Reactive processing-microstructure-mechanical performance correlations in biodegradable poly(lactic acid)/expanded graphite nanocomposites.

Reactive extrusion is a promising method to prepare biodegradable nanocomposites with enhanced modulus, strength and toughness. In this study, biodegradable extended nanocomposites based on poly(lactic acid) (PLA)/expanded graphite (EG) were prepared by melt-compounding using a co-rotating twin-screw extruder. Effects of EG loading, aspect ratio, delamination and dispersion state on the mechanical and thermo-mechanical properties of PLA/EG nanocomposites were investigated. Adding the largest EG (EGL) nanoplatelets, having the average particle size of 48.2 µm and aspect ratio of 19.5, to the PLA matrix enhanced the Young modulus, tensile strength, ultimate strain and tensile toughness of the extended PLA sample with benzoyl peroxide (BP) between 40-100%. The observed enhancements originated from restricted PLA molecular motions, assisted PLA crystallization and intensified BP activity in extending the PLA chains. In contrast, EG nanofiller (EGS), with the lowest aspect ratio and size, lowered the PLA relaxation time and accelerated the PLA crystallization. This type of EG showed the weakest reinforcing effect on PLA. For the EG type (EGM) with an intermediate size and aspect ratio, it was observed that the presence of the nanoparticles had a negligible effect on the PLA molecular dynamic and reduced the PLA crystallization rate. The highest impact strength was observed for the PLA/EGM nanocomposite at 1 phr loading.

Extruded biocomposite films based on poly(lactic acid)/chemically-modified agricultural waste: Tailoring interface to enhance performance.

In this work, a lignocellulosic filler, rice straw (RS), was thermoplasticized by acetylation modification process and compounded with plasticized poly(lactic acid) (PLA) through twin-screw extrusion process. The biocomposite films were prepared continuously by using a slit die for PLA/RS and PLA/acetylated RS (ARS) compounds. By the chemical reaction, thermoset microstructure of RS was changed to a more flexible one. Additionally, by the reaction, the interfacial adhesion of lignocellulosic filler/PLA matrix, filler hydrophobicity and PLA wettability was enhanced considerably. The miscibility of partially phase-separated PLA/poly(ethylene glycol) (PEG) mixtures was improved by adding RS-based microfillers, particularly by the acetylated RS. Compared with PLA/unmodified RS films, PLA/ARS biocomposites show better thermal stability, toughness, Young modulus and softening point, especially at certain filler loadings.

A Novel Approach for Development of Intraocular Biodegradable Ranibizumab Implant: A Solution for Stability of Protein Activity.

Purpose: Ranibizumab is a monoclonal antibody fragment, targeting all isoforms of vascular endothelial growth factor A (VEGF-A), a protein involved in angiogenesis. It is used to treat age-related macular degeneration (AMD), retinal vein occlusion (RVO), and diabetic macular edema (DME), which are associated with blindness worldwide. However, proper treatment can decrease the loss of vision in about 90% of patients. Because of poor drug uptake in topical therapy and several adverse side effects of systemic irregularities and intravitreal injections, sustained-release drug delivery systems are more suitable for treatment. However, there are many challenges in the development of these systems due to the loss of protein activities. Methods: After drug complexation by the ion pairing method and preparation of a polymeric implant, containing the drug, the characteristics of the complexes were examined by Fourier-transform infrared spectroscopy and circular dichroism spectroscopy. The stability of antibody activity and biocompatibility of the released drug from the implant were assessed by bioassays and MTT assay, respectively. Finally, the release kinetics were investigated. Results: The bioassays showed the higher activity of the drug complex, compared to the free form, besides good biocompatibility in vitro. Also, the release data confirmed sustained and controlled release characteristics for the prepared implant. Conclusion: In this study, for the first time, we proposed a method for developing a sustained-release intraocular implant, consisting of ranibizumab by the heating method. This method allows for the industrial production of ranibizumab by extrusion and eliminates the complications related to reservoir systems.

An insight into different phenomena involved in continuous extrusion foaming of biodegradable poly(lactic acid)/expanded graphite nanocomposites.

The continuous extrusion foaming of poly(lactic acid) (PLA) has several critical drawbacks that crucially limit the substitution of the renewable foams for the extruded foams based on synthetic plastics. In this work, the foamability of PLA melt through a twin-screw extrusion process was improved by using expanded graphite (EG) nanoplatelets having different aspect ratios and loadings along with an organic peroxide. Morphological observations demonstrated the beneficial influences of adding nanofiller, which resulted in the formation of microcellular foams with larger void content and cell densities. Different phenomena, which are involved in the extrusion foaming of PLA melt, are considerably affected by the presence of EG including rheological behavior, PLA crystallization, thermal chain scission of the matrix, chain extension function of the peroxide and thermal decomposition of foaming agent. To correlate the phenomena affected by EG nanofiller with foam morphology, the linear viscoelastic responses, molecular weight, crystallization kinetics and structural properties of PLA and PLA/EG nanocomposites were evaluated.

Plasticized starch-based biocomposites containing modified rice straw fillers with thermoplastic, thermoset-like and thermoset chemical structures.

In this work, rice straw (RS) as an abundant biomass was applied to prepare some renewable thermoplastic materials by using soda-pulping and benzylation processes. The obtained RS products including untreated RS, RS pulp, benzylated RS pulp and pulping liquor as well as benzylated RS were incorporated into the thermoplastic starch through a twin-screw extrusion process to obtain all green composites. The successful thermoplasticization reaction of RS products was confirmed by spectroscopy results and morphological observations. The interfacial adhesion between the plasticized starch matrix and the RS products is enhanced by the chemical modifications, which confirmed by investigating through the morphological observations and linear rheological responses. The partial phase miscibility of the plasticizer/starch mixtures is improved by adding the benzylated RS and RS pulp. The RS pulp having cellulosic microfibers enhances the Young modulus and tensile strength of the plasticized starch even more than untreated RS. However, their thermoset and thermoset-like structure leads to the brittle failure mode of the starch biocomposites, similar to the common natural fiber biocomposites. The thermoplasticization reaction changes the failure mode and significantly improves the toughness of the plasticized starch/RS product biocomposites owing to better phase miscibility.

Controlled grafting of vinylic monomers on polyolefins: a robust mathematical modeling approach.

Experimental and mathematical modeling analyses were used for controlling melt free-radical grafting of vinylic monomers on polyolefins and, thereby, reducing the disturbance of undesired cross-linking of polyolefins. Response surface, desirability function, and artificial intelligence methodologies were blended to modeling/optimization of grafting reaction in terms of vinylic monomer content, peroxide initiator concentration, and melt-processing time. An in-house code was developed based on artificial neural network that learns and mimics processing torque and grafting of glycidyl methacrylate (GMA) typical vinylic monomer on high-density polyethylene (HDPE). Application of response surface and desirability function enabled concurrent optimization of processing torque and GMA grafting on HDPE, through which we quantified for the first time competition between parallel reactions taking place during melt processing: (i) desirable grafting of GMA on HDPE; (ii) undesirable cross-linking of HDPE. The proposed robust mathematical modeling approach can precisely learn the behavior of grafting reaction of vinylic monomers on polyolefins and be placed into practice in finding exact operating condition needed for efficient grafting of reactive monomers on polyolefins.