Reactive rotational molding process of PP/PA6 bilayer systems: experimental investigations

Abstract

Rotational molding is a shear-free and pressure-free process used to manufacture hollow plastic parts with relatively low investment [1]. With the rotational molding industry presently being dominated by powdered plastics, in particular polyethylene with limited properties, moulders are being forced to use other forms of plastic processing. Other resins currently used by the industry such as polycarbonate and nylon offer better properties, but at a cost.Reactive rotational molding (RRM) is an important way to overcome these problems, this process offers manufactures numerous benefits over the conventional powder process including shorter cycle times, lower processing temperatures and improved in material properties [2]. Additionally the use of RRM process allows the synthesis of engineering thermoplastic as polyamide 6 with a high molecular weight through anionic polymerization of caprolactam by the aid of chain initiators and catalyst. The advantage of the anionic polymerization of caprolactam have been put to use in reactive polymerization-molding process, namely Rotational molding has been regarded as a plastic molding method with great potential. The process offers virtually stress free products having no weld lines or material wastage, and utilizes relatively inexpensive molds. Yet its widespread growth is hindered due to long production cycle times, which are limited by the time required to heat up and cool down the mold and the product. This presentation is about the study of making multilayer PP/PA6 parts with the reactive rotational molding process. Different studies have already been made in the past about rotational molding or about reactive process of monolayer part. The aim of this work is to reduce cycle time by making a layer via anionic polymerization of caprolactam, and them to compare each process. This presentation is divided into two parts: the first part deals with rheological, dieclectric aland thermal analysis to investigate the effect of mixtures and the crystallization/polymerization effect; the second part deals with the processing of bilayer parts. Firstly, different mixtures of catalysts and activators were investigated by Rheology and thermal analysis in order to determine which mixture would be the most appropriate for the rotational molding process: 2 2 (2% of activator and 2% of catalyst), 3 3, 4 4 and 6 6. In the second step, different processing investigations have been done in order to study the influences of the parameters like oven time or cooling time. An experimental analysis of heat transfer in reactive rotational molding process was also lead. By using an instrumented mold associated with a radio transmission data acquisition system, we demonstrate that the rotational parts of the bilyar PP/PA6 (reactive way) can be obtained with optimised conditions in correlation with the results of rheology and dielectric measurements. Moreover, the results allows us that it is possible to make bilayer reactive part with the rotational molding process by using less energy in a shorter t...

Polyamide from lactams by reactive rotational molding via anionic ring-opening polymerization: Optimization of processing parameters

“…A lowest possible rotational speed should be employed to minimize bubble formation [2]. The material density was assumed to be 1100 kg/m 3 . The wall thickness of the part was 0.002 m and the mold's major (R 1 ) and minor radius (R 2 ): were 0.125 and 0.05 m. The maximum solid-body rotation viscosity for the stated range of conditions was obtained according to Equation (3) as [2]: (3) where $ SBR = viscosity at which solid-body rotation occurs (Equation (4) …”

“…anionic polymerization of caprolactam by the aid of chain initiators and catalysts [3]. It is well known that anionic polymerization of !-CL (APCL) occurs faster (i.e., over a few minutes) than classical hydrolytic polymerization, which takes about 12-24 h [4].…”

Rotational molding: A review of the models and materials

“…LPSs have a long history of application in RM; beginning with PVC plastisols since the early 1940s, followed later by caprolactams and PU in the 1950s and 1970s respectively [113,114]. Subsequent works investigated and attempted to resolve the problems inherent to these materials, such as uneven material distribution and part porosity [108,[115][116][117][118][119][120]. Throne and Gianchandani [120], identified four flow regimes for a reactive polyester resin: cascading, rimming, stable hydrocyst, and solid body rotation (SBR) (Figure 7).…”

“…Indeed initial viscosity and rate of viscosity change are the variables that most significantly affect final part quality. When square molds are used, LPSs having lower initial viscosity alongside rapidly increasing viscosity profiles tend to produce parts with the most number of defects [115,117,119]. This is because irregularities in wall thickness that arise from flow disturbances (corners) are more likely to freeze into the moldings during gelation.…”

Novel method for fabrication of PP/HDPE/PP trilayer microporous membrane with a highly orientated structure

“…Co‐extruding is the second method that widely used in manufacturing multilayer products such as bicomponent fiber, multilayer flat film, and sandwiched composites . Other methods such as inorganic particles coating, multilayer extrusion blowing, and reactive rotational molding were also mentioned in some publications . Two major problems are unavoidable in the process: the processing equipment is complicated and expensive; interface bonding strength of the products is poor.…”