This review summarizes the results of cold atmospheric pressure plasma technology application in polymers surface treatment. Attention is given to results of changes in the hydrophilic property of polymer surfaces by incorporation of polar functional groups when exposed to atmospheric pressure plasma, depending on the time of treatment, applied voltage, gas flow rate, and distance from the surface. We have successfully developed a plasma device that is able to generate cold atmospheric pressure argon plasma of low temperature (20 – 26) ° C downstream using a high-voltage power source which can be widely used in materials processing. Therefore, a cost-effective system of generating a plasma jet at atmospheric pressure with potential applications has been developed. Cold atmospheric pressure plasma jet (CAPPJ) has shown a lot of applications in recent years such as in materials processing, surface modification, and biomedical materials processing. CAPPJ has been generated by a high voltage (0-20 kV) and high frequency (20-30 kHz) power supply.<br/> The discharge has been characterized by optical and electrical methods. In order to characterize cold atmospheric pressure argon plasma jet, its electron density, electron temperature, rotational temperature, and vibration temperature have been determined using the power balance method, intensity ratio method, Stark broadening method, and Boltzmann plot method, respectively. The improvement in hydrophilicity of the cold plasma-treated polymer samples was characterized by contact angle measurements, surface free energy analysis, Fourier transform infrared (FTIR) spectroscopy, and scanning electron microscopy (SEM). Contact angle analysis showed that the discharge was effective in improving the wettability of polymers after the treatment. Furthermore, atmospheric plasma can be effectively used to remove surface contamination and to chemically modify different polymer surfaces. The chemical changes, especially oxidation and cross-linking, enhance the surface properties of the polymers.

Various naturally-based chemicals can be used directly as wood adhesives or are precursors for the synthesis of adhesive resins. Liquefaction and pyrolysis of wood yield various smaller chemicals derived from the different wood components, which then are used in the preparation of adhesives by replacing mainly phenol as raw material. The possible replacement of formaldehyde in aminoplastic and phenolic resins would solve the question of the subsequent formaldehyde emission.<br/> The multiple unsaturations of the triglycerides in vegetable oils enable polymerization for the direct synthesis of thermosets, as well as bases for polyfunctionalization and crosslinking.<br/> Natural polymers, such as poly(lactic acid)s (PLAs), natural rubber, or poly(hyhydroxyalkanoate)s (PHAs) are thermoplastics and can be used for various special applications in wood bonding, in case they can also be crosslinked. For other thermoplastic wood adhesives, such as PUR or PA, chemicals based on natural resources can at least replace a part or even all synthetic raw materials (monomers); these monomers derive from targeted decomposition of the wood material in biorefineries.<br/> Cellulose nanofibrils (CNFs) can be used as as sole adhesives or as components of adhesives. Hydrogen bonding has a key function in binder applications related to adhesion between cellulose nanoparticles and other materials. CNFs are able to establish strong bonding between wood particles/fibres through flexible and strong films by a simple drying process.<br/> Cashew nut shell liquid (CNSL) is a by-product of the cashew nut processing with cardanol (CD) as main component. CD-formaldehyde resins show improved flexibility compared to phenol-formaldehyde (PF) resins; CD can replace up to 40% of the phenol.

Recent progress in the adhesion mechanism of mussels has led to great excitement in the field of adhesive materials. Although great progress has been made in the mussel adhesion mechanism and underwater adhesives, there are still many unknowns and challenges in this area. Thus, it is highly important to review the recent progress in mechanisms of mussel adhesion and mussel-inspired adhesives and predict trends for the future. In this review, we (1) summarize the research progress in fundamental interaction mechanisms in natural mussels; (2) discuss the application of the mussel interaction mechanism in the biomimetic mussel adhesive materials, from permanent/high-strength adhesives to temporary/smart adhesives; (3) briefly state the potential applications of the mussel-inspired adhesives in multiple fields, such as engineering applications, smart robotics and biomedicine; (4) summarize the future perspectives and unsolved challenges of mussel adhesion mechanisms and mussel-inspired adhesive materials. We envision that this review will provide an insightful perspective in understanding the mussel adhesion mechanism and directions to further explore, and promote the development of novel biomimetic mussel adhesive materials.

This series of critical reviews on Wood Adhesives Based on Natural Resources (in total four parts) describes the experience and actual status of wood adhesives based on natural resources and gives an outlook into the future of these materials. Desite boundless results and papers in the development, purely naturally based wood adhesives are in industrial use only in negligible amounts; therefore this review series also reports on combinations of naturally based adhesives with synthetic components, such as modifiers or crosslinkers.<br/> Part I of this series concentrates on general topics and questions related to wood adhesives based on natural resources, such as systematic overview on the various types of naturally based wood adhesives, including cases where the adhesive is not applied separately but is used in situ, originating from the various components of the wood material. As a first product group, proteins from plants and animal sources and their use as wood adhesives will be described in this Part I.

This Part II of the series of critical reviews on Wood Adhesives Based on Natural Resources concentrates on the various carbohydrates and their decomposition products, which might be used as wood adhesives. This includes the use of native carbohydrates as such as adhesives, and also with chemical modification of carbohydrates by natural and synthetic components. Crosslinking in order to improve moisture and water resistance is achievable by natural and synthetic chemicals. Most promising options are realized by decomposition of various carbohydrates to small, well-defined monomers, which then can undergo various reactions, yielding again polymers in order to create a bondline. Suitable monomers are various furan moieties, such as 5-hydroxymethylfurfural. Activation of cellulose and hemicellulose at the wood or fibre surface by chemicals, such as citric acid, enables bonding effects without addition of an external adhesive. So far, however, carbohydrates are used only in very small amounts as industrially applied wood adhesives, despite tremendous R&D effort made and a huge number of scientific papers and reports published.

Due to the increasing discussion about sustainable and CO2-reduced materials, the demand for cellulose-based fibres as a reinforcing component in thermoplastic composites has increased considerably. Knowledge about the possibilities of modifying fibres for improved adhesion to the plastic matrix is essential in this context. The fibre/matrix adhesion in cellulose fibre-reinforced polymers is of considerable importance for the design of composite materials. Unfortunately, there are no standards for many essential methods to determine fibre/matrix adhesion. In this review article, various methods for measuring the interfacial shear strength between fibres and matrix, as an indirect characterisation of adhesion, are presented. Additionally, a brief overview of different methods for surface modification of cellulose fibres to improve the adhesion to a thermoplastic matrix is given. This review focuses on the fact that the parameters for the production of test specimens as well as the test method itself can vary considerably from study to study. Because of this, the comparison of data from different publications is not always possible. Therefore, in this article, the main influencing factors and differences in the methods are presented and discussed. Based on a systematic review and a clear description and discussion of the methods, the reader is given a broad basis for a better understanding of characteristic values for fibre/matrix adhesion.

The aim of this study is to present an efficient and effective technique to strategically investigate and classify the influence of a set of manipulated parameters that affect the mechanical properties and performance of adhesively bonded joints formed by an adhesive that is reinforced by various types of carbon nanoparticles (NPs). Specifically, single-lap joints (SLJs) are considered in this study. The selected parameters include the adherend types (i.e., carbon fiber-reinforced polymers (CFRPs) and glass fiber-reinforced polymers (GFRPs)), three types of nanoparticles (i.e., carbon nanofibers (CNFs), multi-walled carbon nanotubes (MWCNTs) and graphene nanoplatelets (GNPs)), different weight-percent (wt.%) of GNPs (i.e., 0, 0.5, 1%), and three different strain (or loading) rates, classified as static, quasi-static and impact loadings, herein. The study employed two mixed-level full factorial design of experiments (DOE) to evaluate the contribution of the aforementioned parameters, including the effect of their interactions on the enhancement of the averaged ultimate shear strength (AUSS) of the SLJs. The DOE study was conducted using the strength data (AUSS) obtained through testing of 108 SLJ specimens. The results indicate that among the considered parameters, NPs (wt%), adherend type, and strain rate had a greater effect on AUSS. According to the DOE conducted in this study, the greatest AUSS (19.9 MPa) could be obtained when 1.0 wt% GNP was used to reinforce the SLJs with CFRP adherend and subjected to the highest strain rate (HSR). This combination yielded a 32% enhanced AUSS compared to the SLJs formed by the neat adhesive.

Pellets are spherical shaped multiparticulate drug delivery systems with size ranging between 0.5-2.0 mm. Free flow, good mechanical properties, improved physical and chemical properties of powder, and stability are some advantages of pellets. Mucoadhesive pellets could be developed by using appropriate concentration and type of mucoadhesive polymer. Mucoadhesive pellets can be used for delivery of drugs to gastric, colonic, and vaginal regions. Immediate release, sustained/controlled release and implantable delivery could be incorporated using mucoadhesive pellets. Reproducibility, ease of scalability, quality control checks and significant mechanical strength are some advantages making pellets widely acceptable by pharmaceutical industry. In the present review, mucoadhesion process and theories, mucoadhesive polymers, pelletization process, evaluation of pellets and reported research/patents on mucoadhesive pellets for delivery of different categories of drugs have been presented.

The interfacial shear strength (IFSS) between natural sisal fiber and zein protein resin was explored using the microbond test. Commercially available zein protein was processed into resins and their IFSS with sisal fiber was measured. Effects of sorbitol plasticizer content and microfibrillated cellulose (MFC) reinforcement loading on the IFSS with the resin were studied. Scanning electron microscopy (SEM) was used to characterize the fracture surfaces before and after the microbond test. Energy dispersive X-ray spectroscopy (EDX) was utilized to map the residual resin on the sisal fiber surface after the microbond test. The results showed that sisal fiber/ zein IFSS decreased with sorbitol content. At 20 wt% sorbitol content 53% decrease in IFSS was observed. IFSS increased with MFC loading from 1.32 MPa (control) to 2.40 MPa for resin containing 15 wt% MFC. Physical entanglements between sisal fibers and MFC are believed to be responsible for this enhancement in the IFSS.

A critical review is provided to summarize our recent efforts to utilize the state-of-the-art bio-inspired icephobic coatings/surfaces, i.e., 1). Lotus-leaf-inspired superhydrophobic surfaces (SHS) and 2). Pitcher-plant-inspired slippery liquid-infused porous surfaces (SLIPS) for aircraft icing mitigation. By leveraging the unique Icing Research Tunnel of Iowa State University (i.e., ISU-IRT), an experimental campaign was performed to evaluate the effectiveness of using SHS and SLIPS coatings to suppress impact ice accretion over the surfaces of typical airfoil/wing models. While both SHS and SLIPS were found to be able to suppress ice accretion over the airframe surfaces where strong aerodynamic forces are exerted, ice was still found to accrete in the vicinity of the airfoil stagnation line where the aerodynamic forces are at their minimum. A novel hybrid anti-/de-icing strategy concept to combine icephobic coatings with minimized surface heating near airfoil leading edge was demonstrated to effectively remove impact ice accretion over entire airfoil/wing surfaces. An experimental investigation was also conducted to examine the durability of the icephobic coatings/surfaces to resist "rain erosion" effects (i.e., the damage to the surface coatings due to continuous impingement of water droplets at high speeds) in considering the practical usage for aircraft icing mitigation. The rain erosion effects were characterized based on the variations of the ice adhesion strengths and surface morphology of the eroded test surfaces coated with SHS and SLIPS. The research findings are very helpful to elucidate the underlying physics for the development of novel and robust anti-/de-icing strategies for aircraft icing mitigation.