lactic acid) (PLA)/poly(ε-caprolactone) (PCL) blends and PLA/PCL/titanium (IV) dioxide (TiO₂) nanocomposites are presented in this paper. The results show that both polymers are susceptible to weathering degradation, but their degradation rates are different and are also influenced by the presence of TiO₂ in the samples. Visual, microscopic and atomic force microsocpy observations of the surface after accelerated weathering tests confirmed that degradation occurred faster in the PLA/PCL blends than in the PLA/PCL/TiO₂ nanocomposites. The X-ray diffraction results showed the degradation of PCL in the disappearance of its characteristic peaks over weathering time, and also confirmed that PLA lost its amorphous character and developed crystals from the shorter chains formed as a result of degradative chain scission. It was further observed that the presence of TiO₂ retarded the degradation of both PLA and PCL. These results were supported by the differential scanning calorimetry results. The thermogravimetric analysis results confirmed that that PLA and PCL respectively influenced each other's thermal degradation, and that TiO₂ played a role in the thermal degradation of both PLA and PCL. The tensile properties of both PLA/PCL and PLA/PCL/TiO₂ were significantly reduced through weathering exposure and the incorporation of TiO₂.     

Fabrication of hydroxyapatite blended cyclic type polylactic acid and poly (ε-caprolactone) tissue engineering scaffold

The ultimate goal of tissue engineering serves to repair, restore damaged tissue or organ due to accident or disease. In this research, we are aimed at investigating the feasibility of processing cyclic type polylactic acid (PDLLA)/poly(ε-caprolactone) (PCL)/hydroxyapatite (HA) biomaterial into tissue engineering scaffold (TES) with variable mechanical properties, well interconnected pore architecture, and controlled hydrophilicity. For this, an in-house built bone scaffold 3D printing (BS3P) system was applied to two biomaterials, namely PDLLA-PCL and HA-PCL. These two biomaterials were produced by optimizing the robotic control system. Morphological investigation by scanning electron microscope (SEM) revealed both TES formed by new materials able to show honeycomb-like architectures, excellent fusion at the filament junctions, high uniformity, complete interconnectivity, and controlled channel characteristics of the TES. Compression tests align with the typical behavior of a porous material undergoing deformation. In vitro cell culture study and confocal laser microscopy (CLM) showed enhanced cell adhesion, proliferation, and extracellular matrix (ECM) formation. The results demonstrated the eligibility of the BS3P system to produce TES, and the suitability of the new biomaterial scaffolds in enhancing cell biocompatibility.     

Mathematical Modeling of the Poly(lactic acid) Ring–Opening Polymerization Kinetics

The modeling of ring-opening polymerization of (D,L)-lactide to poly(lactic acid) (PLA) has been performed. Except some reported data on the apparent rate constant, there is lack of data in the literature on the rate constants for initiation, propagation and termination steps of PLA polymerization. Using a simple numerical technique, the individual rate constants are evaluated theoretically and the results are compared with the available experimental data for ring-opening polymerization of PLA. The proposed method works well without requiring a polymer chain length independent rate constant. It is also shown that presence of even small amount of impurity (e.g., water) in the reaction kettle can greatly limit the polymer molecular weight.     

Synthesis of hollow α-Fe2O3–silica composites templated by poly(acrylic acid) colloidal aggregates

The synthesis of inorganic hollow nanoparticles has attracted more and more attention in recent research. In this article, hollow α-Fe₂O₃–silica composites were synthesized by a modified Stöber method. Tetraethyl orthosilicate (TEOS) formed oil drops, and ammonia solution facilitated the hydrolysis polymerization of TEOS. In the hydrolysis process of TEOS, we used cetyltrimethylammonium bromide and poly(acrylic acid) colloidal aggregates as the surfactant and template, respectively. The diameters of the composites we obtained are about 20 and 180 nm, respectively, which are smaller than that of pure silica spheres (200 nm). Moreover, Brunauer–Emmett–Teller surface areas of hollow α-Fe₂O₃–silica composites were determined to be in the range of 377–498 m²/g, and their pore sizes are around 2 nm as were determined by BJH method. The mesoporous silica was successfully coated around the α-Fe₂O₃. The synthesis process of the composites is a simple, one-step route, which exhibits the potential need for a great amount of synthesis for future research.