TECHNICAL INFO

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1 ArmaFORM AC grade PET core mechanical properties vs temperature Introduction ArmaFORM AC grade PET core material exhibits a glass transition temperature (Tg) close to 75 C, normally foam cores cannot be used at much higher temperatures than their Tg However crystallization in ArmaFORM PET cores produces a crystalline structure that will act as a static, non-movable system until melting begins in the crystalline phase, at about C (melting point Tm) It will take hours to melt all crystalline structures at temperatures of 18 C while it will melt rapidly at 24 C This allows for a wide range of processing temperatures for PET cores At a temperature of eg 15 C it allows a process time of days, a temperature of 18 C allows only a short process cycles of a couple of hours Most other foam cores such as PVC cores do not exhibit crystalline structure, their technical performance data changes dramatically above the Tg (Tg for PVC core is C), typically mechanical properties will deteriorate with increasing temperatures Cross linked PVC will show a better performance than linear PVC; but is still inferior to PET and it cannot recover once it has been heated above this critical temperature Standard PVC core cannot be processed above 9 C High temperature PVC core can be processed up to 13 C Mechanical properties as a function of temperature All materials are more or less affected by the ambient temperature Polymer materials such as foam cores tend to be more sensitive than conventional engineering materials, wood or metals Therefore it is crucial that the core material is evaluated in the temperature it is supposed to be processed and operated within ArmaFORM PET cores soften, strength and stiffness decrease, when heated just as all other foam cores but more slowly due to its crystalline structure allowing a wider operating and processing window than most other In the same way ArmaFORM PET cores stiffen and get stronger when temperature decrease but also lose a bit of ductility This is in line with other polymer materials As all mechanical properties are linked to each other they will have the same general behaviour when temperatures change The property that is easiest to test for different temperatures, from hot to cold, is the compression properties Compression samples do not rely on bonding the specimens to the backing plates as for tensile of shear tests, removing the influence from the bonding adhesive that in turn is temperature sensitive Therefore compression testing has been used to characterise the mechanical properties for ArmaFORM PET AC grade core according to ISO 844 The compression strength and modulus for ArmaFORM PET AC grade as a function of temperature from -4 C to 18 C is presented in figure 1 and 2 Armacell Benelux SA Rue des Trois Entités, 9 B-489 Thimister-Clermont Phone: +32 () infoarmaform@armacellcom wwwarmacell-foam-corescom

2 TEMPERATURE STABILITY ARMAFORM PET AC Relative Compressive Strength 14, 12, 1, 8, 6, 4, 2, Relative strength (%) AC grade PVC Standard, (C) Figure 1 Compression strength vs temperature Relative Compressive Modulus 14, 12, 1, 8, 6, 4, 2, Relative Modulus (%) AC grade PVC Standard, (C) Figure 2 Compression modulus vs temperature It can be noted that there are two areas of more interest for AC grade PET core material One is after the Tg is exceeded (8 C) and the core lose mechanical properties more rapidly until the crystalline network provide a cushion effect The second is above 18 C when the crystalline network also start to melt and the core soften even further Armacell Benelux SA Rue des Trois Entités, 9 B-489 Thimister-Clermont Phone: +32 () infoarmaform@armacellcom wwwarmacell-foam-corescom

3 Processing AC grade at elevated temperature When processing foam cores at elevated temperatures (close to or above their Tg) you always have to take into account the combination of time, temperature and pressure together with the density (compression strength) of the core to reach a good result The strength properties retained for AC grade are 34 % at 12 C and around 2 % at 18 C This might seem low but it will allow a processing time with minor dimensional changes at full vacuum according to figure 3-5 Generally the core will shrink slightly in thickness but the values stated can be taken as a worst case as these samples have been allowed to move unrestricted Normally this is not the case and preventing in-plane expansion will also minimize the thickness shrinkage The up going trend for the low densities at 18 C and 2 h can be explained It is simply the gas in the cells that try to expand when heated and resist the shrinkage that take place after the gas diffuses out This phenomenon can be seen with all closed cell foam cores at certain temperatures After the gas diffuses out the general thickness reduction trend is resumed with longer time Dimensional stability vs, 2h, 1 bar Figure 3 Thickness change as function of temperature and density at full vacuum for 2 h Armacell Benelux SA Rue des Trois Entités, 9 B-489 Thimister-Clermont Phone: +32 () infoarmaform@armacellcom wwwarmacell-foam-corescom

4 TEMPERATURE STABILITY ARMAFORM PET AC Dimensional stability vs, 24h, 1 bar -3-3,5-4 -4,5 Figure 4 Thickness change as function of temperature and density at full vacuum for 24 h Dimensional stability vs, 48h, 1 bar -3-3,5-4 -4,5 Figure 5 Thickness change as function of temperature and density at full vacuum for 48 h Armacell Benelux SA Rue des Trois Entités, 9 B-489 Thimister-Clermont Phone: +32 () infoarmaform@armacellcom wwwarmacell-foam-corescom

5 Avoiding creep effects All polymer materials are subjected to creep behavior if loaded at high levels for long periods of time At elevated temperatures ie during processing this can be accentuated as the core soften Again this is of course depending on the combination of time, temperature and pressure together with the density (compression strength) of the core In order to avoid creep problems when processing as a rule of thumb you require a safety factor of 3 on the compression strength of the core at the temperature in questions A simple example should illustrate, consider a high pressure processing at 25 bar and 1 C We want to check if AC 115 with compression strength of 18 MPa at room temperature is up to the task The strength retention of AC 115 at 1 C is just above 4 % ie the 4*18=72 MPa The pressure subjected to the core is 25 bar equals 25 MPa but with the safety factor of 3 that equals 25*3=75MPa As the design pressure of 75 MPa is higher than the compression strength of AC 115 of 72 MPa there is likely problems with creep unless the processing time can be kept short To avoid the creep problem it would be recommended to go to AC 135 instead that with compression strength of 4*25=1 MPa exceed the design pressure and creep is probably not an issue As always actual processing conditions and materials has to be tested to verify the suitability High pressure processing 25 bar at 1 C Saftey Factor = 3 25*3 = 75 MPa Checking Compression strength at room Temp Strength retention at 1 C AC 115 = 18 MPa 4% 4*18 = 72 MPa NON OK AC 135 = 25 MPa 4% 4*25 = 1 MPa OK Status : Technical Info 4 - May 211 Armacell provides this information as a technical service To the extent the information is derived from sources other than Armacell, Armacell is substantially, if not wholly, relying upon the other source(s) to provide accurate information Information provided as a result of Armacell s own technical analysis and testing is accurate to the extent of our knowledge and ability, using effective standardized methods and procedures Each user of these products, or information, should perform their own tests to determine the safety, fitness and suitability of the products, or combination of products, for any foreseeable purposes, applications and uses by the user and by any third party to which the user may convey the products Since Armacell cannot control the end of this product, Armacell does not guarantee that the user will obtain the same results as published in this document The data and information is provided as technical service, and the data and information are subject to change without notice Armacell Benelux SA Rue des Trois Entités, 9 B-489 Thimister-Clermont Phone: +32 () infoarmaform@armacellcom wwwarmacell-foam-corescom