in a deformed state prevails the percent relaxation value is defined as the difference between the 25 kilogram load and the load at equilibrium divided by the 25 kilogram load and multiplied by 100 fig1 illustrates the relationship graphically and represents a plot of the compression load versus time the force of the instron head is gradually increased to the value of p over a period of time and p may be selected arbitrarily e g 25 kilograms after the board is allowed to equilibrate it reaches a constant compression load of the value r percent relaxation value is then defined as p r p u00d7 100 it will be understood that the lower the value for percent relaxation the higher the stability of the board under wet conditions and conversely the higher the percent relaxation value the the lower the wet stability and the more likely the board will be to deform under pressure when wet a series of sample boards are prepared from hydrocolloidal fibrous material made in accordance with example iii of the aforementioned u s pat no 3 889 678 this material is a cellulose graft copolymer consisting of a cellulose backbone having grafted thereto hydrolyzed polymer moieties of poly acrylonitrile and poly ethyl acrylate by combining wood pulp acrylonitrile and ethyl acrylate as the starting materials in the following weight properties 1 part wood pulp to 1 40 parts ethyl acrylate to 0 8 parts acrylonitrile this hydrocolloidal material is in fibrous form the fibers having an average fiber length of approximately 0 89 millimeters in accordance with aforementioned u s pat no 3 889 678 the grafted material is subjected to a hydrolysis step table 2 sets out the.