Chemical Foaming Process Research Articles

Fabrication of Micro-Polymer Lenses With Spacers Using Low-Cost Wafer-Level Glass-Silicon Molds

A novel low-cost molding process to prepare polymer-based micro-lens arrays with spacers for optical applications was investigated in this paper. The process consists of the following steps: 1) hemispherical glass bubble arrays, used as the upper part of the molds, was prepared by combining a hot-forming process and a chemical-foaming process; 2) the silicon mold, used as the lower part of the molds, was fabricated by etching; 3) an anti-stick layer was coated on the concave surface of the glass mold; and 4) the lens material, UV-curable glue, was dispensed into the concave molds, followed by curing and de-molding. The optical properties of the lens were characterized by a profile meter and a beam analyzer. The results showed that the micro-polymer lens arrays with spacers were successfully prepared using the low-cost wafer-level glass-silicon mold. The results indicate that the micro-lenses have hemispherical structures and smooth surface.

Preparation of a Wafer-level Micro Polymer Lens Array With Improved Performance Using a Low Cost Glass Mold

In our work, polymer-based micro lens arrays with spacers were innovativly fabricated by low cost wafer-level glass-silicon molds. The upper glass mold was prepared by a well-controlled hot forming process (HFP) combined with a chemical foaming process (CFP). The under silicon mold was formed by an etching process. Before dispensing UV-curable glue between the two concave molds, the contact surface should be coated with an anti-stick layer. After UV curing and de-molding, the micro lens arrays were successfully fabricated. The lenses were inspected by an atomic force microscope(AFM), a white light interferometer and a beam analyzer. The results demonstrate the excellent quality of surface roughness and optical characteristics. This study indicates the potential of this novel molding process for industrial production.

Manufacture of lignocellulosic fiber–cement boards containing foaming agent

Combination of chemical foaming and air curing process is an alternative to produce fiber–cement boards out of Equisetum (Eq. telmateia) fibers and cement which would have low thermal conductivity and acceptable mechanical and physical properties. This study was conducted to determine the suitability of Equisetum fibers, silica fume gel (SFG) and micro aluminium powder as foaming agent (AL) to manufacture structural composite boards with target density and thickness of 1.10g/cm3 and 13mm, respectively. In these experimental boards macropores were created by adding AL as a chemical foaming agent; moreover, amount of cement in mixture has been optimized by specific amounts of SFG and Equisetum fibers. All boards were tested for their thermal conductivity, physical and mechanical properties according to specification JIS standards, and influences of additives on properties of produced fiber–cement boards were investigated as well. Results have revealed that mechanical properties of fiber–cement boards were improved by increasing Equisetum fibers and SFG contents whereas thermal conductivity did decrease. By increasing AL, both mechanical strengths and thermal conductivity were decreased. With regard to the physical properties, AL has led to increase in water absorption; however, SFG has deceased mentioned property. In general, comparison of these experimental boards with commercial composite boards in terms of measured properties confirms these composite boards as low thermal conductivity materials which are extremely desired for energy saving be used as ceiling and wall constructing material. In addition, physical and mechanical properties of such composites meet international standards.

Combined Effects of Chemical and Microcellular Foaming on Foaming Characteristics of PLA (Poly Lactic Acid) in Injection Molding Process

Foaming technology used in the plastic production process makes it possible to reduce costs and lighten the products, which is why this technology is widely used. Foaming technology is generally categorized as involving either a “Chemical Foaming Process” or a “Physical Foaming Process,” the latter also referred to as a “Microcellular Foaming Process” (MCP). In both processes, gas particles dissolved inside a polymer create cells. For the chemical foaming process, chemical blowing agents are mixed with plastic pellets, whereas for MCPs, gas is directly supplied to a polymer melted inside the barrel of an injection molding machine. The cell morphology changes when either the chemical foaming process or the MCP is applied in an injection foaming process. This study aims to compare and analyze the change of the cell morphology in such a case. In particular, Poly Lactic Acid (PLA) is used in the experiment. In this study, the foaming characteristics of a biodegradable material (PLA) and a convectional material – Acrylonitrile Butadiene Styrene (ABS) – are compared and analyzed. The analysis of the experiment results is done based on an analysis of the foaming ratio and a comparison of the cross-section of the cell morphology of specimens under different experimental conditions. For the former, a weight comparison was made, while for the latter, a scanning electron microscope (SEM) was utilized.

Rheometric study of the gelation and fusion processes of poly(vinyl chloride‐co‐vinyl acetate) plastisols with different commercial plasticizers

AbstractEvolution of the complex viscosity of pastes of PVC‐VA (vinyl chloride‐vinyl acetate copolymer) plasticized with different commercial plasticizers has been studied. Knowledge of the rheological behavior of the formulations allows for better understanding of the gelation and fusion processes. Twenty commercial plasticizers of different types and with different functional groups have been studied and are grouped into five families: phthalate esters with linear chains, phthalate esters with branched chains, adipates (normal and polymeric), citrates, and rest of the plasticizers (carboxylates, alkylsulfonates, and pentaerythritol ester derivatives). Interesting relationships among the observed rheologies and the nature and molecular weight of the plasticizer have been observed. The evolution of the complex viscosity with temperature—at the temperatures where the blowing agents normally used in PVC plastisol foaming processes generate the main amount of gas—has been newly discussed with regard to the chemical structure and molecular weight of all of the plasticizers used. It was found that several different dynamic processes must be synchronized in order to understand the relationships among the chemical structure, plasticization, plasticizer compatibility, rheological properties, and foaming process of such materials. J. VINYL ADDIT. TECHNOL., 2012. © 2012 Society of Plastics Engineers

Preparation of wafer-level glass cavities by a low-cost chemical foaming process (CFP)

A novel foaming process-chemical foaming process (CFP)-using foaming agents to fabricate wafer-level micro glass cavities including channels and bubbles was investigated. The process consists of the following steps sequentially: (1) shallow cavities were fabricated by a wet etching on a silicon wafer; (2) powders of a proper foaming agent were placed in a silicon cavity, named 'mother cavity', on the etched silicon surface; (3) the silicon cavities were sealed with a glass wafer by anodic bonding; (4) the bonded wafers were heated to above the softening point of the glass, and baked for several minutes, when the gas released by the decomposition of the foaming agent in the 'mother cavity' went into the other sealed interconnected silicon cavities to foam the softened glass into cylindrical channels named 'daughter channels', or spherical bubbles named 'son bubbles'. Results showed that wafer-level micro glass cavities with smooth wall surfaces were achieved successfully without contamination by the CFP. A model for the CFP was proposed to predict the final shape of the glass cavity. Experimental results corresponded with model predictions. The CFP provides a low-cost avenue to preparation of micro glass cavities of high quality for applications such as micro-reactors, micro total analysis systems (μTAS), analytical and bio-analytical applications, and MEMS packaging.

Characterization of highly filled magnesium hydroxide-polypropylene composite foams

Magnesium hydroxide—filled polypropylene foams were prepared by a compression-molding chemical foaming process and studied considering the effects of foaming and the presence of the particles on the microstructure (cellular structure and induced particle and polymer orientations), dynamic mechanical, and flame retardancy of the polypropylene composites. Two magnesium hydroxide concentrations, 50 and 70 wt%, as well as different foam densities, were considered. Results are discussed in terms of the observed anisotropy-induced cellular and particle and crystal orientations and their effects on the direction-dependent dynamic mechanical and flame behavior results. Preliminary flame retardancy characterization of the several solid and foamed composites showed interesting results due to foaming, foams globally exhibiting a higher extinguishability than the respective solid composites.

Plastisol foams – rheological and rheo-optical approach to developing new grades of poly(vinyl chloride)

In the chemical foaming process of poly(vinyl chloride) plastisols, gelation is one of the major parameters to be controlled in order to monitor the cell morphology of the foam. The expansion of the foam is governed by the rheological properties of the plastisol when the decomposition of the blowing agent occurs. The present paper shows the relevance of the viscoelastic properties to monitoring foam structure. The results demonstrate how such an approach can be used to develop new resin grades for a given formulation.