Effect of process parameters on the adhesion strength in two‐component injection molding of thermoset rubbers and thermoplastics

Recently, a novel two‐component injection molding process has been developed for combining thermoplastics with thermoset rubbers. This process is of interest for example when thermoplastic parts include seals which are usually produced out of thermoset rubber. The present study evaluates the influence of different process parameters on the bond strength by means of a half factorial experimental design. The considered process parameters are the mold temperature at the interface, the injection temperature, the injection speed, the holding pressure, and the initial roughness of the thermoplastic part at the later interface. The study indicates a large influence of the mold temperature at the interface. Furthermore, the holding pressure only affects the adhesion strength when it is set too low or when the holding time is too short. The other process parameters have no significant effect on the adhesion strength. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46495.     

Adhesion between ethylene-propylene-diene monomer and thermoplastics in two-component injection molding: Effect of dicumylperoxide as curing agent

Strong adhesion at the interface is an important aspect in two-component (2K) injection molding. It was therefore investigated whether dicumylperoxide (DCP) as curing agent in ethylene-propylene-diene monomer (EPDM) could stimulate interdiffusion and/or induce chemical bonding with thermoplastics. EPDM mixtures containing DCP concentrations between 2 to 8 parts per hundred rubber (phr) were combined with polar and non-polar thermoplastics. Changes in EPDM physico-mechanical bulk properties were analyzed, and the adhesion was evaluated by high temperature contact angle measurements and tensile testing. Results showed that DCP concentration did not influence EPDM-thermoplastic compatibility. However, EPDM adhesion with polyethylene (PE) did improve when using up to 6 phr DCP (57% adhesion) as crosslinking is promoted. While with polypropylene (PP), adhesion linearly decreased (from 55% to 35% adhesion) with higher DCP concentrations due to prevailing scission reactions. Adhesion through chemical bonding with acrylonitrile-butadiene-styrene (ABS) caused better adhesion at 4 phr (43% adhesion) compared to polycarbonate (PC) at 4 phr (13% adhesion) where only limited interdiffusion occurs. Thus, selecting the optimal DCP concentration is highly important to boost adhesion between EPDM and thermoplastics. Furthermore, at these optimal DCP concentrations, physico-mechanical properties require consideration as these properties were significantly affected.     

Wetting measurements as a tool to predict the thermoplastic/thermoset rubber compatibility in two‐component injection molding

Recently a novel two‐component injection molding process has been developed combining thermoplastics with thermoset rubbers. Since the adhesion strength between the two materials strongly depends on the combination of a specific thermoplastic and a thermoset rubber, there is a need to predict their compatibility, defined as the formation of a strong interface. In this study, the wetting behavior of molten thermoplastics on rubber substrates is used to predict their compatibility since wetting is an essential step in the formation of a strong interface. Contact angle measurements at high temperatures showed that the wetting of polypropylene and polyethylene is the best in combination with ethylene propylene diene monomer rubber while nitrile rubber is best wetted by polycarbonate. The subsequent two‐component injection molding tests confirm that it is possible to combine these materials. Material combinations with a poor wetting behavior on the other hand are not suitable for two‐component injection molding. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46046.     

Effect of co-agents on adhesion between peroxide cured ethylene–propylene–diene monomer and thermoplastics in two-component injection molding

Two-component (2K) injection-molded products combining ethylene–propylene–diene monomer (EPDM) with polar or nonpolar thermoplastics require strong interfacial bonding. To optimize the adhesion, co-agents trimethylolpropane trimethacrylate (TMPT) and triallyl cyanurate (TAC) are compared and concentrations were varied between 0 and 12 parts per hundred rubber (phr). Changes in material compatibility were characterized by contact angle measurements at high temperature, the adhesion was evaluated by tensile testing, and physicomechanical properties of the EPDM bulk were analyzed. Results show that with polypropylene, the adhesion increases to an optimum (3 phr TAC or 6 phr TMPT) independent of the co-agent type, while for polyethylene only TAC (1.5 phr) effectively boosts adhesion. It is surmised that these optimal concentrations promote crosslinking reactions at the interface. For polycarbonate and acrylonitrile–butadiene–styrene, increasing TAC concentration causes higher adhesion due to improved compatibility. Furthermore, physicomechanical bulk properties change significantly with co-agent concentrations, making the optimal curing composition application dependent. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48414.     

Prediction of interfacial strength of HDPE overmolded with EPDM

Multicomponent injection molding often combines a stiff thermoplastic material with a thermoplastic elastomer or thermoplastic vulcanite. Recently, for high‐demanding applications, a novel process has been developed to replace these thermoplastic elastomers or vulcanite with a thermoset rubber, for example, NBR or EPDM. One of the most important properties of a two component product is an adequate adhesion between both components. This paper describes a method, which combines experiments and numerical simulations to predict the adhesion strength between a thermoplastic, semicrystalline HDPE, and an EPDM thermoset rubber. This method uses numerical simulations of the interfacial temperature and the local degree of cure. The local interface temperature is combined with the results of DSC measurements to predict the degree of melting, subsequently linked to the ability to develop adhesive strength. The degree of cure is used to determine the local rubber strength. The combination of the given data will be used to predict interfacial strength. The results obtained by proposed numerical strategy have been successfully validated with experimental data on a simple plate product. POLYM. ENG. SCI., 59:1489–1498 2019. © 2019 Society of Plastics Engineers     

Study of the bending modes in circular quartz resonators

An experimental and theoretical study of bending modes in a partially electroded circular piezoelectric quartz (AT-cut) with free edge is presented. The quartz is excited by a voltage pulse applied on the electrodes, and its surface is scanned by a laser vibrometer that measures the out-of-plane displacements. The classical theory of bending of thin disks is used to describe the flexural modes at frequencies lower than the first thickness shear resonance (6 MHz). A fairly good agreement is found between experimental and theoretical results for the forced mode shapes and for the resonance frequencies. However, it appears that the two springs used to maintain the disk in position introduce extra clamping conditions. Several source shapes were studied, among which a collection of an arbitrary number of forces is particularly useful. The two-dimensional wavenumber representation shows the presence of anisotropy related to the crystallographic axes at higher frequencies, which is not predicted by the model. The experimental phase velocities are compared to those given by the classical theory of disks and to those of Lamb A(0) mode. This study confirms the correspondence at low frequencies between the A(0) mode and the bending eigenmodes of a disk with finite size.     

Dye Modification of Nanofibrous Silicon Oxide Membranes for Colorimetric HCl and NH3 Sensing

Colorimetric sensors for monitoring and visual reporting of acidic environments both in water and air are highly valuable in various fields, such as safety and technical textiles. Until now sol‐gel‐based colorimetric sensors are usually nonflexible bulk glass or thin‐film sensors. Large‐area, flexible sensors usable in strong acidic environments are not available. Therefore, in this study organically modified silicon oxide nanofibrous membranes are produced by combining electrospinning and sol‐gel technology. Two pH‐indicator dyes are immobilized in the nanofibrous membranes: methyl yellow via doping, methyl red via both doping, and covalent bonding. This resulted in sensor materials with a fast response time and high sensitivity for pH‐change in water. The covalent bond between dye and the sol‐gel network showed to be essential to obtain a reusable pH‐sensor in aqueous environment. Also a high sensitivity is obtained for sensing of HCl and NH₃ vapors, including a memory function allowing visual read‐out up to 20 min after exposure. These fast and reversible, large‐area flexible nanofibrous colorimetric sensors are highly interesting for use in multiple applications such as protective clothing and equipment. Moreover, the sensitivity to biogenic amines is demonstrated, offering potential for control and monitoring of food quality.     

Effect of loading a plate with different liquids on the propagation of lamb-like waves studied by laser ultrasonics

Three experimental laser ultrasonic configurations--line excitation with scanning detection, grating excitation with single point detection, and grating excitation with scanning probe beam--are shown to consistently reveal the modified propagation properties of Lamb waves on a polyethylene terephthalate (PET) film that is in contact with different liquids on its two sides. Theoretical predictions concerning the physical nature of different wave modes in symmetric and asymmetric film loading configurations (i.e., their existence, velocity, damping, and polarization) are confirmed by the experimental results.