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TECHNOLOGY | FOAMS


Right: SEM images of conventional PP processed with 0.6mL/min CO2


at 130 bar


die pressure (top image) and modified with 1% Dymalink 9200 under the same conditions


ers used (separately) nucleators from Polyfil (Ecocell P20) and Reedy Chemical Foam (Safoam FPE-20) at different loadings. Gallagher concluded that bio-based LDPE can be substituted for standard fossil-based LDPE for foaming applications, with no change in process conditions being required and similar foam properties being achieved. Whatever the source of the ethylene, an increase in foam nucleator reduces cell size, with excessive nucleation resulting in a higher open-cell count. However, the group found no clear correlation between cell size and tensile or tear strength.


Bio-based innovations At the AMI conference in the US last year, however, Braskem put the emphasis on foaming with polyeth- ylene. Thomas Gallagher, Technical Service Scientist with Braskem America, described investigations into the foam performance of bio-based polyethylene, which Braskem produces in Brazil using sugar cane as the source of the ethylene and which has a much lower carbon footprint than fossil-based PE. Gallagher and his colleagues compared the performance of various extruded foams produced from a bio-LDPE, I’m Green SLD4004, with a fossil-based LDPE also made by Braskem, Idesa LDF2023. The two polymers have similar properties (identical MFIs of 2.1 g/10 min at 190°C, 2.16kg; respective densities of 0.918 and 0.921 g/cm3


;


comparable rheological behaviour). The foams were physically blown with CO2


, and the research-


Foaming applications At Ecocell producer Polyfil, Renee Lapierre, Technology Manager Foams, says the company’s patented foaming agent technology is finding itself in new applications. “Ecocell has been evaluated by several of the major resin producers for use in PP both as a nucleator and as a blowing agent,” she says. “As a nucleator for HMS polypropylene, users report smallest cell size, less tendency to over- nucleation and the least number of open cells when compared to traditional endothermic CFAs containing sodium bicarbonate.” New Ecocell grades are also being used as the principal blowing agents to produce foamed PP, PET and HIPS sheet destined for thermoforming, Lapierre reports. “A microcellular structure, less open cell, no blow-outs and an ease of thermo- forming are reported by users,” she says. “Ecocell has been approved and enjoying commercial success in all mentioned cases.” Chemische Fabrik Budenheim’s Budit F Series endothermic foaming agents were discussed by Theresa Wassmer, Business Development Manager, Polymers, at the AMI Hamburg conference. As with other such additives, these are designed for chemical foaming processes to improve the melt flow, control cell formation, and eliminate sink marks in finished parts. Wassmer pointed out that Budit F additives “are eco-friendly due to non-hazardous


Table 3: Comparison of properties of sheet foamed from Braskem’s I’m Green SLD4004 and Idesa LDF2023 (US units; tests carried out to ASTM D3575) Parameter Nucleator


SLD4004 Ecocell P20 Nucleator loadng


Compression Strength @ 25% (psi) Compression Set (%) Tensile Strength (psi) Tear Resistance (lbs/in) Source: Braskem


58 COMPOUNDING WORLD | January 2019


0.2% 21 9


171 52


0.6% 22 5


203 60


Safoam FPE-20 0.2% 26 7


190 63


0.6% 25 7


161 58


0.2% 29 7


172 69


LDF2023 Ecocell P20


0.6% 22 5


186 55


Safoam FPE-20 0.2% 33 11


0.6% 33 11


180 62


213 63


www.compoundingworld.com


PHOTOS: TOTAL CRAY VALLEY


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