Gas-Laden Pellet Microcellular Injection Molding Foaming Technology Portfolio

Microcellular injection molding, also known as ‘microcellular foaming,’ is a process that produces lightweight and dimensionally stable plastic components while using fewer raw materials than standard injection molding techniques. However, conventional microcellular foaming techniques require specialized equipment and supercritical fluids, which increase the price of the technique. In addition, the surfaces of components fabricated using conventional techniques tend to be irregular or rough.

UW–Madison researchers have developed new methods of fabricating highly foamed, injection-molded plastic parts, including personal and consumer care products and packaging. The new techniques require much lower equipment cost and process complexity than conventional microcellular foaming methods. Additionally, no modifications to the injection molding machines are needed, all the same benefits that conventional methods offer can be achieved and the surface finish of the parts is improved.


Superior Plastic Parts

UW–Madison researchers have developed a new method to create foamed, injection-molded plastic blends with significantly increased toughness and ductility compared to conventional foamed parts.

The new process begins with a polymer blend with two properly selected polymer materials, such as polypropylene (PP) and high-density polyethylene (HDPE), or PP and low-density polyethylene (LDPE), which exhibit a dispersed secondary phase at sub-microscale in the primary matrix. The polymer blend is heated along with a supercritical fluid in an extruder to produce a melt, which is then extruded into gas-laden pellets. The gas-laden pellets can be fed into the injection barrel of a typical machine, plasticized and then injected into a mold cavity (or cavities) where the final part is made.

The process forms a lightweight component with microscale air cavities. Upon tensile loading, debonding of the secondary phase facilitates the interconnection of microcellular voids to form channels such that the stretched component becomes a bundle of fibrils. Compared to other toughening methods, this method achieves a more significant improvement in ductility and toughness. It also has the benefit of higher production efficiency, better dimensional stability, and greater design freedom thanks to the foamed injection molding process.

Highly Foamed Plastic Parts Are Stronger and Cheaper to Produce

UW–Madison researchers have developed a new method of fabricating highly foamed, injection-molded plastic parts. Firstly, a thermoplastic material like LDPE is heated along with supercritical nitrogen or carbon dioxide to produce a gas-polymer solution in an extruder, and then the melt is extruded and quenched into gas-laden pellets. These pellets are plasticized in an injection molding machine, and then injected into a mold to produce lightweight parts with fine foamed structure and/or improved part surface.

Compared with the conventional method, this method requires much lower equipment cost and process complexity, no modification to the injection molding machines is needed, and all the same benefits that the conventional method offers can be achieved.

Microcellular Foamed Plastics with Reduced Cost and Improved Surface Quality

UW–Madison researchers have developed a method for fabricating injection molded components with higher quality and lower cost than conventional techniques. The method uses a liquid such as water combined with a nucleating agent such as commonly used additives or fillers to generate bubbles. The liquid is added into a hopper of an injection molding machine and combined with the nucleating agent. The liquid turns into a vapor during injection, which forms bubbles within the injection molded components. The nucleating agent acts to reduce bubble size and increase bubble density, resulting in finer surface quality in the molded parts. The method allows production of foamed plastic parts with a comparable weight reduction and similar mechanical properties as conventional microcellular foaming techniques with improved surface finish and reduced cost.

Smoother Plastic Products Using Microcellular Injection Molding

UW–Madison researchers and others have improved the microcellular injection molding process to create smoother plastic parts.

In the new process, a polymer is heated, melted and mixed with a low amount of supercritical fluid (such as nitrogen). The resulting mixture is a single-phase solution. The polymer and/or the supercritical fluid may be adjusted to control the weight of the component or its surface properties. Once adjusted, the mixture is injected into a mold. Proper control of the supercritical fluid content in the polymer causes bubbles in the polymer to nucleate in a controlled fashion, which leads to products with a much smoother surface.
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