فصلنامه بسپارش
سال سیزدهم شماره 2 (پیاپی 47، تابستان 1402)

Polyethylene is one of the most widely used polymers in the food packaging industry. Due to high structural diversity, low cost, easy processability, and flexibility in the design and architecture of chains and their impact on the control of polymer engineering properties, different grades of polyethylene have made them one of the most important options in the manufacture of polymer food packaging. The outdoor high consumption of polyethylene has caused the process of stabilizing it against UV radiation as the main factor of degradation in the outdoor to increase its usage time. This indicates the need to increase the stability of this polymer against photodegradation. Generally, there are three ways to improve the stability of polymers against photodegradation: blocking or preventing the radiation from coming into contact with the polymer (mainly ultraviolet), using wave absorbing additives, and using additives that deactivate photodegradation reactions or the intermediate materials in the polymer. In the past decades, many advances have been made in the use of steric hindered amine compounds and their derivatives to increase the photostabilization of polymers. These compounds were generally introduced in four different categories to improve the optical stability performance of polymers by various mechanisms such as reducing and eliminating hydroperoxides, intermediate ions, quenching the excited state, and preventing the occurrence of photoreactions of polymers against UV radiation. In the following, after introducing these materials and their effectiveness mechanisms, various methods to improve the compatibility of amine stabilizers with polyethylene matrix were reviewed.

The regeneration process is not only affected by interactions between cells but also the surfaces chemistry of biomaterials. For this reason, modifying the surface of electrospun fibers with biomolecules is a suitable method to increase adhesion and cellular organization. There are two general approaches to modify electrospun nanofibers, which are performed in different ways. Loading biological agents in a polymer solution is a common method for trapping biomolecules in the scaffold structure, in which the molecule is located in the fibrous labyrinth and plays its role. However, due to the limitations of this method, post-modification methods have been considered as an alternative path. This type of modification can be achieved by physical adsorption of biomolecules on the fiber surface or by chemical bonding. Due to the capabilities of click chemistry, clickable electrospun structures provide a promising path for linking different biomolecules, that are suitable for different purposes of tissue engineering. In this article, the latest research performed on the functionalization and modification of electrospun structures with different types of click reactions are reviewed. Obviously, achieving smart systems that stimulate and control the cellular activities requires familiarity with the latest research in this field, which is the main goal of this review article.

In recent years, dendrimers as a new class of polymeric materials have attracted lots of attention due to their unique properties, especially as drug delivery systems. In this process, dendrimers can deliver medicine directly to the affected part of the patient's body. Dendrimers can be defined as macromolecular structures with several advantages, which may undergo changes depending on the chemical nature of the drug to be delivered. Dendrimers can be defined as macromolecular structures with several advantages that depending on the chemical nature of the drug to be delivered, they may change. The reason for the high attention paid to dendrimers in drug delivery is that they have properties such as uniform size, water solubility, modifiable surface performance, high degree of branching, being multivalent, well-defined molecular weight, and available internal cavities. In addition, the high level of control over dendritic architecture distinguishes them as ideal carriers. Also, the use of dendrimers in biomedicine has attracted the attention of many scientists. Biomedicine is one of the main fields of study of dendrimers due to their capacity to improve solubility, uptake, bioavailability and targeted distribution, and their value in diagnosis and treatment. In the last decade, anti-neoplastic research on dendrimers has been widely developed and several types of poly amidoamine (PAMAM) and poly propylene imine (PPI) dendrimer complexes with doxorubicin, paclitaxel, cisplatin, melphalan, and methotrexate have been improved compared to the drug molecule alone.

Lighter than air systems (LTAs) are the new air navigation system that usually float 20 km above the ground. It has been known that remote radio bases are defined at an altitude of 20 to 50 km above the ground, therefore, LTA systems have been considered as satellite communication networks. Today, the airship is contemplated one of the lighter than air systems as a carrier for humans and goods with low cost and maximum efficiency. The body of this system is composed of polymer multilayer structures including fibers, fabrics, and various film layers with a light gas (exp. H2 and He) retention characteristic, high tensile modulus, high resistance to internal and external pressure, and tolerance to high-temperature changes. In order to connect the layers and their sealing strength, polymer adhesives with low-temperature tolerance, high tensile strength, and high flexibility are used. Despite the many studies on these systems, there are still many opportunities to study the LTA industry. Therefore, in the present article, an attempt has been made to take an effective step in searching these systems and their types and identifying the components through the introduction of airships. Also, information about adhesives as bonding materials for body structures and finally the properties of polyurethane adhesives specific to these systems as the main adhesives of LTA systems are reviewed.

light-based three dimensional (3D) printing processes which are based on the use of light-sensitive monomers or oligomers, are the most versatile and interesting technique due to the unique potential to design structures with complex geometry, the ease of the process, the availability of the required compounds as well as the feasibility of tailoring materials to achieve the required properties. In this approach, photoinitiators are considered the key elements in the success of this process, and several types of research have been performed to introduce initiators with enhanced efficiencies. This article reviews the types of photoinitiators used in 3D printing technology and highlights the research carried out to transfer the absorption region of the compounds from the ultraviolet region to the visible region. In addition, water-soluble photoinitiators are also of great interest for use in the bioprinting of hydrogel systems, which are reviewed in this article. Obviously, success in the development of the 3D printing process and fabrication of constructs with suitable mechanical properties as well as resolution requires familiarity with the key elements involved in the process, therefore, one of the most important factors is investigated

In recent years, thin and ultrathin polymer films coated on solid surfaces have been widely used in various industries such as coatings, adhesives, membranes, sensors, etc. However, as the film becomes thinner, the effect of the interfaces increases, so that in thicknesses below 100 nm, the structure and properties of such ultrathin films, including surface properties such as surface free energy, undergo significant changes relative to the bulk of the same polymer. Considering the importance of surface free energy as a controlling factor in many industrial and theoretical phenomena such as adsorption, wettability, lubrication, etc. in polymers, this article aims to review the changes in surface free energy of ultrathin polymer films with changing their thicknesses. Two main factors have been identified in the literatures for surface free energy changes with changing films thicknesses in ultrathin polymer films. First, the long-range forces acting on the chains from the substrate as well as on the droplet placed on the film surface in order to measure the contact angle, and second, the finite size effect that in thicknesses comparable to the gyration radius of polymer chains, along with the intra- and intermolecular entanglements, can strongly affect the conformation of polymer segments as well as the chain mobility in ultrathin films which are slightly screening out with increasing the film thickness.