Blow molding moisture

A surprisingly low concentration of water can reduce the viscosity such that reclaimed PET cannot be used for the blow molding of bottles with acceptable physical properties. The established solution to the moisture problem is to dry the recycled PET in special dryers prior to use. However, the drying process is both time and energy intensive. Paper labels can cause problems in PET recycling if they decompose during washing and removal. The paper fibers formed can produce cellulose fibers that are difficult to remove from the reprocessed PET.1... 

EVOH have superior gas barrier properties.80 89 They are often used as the internal layer in multilayer food packaging films, blow molded rigid containers, gasoline tanks for automobiles for a variety of purposes, etc. EVOH can be fabricated by the usual melt processing methods. The barrier properties of films decrease in the presence of moisture, so multilayer with protective polypropylene (especially biaxially oriented material), low-density polyethylene, nylons, or other moisture barrier films provides films or products that are useful even with liquids. The... 

PET plastics are hygroscopic so require proper drying before processing. They can be extruded, blow molded, and thermoformed on conventional equipment if dried to a moisture content of less than 50 ppm. Recycling all types of PET materials is easily accomplished. Of the 2002 total USA 49.4 million units of PET beverage container market 57% contain carbonated soft drinks and 24% contain water.485... 

The second large group of styrenic blends comprises these with polyolefins — they are summarized in Tables 1.11 and 1.12. These blends are mainly used in packaging. Formulated for extrusion, injection and blow molding, they show excellent processability, improved impact strength, low moisture absorption and shrinkage. 

The harder grades of PP/EPDM blends (Santo-prene ) can be blow molded. The resins are characterized by a co-continuous morphology and high viscosity. The recommended parameters for blow molding are similar to profile extrusion. Moisture content is critical and should be kept below 0.1%. 

Blends of engineering resins used in blow molding applications include systems based on PA, PC and PPE. When using impact modified PA-6, PA-66 or PA-6,12 Zytel ), the moisture content must be signihcantly lower (0.05%) than that required for injection molding (0.25%). 

PC can be processed by injection molding, extrusion, coextrusion, and blow molding. Coextrusions with EVOH or polyamides are carried out with the help of adhesives. PC can be laminated or coextruded to PP, PE, PET, PVC, and PVDC. PC is a hydrophilic polymer, and at ambient conditions can reach moisture levels of 0.35%. 

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