Analyses of the Adhesion Interphase of Isotactic Polypropylene Using Hot-Melt Polyolefin Adhesives

Observation and Control of Single-Component Adhesion Interphase of Polyamide 66 through Confocal Raman Microspectroscopy

Manufacturing using adhesion technology has attracted much attention. Examples of adhesion include the lay-up of carbon fiber reinforced thermoplastic prepregs and the lamination of food packaging. In single-component adhesion systems, the analysis of the boundary region poses challenges because of the absence of chemical and physical discrimination at the adhesion interphase. Polyamide 66, one of the typical engineering plastics, is widely accepted as a structural material in automobiles and packaging films. Therefore, finer control of adhesion with polyamide 66 is crucial for advancing adhesion manufacturing. In this work, we focused and investigated the interphase of a single-component adhesion system with polyamide 66. For the analyses of single-component polyamide 66 laminates, an adhesion system with nondeuterated and deuterated polyamides was utilized, and their interphase structures were evaluated by confocal Raman microspectroscopy. The interphase region of the adhesion specimens was able to be characterized and evaluated, revealing an expansion to a thickness of several micrometers. The interphase thickness was increased with thermal annealing postlamination, whereas no thickness increase was observed in adhered specimens using the polyamide 66 substrates through thermal crystallization before lamination. The formation of the interphase region can be attributed to the crystal growing and lamella interlocking in the boundary region. Moreover, the larger interphase thickness was strongly associated with an increase in adhesion fracture toughness. These results suggested that the adhesion properties of crystalline substrates were decided by crystallization behavior and the thermal annealing process, even when using the same component adhesion systems.

Structural, electrical, and physical-mechanical properties of composites obtained based on filled polyolefins and thermoplastic elastomers

The paper presents the results of a study of the influence of various mineral and metal fillers, as well as carbon black and graphite on the structural features and quality of composite and nanocomposite materials based on polyolefins and their modifications. High density polyethylene (HDPE), low density polyethylene (LDPE), various copolymers of ethylene with α-olefins, polypropylene (PP), polypropylene random copolymer, block copolymer of ethylene with propylene, etc. were used as polyolefins. The filler used was mainly carbon black (CB) and graphite, as well as various natural minerals. The objective of the review material under consideration was to demonstrate promising possibilities for obtaining electrically conductive composite and nanocomposite materials based on dielectric polymers, which are included in the polyolefins. The introduction section examines the state of the problem of development and research of electrically conductive nanocomposites, as well as the goals and objectives of the research. The theoretical aspects of obtaining and studying composite materials based on polyolefins are considered, where the main attention is paid to studying the influence of filler content on the structural features and properties of polymer composites. Particular attention is paid to the compatibility of the mixture components and the establishment of the relationship between the filler particles and the macrochains of the polymer matrix. The significant role of compatibilizers in improving the compatibility of mixture components is shown. The article presents scientific provisions and theoretical background that explain the mechanism of the compatibilization process and its influence on the pattern of changes in electrical conductivity, physical, mechanical, thermophysical and thermal deformation properties of nanocomposites. Much attention is paid to the development of thermoplastic elastomers, taking into account the specifics of the interaction of thermoplastic (polyolefin) macrochains with various synthetic elastomers based on natural, butadiene-nitrile, butadiene-styrene and ethylene-propylene-diene rubbers. The influence of the thermoplastic-elastomer ratio, carbon black and graphite, and their modifications on the structure and properties of nanocomposites based on thermoplastic elastomers is considered. Significant attention is paid to the study of electrical conductivity of nanocomposites based on thermoplastic elastomers. It has been established that the degree of crystallinity of polyolefins and thermoplastic elastomers has a significant effect on the formation of the interspherulitic amorphous region in filled composites, which, in turn, has a primary effect on the mechanism of formation of tunnel and electron conductivity.

Electronic Interaction of Epoxy Resin with Copper at the Adhered Interface

A better understanding of the aggregation states of adhesive molecules in the interfacial region with an adherend is crucial for controlling the adhesion strength and is of great inherent academic interest. The adhesion mechanism has been described through four theories: adsorption, mechanical, diffusion, and electronic. While interfacial characterization techniques have been developed to validate the aforementioned theories, that related to the electronic theory has not yet been thoroughly studied. We here directly detected the electronic interaction between a commonly used thermosetting adhesive, cured epoxy of diglycidyl ether of bisphenol A (DGEBA) and 4,4'-diaminodiphenylmethane (DDM), and copper (Cu). This study used a combination of density functional theory (DFT) calculations and femtosecond transient absorption spectroscopic (TAS) measurements as this epoxy adhesive-Cu pairing is extensively used in electronic device packaging. The DFT calculations predicted that π electrons in a DDM molecule adsorbed onto the Cu surface flowed out onto the Cu surface, resulting in a positive charge on the DDM. TAS measurements for the Cu/epoxy multilayer film, a model sample containing many metal/adhesive interfaces, revealed that the electronic states of excited DDM moieties at the Cu interface were different from those in the bulk region. These results were in good accordance with the prediction by DFT calculations. Thus, it can be concluded that TAS is applicable to characterize the electronic interaction of adhesives with metal adherends in a nondestructive manner.

Surface Treatments of PEEK for Osseointegration to Bone

Polymers, in general, and Poly (Ether-Ether-Ketone) (PEEK) have emerged as potential alternatives to conventional osseous implant biomaterials. Due to its distinct advantages over metallic implants, PEEK has been gaining increasing attention as a prime candidate for orthopaedic and dental implants. However, PEEK has a highly hydrophobic and bioinert surface that attenuates the differentiation and proliferation of osteoblasts and leads to implant failure. Several improvements have been made to the osseointegration potential of PEEK, which can be classified into three main categories: (1) surface functionalization with bioactive agents by physical or chemical means; (2) incorporation of bioactive materials either as surface coatings or as composites; and (3) construction of three-dimensionally porous structures on its surfaces. The physical treatments, such as plasma treatments of various elements, accelerated neutron beams, or conventional techniques like sandblasting and laser or ultraviolet radiation, change the micro-geometry of the implant surface. The chemical treatments change the surface composition of PEEK and should be titrated at the time of exposure. The implant surface can be incorporated with a bioactive material that should be selected following the desired use, loading condition, and antimicrobial load around the implant. For optimal results, a combination of the methods above is utilized to compensate for the limitations of individual methods. This review summarizes these methods and their combinations for optimizing the surface of PEEK for utilization as an implanted biomaterial.