Rambutan peel: An unconventional source of lignin and its potential applications in polymer science

This study aimed to evaluate the properties of soda lignin obtained from an unconventional and abundant waste - the rambutan peel - since lignin has been shown as the most promising natural organic feedstock alternative to petroleum for polymer science. FTIR analysis and pH measurements have confirmed the acidic form of lignin, which has shown solubility in a wide range of polarities and so many solvents, making its insertion easy on polymeric matrices. While the ability to absorb UV-light was higher than commercial lignin tested as reference, the morphology and size distribution at microscopic level were less regular than that. When added to a starch-based film, the lignin decreases its natural affinity for water, improving the barrier properties, as well as increasing its thermal resistance. Microorganisms could be developed easily on starch-based films containing this kind of lignin. This material, still underreported for technological applications, points towards as promisor to be a component or additive in polymeric matrices.

Cyclodextrins in Polymer-Based Active Food Packaging: A Fresh Look at Nontoxic, Biodegradable, and Sustainable Technology Trends

Using cyclodextrins (CDs) in packaging technologies helps volatile or bioactive molecules improve their solubility, to guarantee the homogeneous distribution of the complexed molecules, protecting them from volatilization, oxidation, and temperature fluctuations when they are associated with polymeric matrices. This technology is also suitable for the controlled release of active substances and allows the exploration of their association with biodegradable polymer targeting to reduce the negative environmental impacts of food packaging. Here, we present a fresh look at the current status of and future prospects regarding the different strategies used to associate cyclodextrins and their derivatives with polymeric matrices to fabricate sustainable and biodegradable active food packaging (AFP). Particular attention is paid to the materials and the fabrication technologies available to date. In addition, the use of cutting-edge strategies, including the trend of nanotechnologies in active food packaging, is emphasized. Furthermore, a critical view on the risks to human health and the associated updated legislation is provided. Some of the more representative patents and commercial products that currently use AFP are also listed. Finally, the current and future research challenges which must be addressed are discussed.

Production of PP Composites Reinforced with Flax and Hemp Woven Mesh Fabrics via Compression Molding

Hemp and flax fibers are among the most interesting vegetable fibers that can be used to reinforce polymeric matrices. In line with the global environmental requests, the use of these fibers especially coupled with thermoforming polymers are increasing more and more in order to expand their applications and replace synthetic fibers and thermosetting plastics. However, one of the major limitations of vegetable fibers is their poor adhesion with polymeric matrices that is often overcome by fibers chemical treatments or by using coupling agents within the matrix. Aiming to produce polypropylene (PP) bio composite laminates reinforced by hemp and flax fibers without additional process steps, this paper deals on the study of their production via the compression molding technique by using woven fabrics characterized by a large mesh size able to ensure a mechanical anchoring between fibers and matrix. Two different forming strategies that differ in the time required for reaching the maximum values of compression pressure and in the dwelling time at this value were used in order to investigate how the yarn impregnation was affected by them. To expand the applications of composites under investigation, tensile, bending, Izod, heat deflection temperature (HDT) and bearing tests were carried out. The results highlighted how the use of a waiting time before the reaching of the maximum moulding pressure allowed a better matrix flow within the vegetable yarn leading to higher mechanical performances.

Thermal behaviour of benzoxazine blends based on epoxy and cyanate ester

In the present work, an attempt has been made to develop high-performance polymeric hybrid binary blends of epoxy/benzoxazine and benzoxazine/cyanate ester with varying weight percentages (25/75, 50/50 and 75/25 wt%) of resins, namely, bisphenol-F epoxy resin (DGEBF), benzoxazines [bisphenol–F/aniline (BF-a) and imidazole core-based bisphenol/aniline (IBP-a)] and cyanate ester [bisphenol-F bifunctional cyanate ester (BF-CE)]. The molecular structure, polymerisation temperature/cure behaviour, glass transition temperature (Tg) and thermal stability of the neat polymeric matrices and binary hybrid blends of polymeric matrices were characterised using different analytical techniques, viz. Fourier Transform infra-red spectroscopy (FTIR), Nuclear Magnetic Resonance spectroscopy (NMR), Differential Scanning Calorimetry (DSC) and thermogravimetric analysis (TGA). Among the binary hybrid blends, the lowest polymerisation temperatures (Tp) were noticed in the case of blends of epoxy/benzoxazine were 219°C for DGEBF/BF-a (25/75 wt%) and 170°C for DGEBF/IBP-a (25/75 wt%). Similarly, in the case of blends of benzoxazine/cyanate ester, the lowest values of Tp observed were 155°C and 153°C for BF-a/BF-CE (75/25 wt%) and IBP-a/BF-CE (75/25 wt%), respectively. The highest values of Tg observed for the blends of epoxy/benzoxazine were 175°C and 254°C for DGEBF/BF-a (25/75 wt%) and DGEBF/IBP-a (25/75 wt%), respectively. Whereas, the highest values of Tg observed in the case of blends of benzoxazine/cyanate ester were 234°C and 278°C for BF-a/BF-CE (25/75 wt%) and IBP-a/BF-CE (75/25 wt%), respectively. From the TGA results of blends, the maximum degradation temperature (Tmax) and limiting oxygen index (LOI) value calculated from the char yield, which ascertain that almost all the binary hybrid blends of epoxy/benzoxazine and benzoxazine/cyanate ester possess good flame retardant behaviour.

UTILIZATION OF GRAPHENE OXIDE IN BUILDING MATERIALS

Cement-based materials (CBM) is one of the most commonly used building materials. Due to their brittle nature (sudden failure, low tensile strength, low resistant to crack), CBMs were modified through the addition of various traditional fillers/ reinforcement such as fibres and supplementary cementutious materials. Advanced modifiers/fillers such as Graphene-based nanomaterials (GBM) were utilized due to their superior properties in upgrading properties of CBM. GBM have been firstly used to enhance various polymeric matrices for storage energy, sensors and bio-applications. Following that, GBM were utilized in CBM with remarkable improvements in properties. In the current paper, an overview on the synthesis and structure of one type of GBM; namely graphene oxide (GO) was presented. The impact of GO on properties of CBM was addressed. One of the most observations from the highlighted published work was that the enhancements in CBM properties were linked to the uniform dispersion of functionalized GO and template effect of GO in CBM. Although GO with its attractive properties in upgrading properties of CBM, the usage of GO in construction industry is still not at the same demand level as in other applications and further investigations are needed in this regard.

CORRELATIVE AND COVARIANCE ANALYSIS OF THE ELECTROCONDUCTIVE FABRICS

This paper presents the correlation and covariance analysis of the electrical resistance dependence of mass, thickness and air permeability of textile structures coated with magneto-conductive materials and used for protection against electromagnetic waves. For this scientific approach, 9 experimental models of compositesbased fabrics with electroconductive properties were made by applying different pastes based on organic polymeric matrices polyvinyl alcohol (PVA), copper (Cu), aluminium (Al), zinc (Zn), iron oxide (Fe3O4) and polypyrrole (PPY) solution using a classical deposition method such as scraping. The surface resistance was evaluated using a resistance meter device based on two parallel electrodes. From all samples analysed 5 samples based PPY, PVA-Ni, PVA–Ni-Al and PVA-Zn present a surface resistance between 103 and 105 Ω. Because the surface resistance has a lower value this means that the samples have a good conductivity to be used as layers for electromagnetic shielding systems.

Stabilization Techniques of Essential Oils by Incorporation into Biodegradable Polymeric Materials for Food Packaging

Human health, food spoilage, and plastic waste, which are three great topical concerns, intersect in the field of food packaging. This has created a trend to replace synthetic food preservatives with natural ones, to produce bio-functional food packaging, and to shift towards biodegradable polymeric materials. Among the natural bioactive agents, essential oils are gaining more and more attention in food packaging applications due to their various benefits and fewer side-effects. However, their volatility, hydrophobicity, and strong odor and taste limit the direct use in food-related applications. Fixation into polymeric matrices represents a suitable strategy to promote the benefits and reduce the drawbacks. Emulsification and electrospinning are largely used techniques for protection and stabilization of essential oils. These methods offer various advantages in active food packaging, such as controlled release, ensuring long-term performance, decreased amounts of active agents that gain enhanced functionality through increased available surface area in contact with food, and versatility in packaging design. This review focuses on creating correlations between the use of essential oils as natural additives, stabilization methods, and biodegradable polymeric matrices or substrates in developing bioactive food packaging materials. Documentation was performed via the Scopus, ScienceDirect, and PubMed databases, selecting the publications after the year 2018. Particular attention was given to the publications that tested materials on food/food pathogens to evaluate their performances in retarding spoilage. Research gaps were also identified on the topic, materials being tested mainly at short time after preparation without considering the long-term storage that usually occurs in actual practice between production and use, and insufficient research related to upscaling.

FUNCTIONALIZATION OF THE SURFACE OF HYPERCROSSLINKED POLYSTYRENE FOR CATALYST SYNTHESIS

Нанесенные наноразмерные катализаторы широко используются в различных процессах химической технологии. При этом особые требования предъявляются к носителю, используемому при синтезе катализаторов. Сверхсшитые полимеры являются перспективными носителями, однако зачастую не имеют требуемых свойств (например, кислотности). Для придания дополнительных свойств возможно модифицировать поверхность полимеров различными веществами или функциональными группами. В данной работе проведено исследование способов модификации и веществ-предшественников кремнийсодержащей фазы для модификации поверхности сверхсшитого полистирола диоксидом кремния. The supported nano-scale catalysts are widely used in different fields of chemical engineering. For the catalysts, the certain requirements are specified fort the catalyst supports. Hypercrosslinked polymers seem to be the prospective materials for the catalyst synthesis. However, polymeric matrices often do not meet some standards for catalyst supports (i.e. polymers are inert materials and do not have the acidic or basic properties). To infuse the additional properties to polymers it is possible to modify its surface with different compounds or functional groups. In this work, the study of the ways for the modification of the surface of hypercrosslinked polystyrene and silica-phase precursors was carried out.