Shear-Induced and Nanofiber-Nucleated Crystallization of Novel Aliphatic–Aromatic Copolyesters Delineated for In Situ Generation of Biodegradable Nanocomposites

The shear-induced and cellulose-nanofiber nucleated crystallization of two novel aliphatic–aromatic copolyesters is outlined due to its significance for the in situ generation of biodegradable nanocomposites, which require the crystallization of nanofibrous sheared inclusions at higher temperatures. The shear-induced non-isothermal crystallization of two copolyesters, namely, poly(butylene adipate-co-succinate-co-glutarate-co-terephthalate) (PBASGT) and poly(butylene adipate-co-terephthalate) (PBAT), was studied following a light depolarization technique. To have a deep insight into the process, the effects of the shear rate, shear time, shearing temperature and cooling rate on the initiation, kinetics, growth and termination of crystals were investigated. Films of 60 μm were subjected to various shear rates (100–800 s−1) for different time intervals during cooling. The effects of the shearing time and increasing the shear rate were found to be an elevated crystallization temperature, increased nucleation density, reduced growth size of lamella stacks and decreased crystallization time. Due to the boosted nucleation sites, the nuclei impinged with each other quickly and growth was hindered. The effect of the cooling rate was more significant at lower shear rates. Shearing the samples at lower temperatures, but still above the nominal melting point, further shifted the non-isothermal crystallization to higher temperatures. As a result of cellulose nanofibers’ presence, the crystallization of PBAT, analyzed by DSC, was shifted to higher temperatures.

Development of novel biodegradable nanocomposites for bone repair applications

The main goal of this research is to introduce novel series of biodegradable nanocomposites that closely mimic the characteristics of real bone such as mechanical and thermal properties. These nanocomposites are composed of cotton-sourced cellulose microcrystals (MCC), hydroxyapatite nanoparticles (HA) and Poly L-Lactic Acid (PLLA). A novel fabrication route is used to manufacture MA and MH series of nanocomposites. MA series was developed to find an optimum range for weight fraction of each constituent required for design of the MH series. Evaluation of the thermal properties of MA series showed that increasing of weight ratio of MCC and HA from 0 to 21 Wt% increased the crystallinity up to 38%. Compression test results of them revealed that increasing the weight fraction of MCC or HA from 0 to 21Wt% enhanced the compressive yield stress from 0.127 to 2.2 MPa and the Young’s modulus from 6.6 to 38 MPa. The cytotoxicity assay results showed there was no sign of toxic material affecting on viability of cells. The MH series was designed and fabricated by selecting a narrower range of weight fraction of the constituents. A design of experiments was used to alter the composition of the constituents to assess their contributions and their effect onto the mechanical properties and biodegradation behaviour of the MH series of the nanocomposites. The weight ratio of MCC to HA, the concentration of PLLA, and the porogen content were chosen as varying factors. A model that accurately predicts the optimum parameter setting was created. Analysis of variance statistical analysis showed that the ratio of MCC to HA was the most influential factor affecting the compressive yield and the mass loss, while the porogen content was the most detrimental factor affecting the Young’s modulus of MH series of nanocomposites had no significant effect on their rate of the mass loss. The nanocomposites with highest weight ratio 4 of MCC to HA, showed maximum mechanical strength and the lowest water absorption and the lowest mass loss. It was found two series of nanocomposites was comparable to trabecular bone from a compositional, structural, thermal, mechanical point of view.

Development of novel biodegradable nanocomposites for bone repair applications

The main goal of this research is to introduce novel series of biodegradable nanocomposites that closely mimic the characteristics of real bone such as mechanical and thermal properties. These nanocomposites are composed of cotton-sourced cellulose microcrystals (MCC), hydroxyapatite nanoparticles (HA) and Poly L-Lactic Acid (PLLA). A novel fabrication route is used to manufacture MA and MH series of nanocomposites. MA series was developed to find an optimum range for weight fraction of each constituent required for design of the MH series. Evaluation of the thermal properties of MA series showed that increasing of weight ratio of MCC and HA from 0 to 21 Wt% increased the crystallinity up to 38%. Compression test results of them revealed that increasing the weight fraction of MCC or HA from 0 to 21Wt% enhanced the compressive yield stress from 0.127 to 2.2 MPa and the Young’s modulus from 6.6 to 38 MPa. The cytotoxicity assay results showed there was no sign of toxic material affecting on viability of cells. The MH series was designed and fabricated by selecting a narrower range of weight fraction of the constituents. A design of experiments was used to alter the composition of the constituents to assess their contributions and their effect onto the mechanical properties and biodegradation behaviour of the MH series of the nanocomposites. The weight ratio of MCC to HA, the concentration of PLLA, and the porogen content were chosen as varying factors. A model that accurately predicts the optimum parameter setting was created. Analysis of variance statistical analysis showed that the ratio of MCC to HA was the most influential factor affecting the compressive yield and the mass loss, while the porogen content was the most detrimental factor affecting the Young’s modulus of MH series of nanocomposites had no significant effect on their rate of the mass loss. The nanocomposites with highest weight ratio 4 of MCC to HA, showed maximum mechanical strength and the lowest water absorption and the lowest mass loss. It was found two series of nanocomposites was comparable to trabecular bone from a compositional, structural, thermal, mechanical point of view.

Synthesis and physical properties of biodegradable nanocomposites fabricated using acrylic acid-grafted poly(butylene carbonate-co-terephthalate) and organically-modified layered zinc phenylphosphonate

A set of novel biocompatible aliphatic-aromatic nanocomposites, including numerous acrylic acid-grafted poly(butylene carbonate-co-terephthalate) (g-PBCT) and organically-modified layered zinc phenylphosphonate (m-PPZn), were successfully synthesized via polycondensation and transesterification. A primary covalent linkage was produced between the biocompatible polymer and the inorganic reinforcements. Fourier transform infrared spectroscopy and 13C-nuclear magnetic resonance spectra demonstrated the successful grafting of acrylic acid into the PBCT (g-PBCT). Both wide-angle X-ray diffraction data and X-ray photoelectron spectroscopy analysis showed that the g-PBCT polymer matrix was intercalated into the interlayer spacing of the m-PPZn and was chemically interacted with the m-PPZn. The addition of m-PPZn in the g-PBCT matrix significantly improved its storage modulus. A slight increase in thermal stability was observed in all the g-PBCT/m-PPZn composites. Both results are attributed to the presence of covalent bond between g-PBCT and m-PPZn.