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PMI foams with outstanding characteristics  #10 (56), 2007

Evonik IndustriesTwo new types of constructional PMI foams of ROHACELL® brand specially designed by specialists of Evonik Industries Company for resin infusion processes have become available now. In comparison to standard products the new foam materials have smaller cells sizes, which significantly reduces surface resin absorption by the core of multi-layer constructions

Degrees of surface oil absorption by ROHACELL® materials.One of the previous company’s products – ROHACELL® WF-HT – possessed such an important property as lack of substantial creeping under processing up to 180°C/0.5 MPa and density of 75 kg/m3. However the material showed moderate oil absorption of 0.4 l/m2, which can be critical for the product weight. For that reason Evonik Industries Company developed a method for adaptation of medium-diameter cells of ROHACELL® in order to lower the surface oil absorption at the same time preserving excellent thermomechanical properties of ROHACELL® WF.
As a result two new types of ROHACELL® materials have been designed:
RIST with structural resin infusion. This foam material is characterized by medium-sized cells and lower resin absorption, keeping up high adhesion to the surface;
RIMA with optimization of resin infusion technology. This foam material ensures minor surface resin uptake, but has weaker adhesion between the core and the surface.
Photomicrograph of cells of various ROHACELL® foam materialsPictures 1 and 2 show that a thinner cell structure of ROHACELL® RIST and RIMA actually leads to significant reduction in the surface oil absorption. Due to fine cell structure mechanical properties of ROHACELL® RIMA surpass similar properties of WF (Table 2).
Alongside reduced surface resin uptake as cell size decreased, peel resistance indices in RIMA brand also achieved a very low level. It was proved by all twist tests: foam material broke up in the layer adjoining the surface; but there was no destruction of adhesion between the foam material and resin, which proves outstanding surface adhesion characteristics of the new PMI foams.

Table 1. Mechanical properties of some ROHACELL® foam materials

ROHACELL 51 51  71 71 71  110  110
  WF RIMA WF RIST RIMA WF  RIMA
Density, kg/m3 Density 52  42 75 75 65 110  93 
Compressive strength, MPa 0,8 0,79 1,7 1,75 1,67 3,6  
Tensile strength, MPa 1,6 1,65 2,2   2,58 3,7   3,97
Elastic modulus, MPa 75 59 105   90  180  139
Elongation at break, % 3 9,8 3   10,5  3  8,4
Heat distortion temperature, °C 205 220 200   225 200   

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