Foaming nucleating agent

A wide variety of polymers can be foamed, including the polymethanes, polyisocyanurates, PVC, polystyrene, ABS, polycarbonate, PET, PBT, polyamides, PPO, EVA and the polyolefins. Other additives required for the foaming process besides blowing agents may include foam nucleating agents, stabilisers, surfactants, plasticisers, colourants, flame retardants and particulate fillers. 

Names Add-Vance BNX CAP CESA CN Foaming Nucleating Agent hmovex IP Klaritone MPM NAE NAM NC Palmarole Polyclear, PP Safoam WBG... 

ActiveX, Chemical foaming/nucleating agents, B.I. Chemicals, Inc., Specialty Products Div. 

EFFECT OF NUCLEATING AGENTS ON POLYPROPYLENE FOAM MORPHOLOGY... 

A material, such as (a) a terpolymer of propylene, ethylene and butene-1, (b) a polyolefin composition, which includes about 31 to 39% of a copolymer of propylene and ethylene and about 58 to 72% of a terpolymer of propylene, ethylene and butene-1 or (c) a polyolefin composition, which includes about 30 to 65% of a copolymer of propylene and butene-1 and about 35 to 70% of a copolymer of propylene and ethylene, is irradiated and extruded through a die in the presence of a physical expanding agent and a cell nucleating agent to produce a structure having a density, which is at least 10 times less than the initial density of the material. The foam articles exhibit improved flexibility and low temperature toughness compared to conventional propylene polymer materials. 

A study was made of nucleation in PE foams produced in a counter-rotating extruder using talc powders and masterbatches as nucleating agents and CFG and HCFC blowing agents. The results indicated the importance of shear force in nucleation, as proposed in the lump cavity nucleation model and demonstrated by melt temperature effects observed in these experiments. It was shown that shear enhancement via lump break-up was not a vital mechanism in nucleation. 6 refs. 

In search of easy dispersible nucleating agents with a high number of nucleants per volume, Spitael et al. [19] investigated the use of nanoscale diblock copolymer micelles on the batch-foaming behavior of PS. The diblock copolymers were composed of a PS block, and either PDMS, PEP, or PMMA as a second block. Several factors were identified as essential for nucleation, e.g., the size of the micelle and the surface tension of the micelle core material. 

Foaming of nanostructured blends - so far, only the use of low contents of block copolymers (up to 2 wt%) as nucleating agents was discussed [19]... 

For evaluating the efficiency of the nanostructured interface for cell nucleation, the particle density of PPE, as a measure for the number of nucleating sites available for nucleation, is plotted versus the nucleation density observed for the foam (Fig. 21). For comparison, the previously found values of the uncompatibilized PPE/SAN blend are added. For PPE/SAN, even the relatively high number of PPE particles of around 5 x 10ncm-3 only leads to nucleation of approximately 2.5 x 1010 cells cm-3, i.e., only 1/20 of the potentially available PPE particles act as cell nucleating agents. Via compatibilization, however, not only the particle density of PPE and the nucleation density can be increased, but also the efficiency is strongly enhanced. While the number of cells directly scales with particle density, more than two foam cells are nucleated by one PPE particle. 

Applications for these foamed products are many. An example is meat trays that are normally produced from PS foamed sheet with a thickness of approximately 0.095 in. and a density of about 5 lb/ft3. These trays are manufactured with little skin. The meat should not stick to the plastic when frozen, nor should the meat juice penetrate into the tray, and the tray should not break when handled. Strength is achieved by correcdy orienting the sheet resulting in cells that are round from a plan view. The cell size, which is determined by the amount and type of nucleating agent, is kept fairly fine to give the trays a soft, glossy appearance. 

---