Phase Morphology and Mechanical Properties of Super-Tough PLLA/TPE/EMA-GMA Ternary Blends.

The inherent brittleness of poly(lactic acid) (PLA) limits its use in a wider range of applications that require plastic deformation at higher stress levels. To overcome this, a series of poly(l-lactic acid) (PLLA)/biodegradable thermoplastic polyester elastomer (TPE) blends and their ternary blends with an ethylene-methyl acrylate-glycidyl methacrylate (EMA-GMA) copolymer as a compatibilizer were prepared via melt blending to improve the poor impact strength and low ductility of PLAs. The thermal behavior, crystallinity, and miscibility of the binary and ternary blends were analyzed by differential scanning calorimetry (DSC). Tensile tests revealed a brittle-ductile transition when the binary PLLA/20TPE blend was compatibilized by 8.6 wt. % EMA-GMA, and the elongation at break increased from 10.9% to 227%. The "super tough" behavior of the PLLA/30TPE/12.9EMA-GMA ternary blend with the incomplete break and notched impact strength of 89.2 kJ∙m-2 was observed at an ambient temperature (23 °C). In addition, unnotched PLLA/40TPE samples showed a tremendous improvement in crack initiation resistance at sub-zero test conditions (-40 °C) with an impact strength of 178.1 kJ∙m-2. Morphological observation by scanning electron microscopy (SEM) indicates that EMA-GMA is preferentially located at the PLLA/TPE interphase, where it is partially incorporated into the matrix and partially encapsulates the TPE. The excellent combination of good interfacial adhesion, debonding cavitation, and subsequent matrix shear yielding worked synergistically with the phase transition from sea-island to co-continuous morphology to form an interesting super-toughening mechanism.

Degradation of Polylactic Acid Polymer and Biocomposites Exposed to Controlled Climatic Ageing: Mechanical and Thermal Properties and Structure.

This paper deals with the study of the degradation of polylactic acid (PLA) material structures and biocomposite systems with a PLA matrix containing ground natural particulate waste fillers, buckwheat husks and egg shells. Waste fillers were used without difficult cleaning operations to describe the effect of the raw waste material on PLA. Biocomposites with raw waste materials are increasingly coming to the forefront in car interiors and packaging products. The prepared material systems were exposed to controlled climatic ageing simulating long-term solar radiation and cyclic outdoor conditions. The degradation of the biocomposite systems was evaluated via thermal (differential scanning calorimetry) and mechanical properties (tensile and flexural tests, Charpy impact toughness). In addition to evaluating the degradation of the material structures using standardized tests, the influence and effect of controlled climatic ageing was visually assessed using SEM images (electron microscopy) of the surfaces and fracture surfaces of the test specimens.

Adipose-Derived Stem Cells in Reinforced Collagen Gel: A Comparison between Two Approaches to Differentiation towards Smooth Muscle Cells.

Scaffolds made of degradable polymers, such as collagen, polyesters or polysaccharides, are promising matrices for fabrication of bioartificial vascular grafts or patches. In this study, collagen isolated from porcine skin was processed into a gel, reinforced with collagen particles and with incorporated adipose tissue-derived stem cells (ASCs). The cell-material constructs were then incubated in a DMEM medium with 2% of FS (DMEM_part), with added polyvinylalcohol nanofibers (PVA_part sample), and for ASCs differentiation towards smooth muscle cells (SMCs), the medium was supplemented either with human platelet lysate released from PVA nanofibers (PVA_PL_part) or with TGF-ß1 + BMP-4 (TGF + BMP_part). The constructs were further endothelialised with human umbilical vein endothelial cells (ECs). The immunofluorescence staining of alpha-actin and calponin, and von Willebrand factor, was performed. The proteins involved in cell differentiation, the extracellular matrix (ECM) proteins, and ECM remodelling proteins were evaluated by mass spectrometry on day 12 of culture. Mechanical properties of the gels with ASCs were measured via an unconfined compression test on day 5. Gels evinced limited planar shrinkage, but it was higher in endothelialised TGF + BMP_part gel. Both PVA_PL_part samples and TGF + BMP_part samples supported ASC growth and differentiation towards SMCs, but only PVA_PL_part supported homogeneous endothelialisation. Young modulus of elasticity increased in all samples compared to day 0, and PVA_PL_part gel evinced a slightly higher ratio of elastic energy. The results suggest that PVA_PL_part collagen construct has the highest potential to remodel into a functional vascular wall.

The Injection Molding of Biodegradable Polydioxanone-A Study of the Dependence of the Structural and Mechanical Properties on Thermal Processing Conditions.

Recent years have observed a significant increase in the use of degradable materials in medicine due to their minimal impact on the patient and broad range of applicability. The biodegradable polymer Polydioxanone (PDO) provides a good example of the use of such one polymer that can represent the aforementioned medical materials in the field of medicine, due to its high level of biocompatibility and interesting mechanical properties. PDO is used to produce absorbable medical devices such as sutures and stents, and is also suitable for the fabrication of certain orthopedic implants. Polydioxanone can be processed using the injection molding method due to its thermoplastic nature; this method allows for the precise and easily-controllable production of medical materials without the need for toxic additives. A number of small commercial polymer implants have recently been introduced onto the market based on this processing method. It is important to note that, to date, no relevant information on the molding of PDO is available either for the scientific or the general public, and no study has been published that describes the potential of the injection molding of PDO. Hence, we present our research on the basic technological and material parameters that allow for the processing of PDO using the laboratory microinjection molding method. In addition to determining the basic parameters of the process, the research also focused on the study of the structural and mechanical properties of samples based on the thermal conditions during processing. A technological frame work was successfully determined for the processing of PDO via the microinjection molding approach that allows for the production of samples with the required homogeneity, shape stability and surface quality in a laboratory scale. The research revealed that PDO is a polymer with a major share of crystalline phases, and that it is sensitive to the annealing temperature profile in the mold, which has the potential to impact the final crystalline structure, the fracture morphology and the mechanical properties.

The Physical Properties and Crystallization Kinetics of Biocomposite Films Based on PLLA and Spent Coffee Grounds.

In the context of today's needs for environmental sustainability, it is important to develop new materials that are based on renewable resources and biodegrade at the end of their life. Bioplastics reinforced by agricultural waste have the potential to cause a revolution in many industrial applications. This paper reports the physical properties and crystallization kinetics of biocomposite films based on poly(L-lactic acid) (PLLA) and 10 wt.% of spent coffee grounds (SCG). To enhance adhesion between the PLLA matrix and SCG particles, a compatibilizing agent based on itaconic anhydride (IA)-grafted PLLA (PLLA-g-IA) was prepared by reactive extrusion using dicumyl peroxide (DCP). Furthermore, due to the intended application of the film in the packaging industry, the organic plasticizer acetyl tributyl citrate (ATBC) is used to improve processing and increase ductility. The crystallization behavior and thermal properties were observed by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). Crystallinity degree increased from 3,5 (neat PLLA) up to 48% (PLLA/PLLA-g-IA/ATBC/SCG) at the highest cooling rate. The physical properties were evaluated by tensile testing and dynamic mechanical analysis (DMA). The combination of the compatibilizer, SCG, and ATBC led to a synergistic effect that positively influenced the supramolecular structure, internal damping, and overall ductility of the composite films.

The Influence of Additives and Environment on Biodegradation of PHBV Biocomposites.

The biodegradation of polyhydroxybutyrate-co-hydroxyvalerate (PHBV) ternary biocomposites containing nature-based plasticizer acetyl tributyl citrate (ATBC), heterogeneous nucleation agents-calcium carbonate (CaCO3) and spray-dried lignin-coated cellulose nanocrystals (L-CNC)-in vermicomposting, freshwater biotope, and thermophilic composting have been studied. The degree of disintegration, differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and the evaluation of surface images taken by scanning electron microscopy (SEM) were conducted for the determination influence of different environments and additives on the biodegradation of PHBV. Furthermore, the method adapted from ISO 14855-1 standard was used for thermophilic composting. It is a method based on the measurement of the amount of carbon dioxide evolved during microbial degradation. The highest biodegradation rate was observed in the thermophilic condition of composting. The biodegradation level of all PHBV-based samples was, after 90 days, higher than 90%. Different mechanisms of degradation and consequently different degradation rate were evaluated in vermicomposting and freshwater biotope. The surface enzymatic degradation, observed during the vermicomposting process, showed slightly higher biodegradation potential than the hydrolytic attack of freshwater biotope. The application of ATBC plasticizers in the PHBV matrix caused an increase in biodegradation rate in all environments. However, the highest biodegradation rate was achieved for ternary PHBV biocomposites containing 10 wt. % of ATBC and 10 wt. % of CaCO3. A considerable increase in the degree of disintegration was evaluated, even in freshwater biotope. Furthermore, the slight inhibition effect of L-CNC on the biodegradation process of ternary PHBV/ATBC/L-CNC could be stated.

The Influence of Plasticizers and Accelerated Ageing on Biodegradation of PLA under Controlled Composting Conditions.

The overall performance of plasticizers on common mechanical and physical properties, as well as on the processability of polylactic acid (PLA) films, is well-explored. However, the influence of plasticizers on biodegradation is still in its infancy. In this study, the influence of natural-based dicarboxylic acid-based ester plasticizers (MC2178 and MC2192), acetyl tributyl citrate (ATBC Citroflex A4), and polyethylene glycol (PEG 400) on the biodegradation of extruded PLA films was evaluated. Furthermore, the influence of accelerated ageing on the performance properties and biodegradation of films was further investigated. The biodegradation of films was determined under controlled thermophilic composting conditions (ISO 14855-1). Apart from respirometry, an evaluation of the degree of disintegration, differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FT-IR), and scanning electron microscopy (SEM) of film surfaces was conducted. The influence of melt-processing with plasticizers has a significant effect on structural changes. Especially, the degree of crystallinity has been found to be a major factor which affects the biodegradation rate. The lowest biodegradation rates have been evaluated for films plasticized with PEG 400. These lower molecular weight plasticizers enhanced the crystallinity degrees of the PLA phase due to an increase in chain mobility. On the contrary, the highest biodegradation rate was found for films plasticized with MC2192, which has a higher molecular weight and evoked minimal structural changes of the PLA. From the evaluated results, it could also be stated that migration of plasticizers, physical ageing, and chain scission of films prompted by ageing significantly influenced both the mechanical and thermal properties, as well as the biodegradation rate. Therefore, the ageing of parts has to be taken into consideration for the proper evolution of the biodegradation of plasticized PLA and their applications.

Physical Properties and Non-Isothermal Crystallisation Kinetics of Primary Mechanically Recycled Poly(l-lactic acid) and Poly(3-hydroxybutyrate-co-3-hydroxyvalerate).

The physical properties and non-isothermal melt- and cold-crystallisation kinetics of poly (l-lactic acid) (PLLA) and poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) biobased polymers reprocessed by mechanical milling of moulded specimens and followed injection moulding with up to seven recycling cycles are investigated. Non-isothermal crystallisation kinetics are evaluated by the half-time of crystallisation and a procedure based on the mathematical treatment of DSC cumulative crystallisation curves at their inflection point (Kratochvil-Kelnar method). Thermomechanical recycling of PLLA raised structural changes that resulted in an increase in melt flow properties by up to six times, a decrease in the thermal stability by up to 80 °C, a reduction in the melt half-time crystallisation by up to about 40%, an increase in the melt crystallisation start temperature, and an increase in the maximum melt crystallisation rate (up to 2.7 times). Furthermore, reprocessing after the first recycling cycle caused the elimination of cold crystallisation when cooling at a slow rate. These structural changes also lowered the cold crystallisation temperature without impacting the maximum cold crystallisation rate. The structural changes of reprocessed PHBV had no significant effect on the non-isothermal crystallisation kinetics of this material. Additionally, the thermomechanical behaviour of reprocessed PHBV indicates that the technological waste of this biopolymer is suitable for recycling as a reusable additive to the virgin polymer matrix. In the case of reprocessed PLLA, on the other hand, a significant decrease in tensile and flexural strength (by 22% and 46%, respectively) was detected, which reflected changes within the biobased polymer structure. Apart from the elastic modulus, all the other thermomechanical properties of PLLA dropped down with an increasing level of recycling.

Effect of In-Mold Annealing on the Properties of Asymmetric Poly(l-lactide)/Poly(d-lactide) Blends Incorporated with Nanohydroxyapatite.

The proper choice of a material system for bioresorbable synthetic bone graft substitutes imposes strict requirements for mechanical properties, bioactivity, biocompatibility, and osteoconductivity. This study aims to characterize the effect of in-mold annealing on the properties of nanocomposite systems based on asymmetric poly(l-lactide) (PLLA)/Poly(d-lactide) (PDLA) blends at 5 wt.% PDLA loading, which was incorporated with nano-hydroxyapatite (HA) at various concentrations (1, 5, 10, 15 wt.%). Samples were melt-blended and injection molded into "cold" mold (50 °C) and hot mold (100 °C). The results showed that the tensile modulus, crystallinity, and thermal-resistance were enhanced with increasing content of HA and blending with 5 wt.% of PDLA. In-mold annealing further improved the properties mentioned above by achieving a higher degree of crystallinity. In-mold annealed PLLA/5PDLA/15HA samples showed an increase of crystallinity by ~59%, tensile modulus by ~28%, and VST by ~44% when compared to neat hot molded PLLA. On the other hand, the % elongation values at break as well as tensile strength of the PLLA and asymmetric nanocomposites were lowered with increasing HA content and in-mold annealing. Moreover, in-mold annealing of asymmetric blends and related nanocomposites caused the embrittlement of material systems. Impact toughness, when compared to neat cold molded PLLA, was improved by ~44% with in-mold annealing of PLLA/1HA. Furthermore, fracture morphology revealed fine dispersion and distribution of HA at 1 wt.% concentration. On the other hand, HA at a high concentration of 15 wt.% show agglomerates that worked as stress concentrators during impact loading.

Biodegradation of Poly(Lactic Acid) Biocomposites under Controlled Composting Conditions and Freshwater Biotope.

The influence of additives such as natural-based plasticiser acetyl tributyl citrate (ATBC), CaCO3 and lignin-coated cellulose nanocrystals (L-CNC) on the biodegradation of polylactic acid (PLA) biocomposites was studied by monitoring microbial metabolic activity through respirometry. Ternary biocomposites and control samples were processed by a twin-screw extruder equipped with a flat film die. Commonly available compost was used for the determination of the ultimate aerobic biodegradability of PLA biocomposites under controlled composting conditions (ISO 14855-1). In addition, the hydro-degradability of prepared films in a freshwater biotope was analysed. To determine the efficiency of hydro-degradation, qualitative analyses (SEM, DSC, TGA and FTIR) were conducted. The results showed obvious differences in the degradation rate of PLA biocomposites. The application of ATBC at 10 wt.% loading increased the biodegradation rate of PLA. The addition of 10 wt.% of CaCO3 into the plasticised PLA matrix ensured an even higher degradation rate at aerobic thermophilic composting conditions. In such samples (PLA/ATBC/CaCO3), 94% biodegradation in 60 days was observed. In contrast, neat PLA exposed to the same conditions achieved only 16% biodegradation. Slightly inhibited microorganism activity was also observed for ternary PLA biocomposites containing L-CNC (1 wt.% loading). The results of qualitative analyses of degradation in a freshwater biotope confirmed increased biodegradation potential of ternary biocomposites containing both CaCO3 and ATBC. Significant differences in the chemical and structural compositions of PLA biocomposites were found in the evaluated period of three months.

Application of Physical Methods for the Detection of a Thermally Degraded Recycled Material in Plastic Parts Made of Polypropylene Copolymer.

The paper deals with the possibility of applying physical methods to detect a thermally degraded recycled material in plastic parts made of polypropylene. Standard methods of evaluating the mechanical properties of the material under static tensile and bending stress, as well as under dynamic impact stress using the Charpy method, were used for the experimental measurements. The rheological properties of materials were monitored using a method involving measuring the melt flow index, while their thermal properties and oxidative stability were monitored using differential scanning calorimetry. Based on the methods used, it can be clearly stated that the most suitable technique for detecting thermally degraded recycled material in polypropylene is the method involving establishing the melt flow index. The bending test seems to be the most suitable method for detecting recycled material by measuring the material's mechanical properties. Similarly to the melt volume flow rate (MVR) method, it was possible to unambiguously detect the presence of even a small amount of recycled material in the whole from measuring the material's bending properties. It is clear from the results that in the short term, there may be no change in the useful properties of the parts, but in the long term the presence of degraded recycled material will have adverse consequences on their lifespan.

Effect of Radiation Crosslinking and Surface Modification of Cellulose Fibers on Properties and Characterization of Biopolymer Composites.

Recently, polymers have become the fastest growing and most widely used material in a huge number of applications in almost all areas of industry. In addition to standard polymer composites with synthetic matrices, biopolymer composites based on PLA and PHB matrices filled with fibers of plant origin are now increasingly being used in selected advanced industrial applications. The article deals with the evaluation of the influence and effect of the type of surface modification of cellulose fibers using physical methods (low-temperature plasma and ozone application) and chemical methods (acetylation) on the final properties of biopolymer composites. In addition to the surface modification of natural fibers, an additional modification of biocomposite structural systems by radiation crosslinking using gamma radiation was also used. The components of the biopolymer composite were a matrix of PLA and PHBV and the filler was natural cellulose fibers in a constant percentage volume of 20%. Test specimens were made from compounds of prepared biopolymer structures, on which selected tests had been performed to evaluate the properties and mechanical characterization of biopolymer composites. Electron microscopy was used to evaluate the failure and characterization of fracture surfaces of biocomposites.

Impact of Various Sterilization and Disinfection Techniques on Electrospun Poly-ε-caprolactone.

Electrospun materials made from biodegradable polycaprolactone are used widely in various tissue engineering and regenerative medicine applications because of their morphological similarity to the extracellular matrix. However, the main prerequisite for the use of such materials in clinical practice consists of the selection of the appropriate sterilization technique. This study is devoted to the study of the impact of traditional sterilization and disinfection methods on a nanofibrous polycaprolactone layer constructed by means of the needleless electrospinning technique. It was determined that hydrogen peroxide plasma treatment led to the loss of fibrous morphology and the creation of a foil. However, certain sterilization (ethylene oxide, gamma irradiation, and peracetic acid) and disinfection techniques (ethanol and UV irradiation) were found not to lead to a change in morphology; thus, the study investigates their impact on thermal properties, molecular weight, and interactions with a fibroblast cell line. It was determined that the surface properties that guide cell adhesion and proliferation were affected more than the bulk properties. The highest proliferation rate of fibroblasts seeded on nanofibrous scaffolds was observed with respect to gamma-irradiated polycaprolactone, while the lowest proliferation rate was observed following ethylene oxide sterilization.

Recycling of sisal fiber reinforced polypropylene and polylactic acid composites: Thermo-mechanical properties, morphology, and water absorption behavior.

The effect of recycling on the thermo-mechanical and water absorption behavior of polypropylene (PP)/sisal fiber and polylactic acid (PLA)/sisal fiber composites were studied. The PP-based non-biodegradable composites and PLA-based biodegradable composites were recycled for four times. The effect of recycling was determined by examining the morphology, thermo-mechanical properties, and water absorption behavior and the obtained results were compared. The results showed that the incorporation of sisal fibers in the PP and PLA matrix enhances the tensile modulus and percentage crystallinity of the composites. The tensile strength and modulus of the sisal fiber reinforced PP composites were not affected with recycling. Even though the tensile properties of PLA and PLA/sisal fiber reinforced composites are superior to PP and PP/sisal fiber composites, the PLA-based composites show a dramatic decrease in tensile strength and modulus after the first recycling due to the degradation of the polymer. The thermal stability of the PP/sisal fiber composites was not affected by the repeated recycling process. On the other hand, the PLA-based composites with higher sisal fiber content show a bit lower thermal stability after recycling. The PP-based composites show fluctuations in percentage crystallinity with recycling. On the other hand, a remarkable increase in percentage crystallinity for PLA and PLA-based composites was observed with increasing recycling times. Water diffusion study divulges that the diffusion of water into the polymer composites was reduced with recycling, irrespective of the polymer matrix.