A Comparative Study between Beeswax and Glycerol Monostearate for Food-Grade Oleogels.

With the aim to produce solid fats with a high percentage of unsaturated fatty acids, oleogels based on olive and peanut oil with different concentrations of beeswax (BW) and glycerol monostearate (GMS) as oleogelators were studied and compared. The critical oleogelator concentration for both BW and GMS was 3%. Thermal properties of the developed GMS-based oleogels pointed to a polymorphic structure, confirmed by the presence of two exothermic and endothermic peaks. All developed oleogels released less than 4% of oil, highlighting their high oil binding capacity. A morphology evaluation of oleogels showed platelet-like crystals, characterized by a cross-sectional length of 50 µm in BW-based oleogels and irregular clusters of needle-like crystals with a higher diameter in GMS-based oleogels. BW-based oleogels showed a solid fat content ranging from 1.16% to 2.27%, and no solid fat content was found at 37 °C. GMS-based oleogels reached slightly higher values of SFC that ranged from 1.58% to 2.97% at 25 °C and from 1.00% to 1.75% at 37 °C. Olive oil-based oleogels with GMS showed higher firmness compared with BW-based ones. The stronger structure network in olive oil/GMS-based oleogels provided a real physical barrier to oxidants, showing a high oxidation stability.

Morphology Distribution in Injection Molded Parts.

A more sustainable use of plastic parts makes it necessary to replace current plastic parts with recyclable components, also allowing the modulation of the part properties through the process. Injection molding is one of the most widely used technologies for obtaining rigid plastic parts, so it is crucial to understand how to tailor properties by adopting the correct processing conditions. One way is to perform annealing steps directly inside the mold: in-mold annealing improves the structural integrity and durability of the material, reduces defects, increases the resistance of parts against certain chemicals, reduces wear and tear, increases ductility, and lowers brittleness. In this work, several in-mold annealing steps were conducted, changing the mold temperature and annealing duration selected on the basis of the half crystallization time of the adopted isotactic polypropylene. The typical molded part morphology, composed of oriented layers at the surface, transition zones, and spherulitic core, is strongly affected by in-mold annealing. In particular, the thickness of the oriented layer, which forms in the early phase of the process, decreases, and the spherulites increase in size. Concerning mechanical behavior, the orientation degree mostly determines the elastic modulus value close to the surface, whereas the conditions under which crystallization occurs determine the modulus in the core.

Modulating poly(lactic acid) degradation rate for environmentally sustainable applications.

The huge amount of plastics generated by the massive use of packaging makes it difficult to manage waste safely. Introducing biodegradable polymers, such as poly(lactic acid) (PLA), can at least partially reduce the environmental pollution from plastic waste. Biodegradable polymers must have a degradation rate appropriate for the intended use to replace durable plastics. This work aims to introduce PLA fillers that can modulate the degradation rate during hydrolysis and composting. For this purpose, fumaric acid and magnesium hydroxide have been proposed. The experimental findings demonstrated that magnesium oxide makes hydrolysis faster than fumaric acid. A model describing the hydrolysis reaction, which also considers the effect of crystallinity, is proposed. The model can capture the filler effect on the kinetic constants related to the autocatalytic part of the hydrolysis reaction. Degradation of the PLA and compounds was also conducted in a composting medium. The compound with fumaric acid shows faster degradation than the compound with magnesium oxide; this behavior is opposite to what is observed during hydrolysis. Degradation in a composting medium is favored in a narrow pH window corresponding to the optimum environment for microorganism growth. Magnesium oxide leads to a pH increase above the optimum level, making the environment less favorable to microorganism growth. Vice-versa, fumaric acid maintains the pH level in the optimum range: it represents an additional carbon source for microorganism growth.

Analysis of Weld Lines in Micro-Injection Molding.

Micro-injection molding (µIM) is a widespread process for the production of plastic parts with at least one dimension, or feature, in the microscale (conventionally below 500 µm). Despite injection molding being recognized as a robust process for obtaining parts with high geometry accuracy, one last occurrence remains a challenge in micro-injection molding, especially when junctions are present on the parts: the so-called weld lines. As weld lines are crucial in determining mechanical part performances, it is mandatory to clarify weld line position and characteristics, especially at the industrial scale during mold design, to limit failure causes. Many works deal with weld lines and their dependence on processing parameters for conventional injection molding, but only a few works focus on the weld line in µIM. This work examines the influence of mold temperature on the weld line position and strength by both experimental and simulation approaches in µIM. At mold temperatures below 100 °C, only short shots were obtained in the chosen cavity. At increased mold temperatures, weld lines show up to a 40% decrease in the whole length, and the overall tensile modulus doubles. This finding can be attributed to the reduction of the orientation at the weld line location favored by high mold temperatures. Moldflow simulations consistently reproduce the main features of the process, weld line position and length. The discrepancy between experimental and simulated results was attributed to the fact that crystallization in flow conditions was not accounted for in the model.

Modeling and Analysis of Morphology of Injection Molding Polypropylene Parts Induced by In-Mold Annealing.

It is generally recognized that high-temperature treatments, namely annealing, influence the microstructure and the morphology, which, in turn, determine the mechanical properties of polymeric parts. Therefore, annealing can be adopted to control the mechanical performance of the molded parts. This work aims to assess the effect of annealing on the morphology developed in isotactic polypropylene (iPP) injection-molded parts. In particular, a two-step annealing is adopted: the polymer is injected in a mold at a high temperature (413 or 433 K), which is kept for 5 min (first annealing step); afterward, the mold temperature is cooled down at 403 K and held at that temperature for a time compatible with the crystallization half-time at that temperature (second annealing step). The characterization of morphology is carried out by optical and electronic scanning microscopy. The temperature of the first annealing step does not influence the thickness of the fibrillar skin layer; however, such a layer is thinner than that found in the molded parts obtained without any annealing steps. The second annealing step does not influence the thickness of the fibrillar skin layer. The dimension of spherulites found in the core is strongly influenced by both annealing steps: the spherulite dimensions enlarge by the effect of annealing steps. A model that considers spherulite and fibril evolutions is adopted to describe the effect of molding conditions on the final morphology distribution along the part thickness. The model, which adopts as input the thermo-mechanical histories calculated by commercial software for injection molding simulation, consistently predicts the main effects of the molding conditions on the morphology distributions.

Production of Mesoglycan/PCL Based Composites through Supercritical Impregnation.

The development of targeted therapies for wound repair is knowing a growing interest due to the increasing aging of the population and the incidence of chronic pathologies, mainly pressure ulcers. Among molecules recruiting cell populations and promoting the formation of new vital tissue, sodium mesoglycan (MSG) has been proven to be effective in wound healing. In this work, MSG impregnation of polymer matrices has been attempted by a supercritical carbon dioxide-based process. Polymeric matrices are composed of polycaprolactone blends, where water-soluble polymers, polyethylene glycol, polyvinyl pyrrolidone, gelatin, and thermoplastic starch, have been employed to modulate the MSG release, making the devices potentially suitable for topical administrations. Two different techniques have been used to obtain the films: the first one is compression molding, producing compact and continuous structures, and the second one is electrospinning, producing membrane-like designs. A higher amount of MSG can be loaded into the polymeric matrix in the membrane-like structures since, in these films, the impregnation process is faster than in the case of compression molded films, where the carbon dioxide has firstly diffused and then released the active molecule. The type of water-soluble polymer influences the drug release rate: the blend polycaprolactone-gelatin gives a prolonged release potentially suitable for topical administration.

Multi-Scale Simulation of Injection Molding Process with Micro-Features Replication: Relevance of Rheological Behaviour and Crystallization.

The possibility of tailoring key surface properties through the injection molding process makes it intriguing from the perspective of sustainability enhancement. The surface properties depend on the replication accuracy of micro and nanostructures on moldings; such an accuracy is enhanced with cavity temperature. The simulation of the injection molding process is very challenging in the presence of micro and nanostructures on the cavity surface; this does not allow for the neglect of phenomena generally considered not to influence the overall process. In this paper, a multiscale approach was proposed: in the first step, the simulation of the overall process was conducted without considering the presence of the microstructure; in the second step the outputs of the first step were used as an input to simulate the replication of the microfeature. To this purpose, a lubrication approximation was adopted, and the contribution of the trapped air, which slows down the polymer advancement, was accounted for. A modification of the viscosity equation was also proposed to describe the rheological behavior of isotactic polypropylene at very low temperatures. Concerning the microcavity filling simulation, the modification of the viscosity description at low temperatures consistently describes the process, in terms of polymer solidification. Concerning the replication accuracy, it increases with the cavity surface temperature, consistently with the experimental observations.

Polycaprolactone/polyethylene-glycol capsules made by injection molding: A drug release modeling.

Polycaprolactone (PCL)/Polyethylene-glycol (PEG) capsules are prepared by injection molding with the aim of producing Colon-specific Drug Delivery Systems (CDDS). PCL, being a gastroresistant polymer, is suitable for this kind of delivery; however, the release from PCL devices is too slow. For this reason, in this paper, different percentages of PEG (10, 20 and 30 w/w %) have been added to obtain blends able to modulate the release from PCL-based capsules. The drug release rate from PCL/PEG capsules increases with the PEG percentage; using PCL/PEG 70/30 w/w capsules, the drug release is suitable for CDDS. The experimental data have been modelled, accounting for three steps: the penetration of the release medium into the capsule, the drug dissolution in the release medium, and the drug migration from the capsule to the medium. The model accurately describes the data, showing a mass transfer coefficient strongly dependent on the PEG percentage.

Morphology-Mechanical Performance Relationship at the Micrometrical Level within Molded Polypropylene Obtained with Non-Symmetric Mold Temperature Conditioning.

The control of the structural properties of a polymeric material at the micro and nano-metrical scale is strategic to obtaining parts with high performance, durability and free from sudden failures. The characteristic skin-core morphology of injection molded samples is intimately linked to the complex shear flow, pressure and temperature evolutions experienced by the polymer chains during processing. An accurate analysis of this morphology can allow for the assessment of the quality and confidence of the process. Non-symmetric mold temperature conditions are imposed to produce complex morphologies in polypropylene parts. Morphological and micromechanical characterizations of the samples are used to quantify the effects of the processing conditions on the part performance. Asymmetric distribution of temperatures determines asymmetric distribution of both morphology and mechanical properties. The inhomogeneity degree depends on the time that one side of the cavity experiences high temperatures. The spherulites, which cover the thickest of the parts obtained with high temperatures at one cavity side, show smaller values of elastic modulus than the fibrils. When the polymer molecules experience high temperatures for long periods, the solid-diffusion and the partial melting and recrystallization phenomena determine a better structuring of the molecules with a parallel increase of the elastic modulus.

Alginate hydrogel: The influence of the hardening on the rheological behaviour.

Alginate based gels are widely adopted in many pharmaceutical and biomedical fields. The main rheological characteristics of the alginate-based gels are important design parameters for gel preparation. A new methodology for rheological tests on the alginate-based gels has been assessed in order to obtain reliable and reproducible results in terms of loss and storage moduli. The methodology accounts for the effect of morphology on the rheological properties. Reliable results can be achieved if the structure of the gel is preserved during the analysis, thus, the control of the load applied during the rheological test plays a crucial role. The application of the proposed methodology allows to obtain information about the cross-linking degree of hydrogels. To this purpose, hydrogels with different ratios of divalent cations and alginate have been adopted. The number of junctions in the network formed during the cross-linking process has been evaluated and the results are consistent with the infrared analysis conducted on the same hydrogels.

Fused Filament Deposition of PLA: The Role of Interlayer Adhesion in the Mechanical Performances.

A set of criteria to enhance mechanical performances of standard specimens (Type V, ANSI D368) made of polylactic acid (PLA) were proposed. Fused PLA deposition was conducted with nozzle temperature ranging from 180 to 230 °C and deposition plate temperature ranging from 70 to 110 °C. Optical microscopy, elastic modulus analysis and density measurement allowed emphasizing the effect of temperature field, also measured during the process, on the morphology and the mechanical characteristics of the specimen. Atomic force microscopy revealed a morphology typical of amorphous samples with globular structures. Poor interlayer adhesion was detected in the part of the specimen located at larger distance from the deposition plate, showing an elastic modulus lower than those measured in the central part (220 MPa vs. 500 MPa). The specimen crystallinity degree was below 3%. The molecular weight between entanglements was adopted as a measure of the interlayer molecular diffusion. A successful diffusion and re-entanglement of the polymer melt at the interface was the key to improving mechanical performance. A mathematical model describing the transient heat transfer during the fused PLA deposition and accounting for solidification and the nonisothermal crystallization kinetics was introduced. Simulated temperature evolutions were consistent with the experimental ones. They were related to the mechanical performances, the morphology, and the molecular weight between entanglements of the parts.

Correction: Speranza, V. et al. Hierarchical Structure of iPP During Injection Molding Process with Fast Mold Temperature Evolution. Materials 2019, 12, 424.

The correction reported in the following has to be applied to the paper [...].

Effect of Rapid Mold Heating on the Structure and Performance of Injection-Molded Polypropylene.

The tailoring by the process of the properties developed in the plastic objects is the more effective way to improve the sustainability of the plastic objects. The possibility to tailor to the final use the properties developed within the molded object requires further understanding of the relationship between the properties of the plastic objects and the process conduction. One of the main process parameters that allow adjusting the properties of molded objects is the mold temperature. In this work, a thin electrical heater was located below the cavity surface in order to obtain rapid and localized surface heating/cooling cycles during the injection molding process. An isotactic polypropylene was adopted for the molding tests, during which surface temperature was modulated in terms of values and heating times. The modulation of the cavity temperature was found able to control the distribution of relevant morphological characteristics, thus, properties along the sample thickness. In particular, lamellar thickness, crystallinity distribution, and orientation were analyzed by synchrotron X-ray experiments, and the morphology and elastic modulus were characterized by atomic force microscopy acquisitions carried out with a tool for the simultaneous nanomechanical characterization. The crystalline degree slightly increased with the cavity temperature, and this induced an increase in the elastic modulus when high temperatures were adopted for the cavity surface. The cavity temperature strongly influenced the orientation distribution that, on its turn, determined the highest values of the elastic modulus found in the shear layer. Furthermore, although the sample core, not experiencing a strong flow field, was not characterized by high levels of orientation, it might show high values of the elastic modulus if temperature and time during crystallization were sufficient. In particular, if the macromolecules spent adequate time at temperatures close to the crystallization temperature, they could achieve high levels of structuring and, thus, high values of elastic modulus.

PCL/Mesoglycan Devices Obtained by Supercritical Foaming and Impregnation.

In this work, a one-shot process for the simultaneous foaming of polycaprolactone (PCL) and impregnation of mesoglycan (MSG) into the porous structure was successfully attempted. Supercritical carbon dioxide plays the role of the foaming agent with respect to PCL and of the solvent with respect to MSG. The main objective is to produce an innovative topical device for application on skin lesions, promoting prolonged pro-resolving effects. The obtained device offers a protective barrier to ensure a favorable and sterilized environment for the wound healing process. The impregnation kinetics revealed that a pressure of 17 MPa, a temperature of 35 °C, and a time of impregnation of 24 h assured a proper foaming of PCL in addition to the impregnation of the maximum amount of MSG; i.e., 0.22 mgMSG/mgPCL. After a preliminary study conducted on PCL granules used as brought, the MSG impregnation was performed at the optimized process conditions also on a PCL film, produced by compression molding, with the final goal of producing medical patches. Comparing the dissolution profiles in phosphate buffered saline solution (PBS) of pure MSG and MSG impregnated on foamed PCL, it was demonstrated that the release of MSG was significantly prolonged up to 70 times. Next, we performed functional assays of in vitro wound healing, cell invasion, and angiogenesis to evaluate the biological effects of the PCL-derived MSG. Interestingly, we found the ability of this composite system to promote the activation of human keratinocytes, fibroblasts, and endothelial cells, as the main actors of tissue regeneration, confirming what we previously showed for the MSG alone.

Hierarchical Structure of iPP During Injection Molding Process with Fast Mold Temperature Evolution.

Mold surface temperature strongly influences the molecular orientation and morphology developed in injection molded samples. In this work, an isotactic polypropylene was injected into a rectangular mold, in which the cavity surface temperature was properly modulated during the process by an electrical heating device. The induced thermo-mechanical histories strongly influenced the morphology developed in the injection molded parts. Polarized optical microscope and atomic force microscope were adopted for morphological investigations. The combination of flow field and cooling rate experienced by the polymer determined the hierarchical structure. Under strong flow fields and high temperatures, a tightly packed structure, called shish-kebab, aligned along the flow direction, was observed. Under weak flow fields, the formation of ß-phase, as cylindrites form, was observed. The formation of each morphological structure was analyzed and discussed on the bases of the flow and temperature fields, experienced by the polymer during each stage of the injection molding process.

Process Induced Morphology Development of Isotactic Polypropylene on the Basis of Molecular Stretch and Mechanical Work Evolutions.

It is well known that under high shear rates polymers tend to solidify with formation of morphological elements oriented and aligned along the flow direction. On the other hand, stretched polymer chains may not have sufficient time to undergo the structuring steps, which give rise to fibrillar morphology. In the last decades, several authors have proposed a combined criterion based on both a critical shear rate and a critical mechanical work, which guaranties adequate time for molecular structuring. In this paper, the criterion, reformulated on the basis of critical values of both molecular stretch and mechanical work and adjusted to account for the unsteady character of the polymer processing operations, is applied to the analysis of a set of isotactic polypropylene injection molded samples obtained under very different thermal boundary conditions. The evolutions of molecular stretch and mechanical work are evaluated using process simulation. The results of the model reproduce the main characteristics of the morphology distribution detected on the cross sections of moldings, obtained under very different thermal boundary conditions, assuming that the critical work is a function of temperature.

Replication of Micro- and Nanofeatures in Injection Molding of Two PLA Grades with Rapid Surface-Temperature Modulation.

The production by injection molding of polymeric components having micro- and nanometrical surfaces is a complex task. Generally, the accurate replication of micro- and nanometrical features on the polymeric surface during the injection-molding process is prevented by of the low mold temperature adopted to reduce cooling time. In this work, we adopt a system that allows fast heating of the cavity surface during the time the melt reaches the cavity, and fast cooling after heater deactivation. A nickel insert with micro- and nanofeatures in relief is located on the cavity surface. Replication accuracy is analyzed by Atomic Force Microscopy under different injection-molding conditions. Two grades of polylactic acid with different viscosity have been adopted. The results indicate that the higher the cavity surface temperature is, the higher the replication accuracy is. The viscosity has a significant effect only in the replication of the microfeatures, whereas its effect results are negligible in the replication of nanofeatures, thus suggesting that the interfacial phenomena are more important for replication at a nanometric scale. The evolution of the crystallinity degree on the surface also results in a key factor on the replication of nanofeatures.

Hydrophobicity Tuning by the Fast Evolution of Mold Temperature during Injection Molding.

The surface topography of a molded part strongly affects its functional properties, such as hydrophobicity, cleaning capabilities, adhesion, biological defense and frictional resistance. In this paper, the possibility to tune and increase the hydrophobicity of a molded polymeric part was explored. An isotactic polypropylene was injection molded with fast cavity surface temperature evolutions, obtained adopting a specifically designed heating system layered below the cavity surface. The surface topology was characterized by atomic force microscopy (AFM) and, concerning of hydrophobicity, by measuring the water static contact angle. Results show that the hydrophobicity increases with both the temperature level and the time the cavity surface temperature was kept high. In particular, the contact angle of the molded sample was found to increase from 90°, with conventional molding conditions, up to 113° with 160 °C of cavity surface temperature kept for 18 s. This increase was found to be due to the presence of sub-micro and nano-structures characterized by high values of spatial frequencies which could be more accurately replicated by adopting high heating temperatures and times. The surface topography and the hydrophobicity resulted therefore tunable by selecting appropriate injection molding conditions.

Mechanical Properties Distribution within Polypropylene Injection Molded Samples: Effect of Mold Temperature under Uneven Thermal Conditions.

The quality of the polymer parts produced by injection molding is strongly affected by the processing conditions. Uncontrolled deviations from the proper process parameters could significantly affect both internal structure and final material properties. In this work, to mimic an uneven temperature field, a strong asymmetric heating is applied during the production of injection-molded polypropylene samples. The morphology of the samples is characterized by optical and atomic force microscopy (AFM), whereas the distribution of mechanical modulus at different scales is obtained by Indentation and HarmoniX AFM tests. Results clearly show that the temperature differences between the two mold surfaces significantly affect the morphology distributions of the molded parts. This is due to both the uneven temperature field evolutions and to the asymmetric flow field. The final mechanical property distributions are determined by competition between the local molecular stretch and the local structuring achieved during solidification. The cooling rate changes affect internal structures in terms of relaxation/reorganization levels and give rise to an asymmetric distribution of mechanical properties.

Design and production of gentamicin/dextrans microparticles by supercritical assisted atomisation for the treatment of wound bacterial infections.

In this work, the supercritical assisted atomisation (SAA) is proposed, for the first time, for the production of topical carrier microsystems based on alginate-pectin blend. Gentamicin sulphate (GS) was loaded as high soluble and hygroscopic antibiotic model with poor flowability. Particularly, different water solutions of GS/alginate/pectin were processed by SAA to produce spherical microparticles (GAP) of narrow size (about 2 µm). GS loading was varied between 20% and 33% (w/w) with an encapsulation efficiency reaching about 100%. The micronised powders also showed high flow properties, good stability and constant water content after 90 days in accelerated storage conditions. The release profiles of the encapsulated drug were monitored using vertical diffusion Franz cells to evaluate the application of GAP microsystems as self-consistent powder formulation or in specific fibres or gels for wound dressing. All formulations showed an initial burst effect in the first 6h of application (40-65% of GS loaded), and in particular GAP4 produced with a GS/alginate/pectin ratio of 1:3:1, exhibited the ability to release GS continuously over 6 days. Antimicrobial tests against Staphylococcus aureus indicated that GS antibiotic activity was preserved at 6 days and higher than pure GS at 12 and 24 days for all SAA formulations, especially for GAP1.