Abstract
The strength of laminated plastics derives mainly from the fibrous reinforcement, but the fibres, being arranged in layers, cannot contribute to the interlaminar strength. The consequent weakness is revealed by a low crossโtensile strength and a low shear strength parallel to the laminations. Three methods of test which have been used pith laminates ยผ in thick are described and compared with material greater than ยผ in. in thickness, two additional tests may be employed.
Certain variables in the preparation of phenolicโbonded laminates are shown not to be critical, but interlaminar of strength in common with other properties of reinforced plastics is sensitive to variations in the moisture content of the impregnated reinforcement at the time of pressing.
The interlaminar strength of voidless products made from a phรจnolโformaldehyde resin in alcoholic solution with absorbent paper or scoured fabrics is substantially constant over the range of resin content likely to be used in practice. With both types of reinforcement the limiting strength of the resin itself is approachedโbut not fully attainedโat a resin content of 27%. There is no essential difference between the strengths obtained with scoured fabrics or absorbent paper.
The beneficial effects of desizing and scouring are conclusively proved. While the scouring process used does not appear to be highly critical, desizing by itself is not an adequate preโtreatment. Absence of twist in the threads of a fabric does not contribute to higher interlaminar strength.