A rubber additive made from cashew nut shells. Cardanol, an agricultural by-product of cashew nut shells, is a cheap and abundantly available renewable resource. In Industrial

& Engineering Chemistry Research (May 2013), researchers investigated the use of cardanol as an additive for natural rubber. Cardanol was grafted onto pieces of natural rubber latex and the chemical properties examined.

One property of interest is the grafting efficiency (measured as a percentage) of the chemical process. The researchers manipulated several independent variables in the chemical process: x1 = initiator concentration (parts per hundred resin), x2 = cardanol concentration (parts per hundred resin), x3 = reaction temperature (degrees Celsius), and x4 = reaction time (hours). Values of these variables, as well as the dependent variable y = grafting efficiency, were recorded for a sample of n = 9 chemical runs. The data are provided in the accompanying table. A MINITAB analysis of the first-order model, E1y12 = b0 + b1x1 + b2x2 + b3x3 + b4x4, is also shown.

a. Conduct a test of overall model adequacy. Use a = .10.

b. Interpret practically the value of R2a

c. Interpret practically the value of s.

d. Find and interpret a 90% confidence interval for b3.

e. Conduct a test of H0: b4 = 0. What do you conclude?

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Run GE (V) IC (X1) CC (x2) RTEMP (X3) RTIME (X4) 1 81.94 1 2 52.38 1 3 54.62 1 15 4 84.92 2 5 78.93 6 36.47 2 7 67.79 8 43.96 9 42.85 22333 2 10 15 3 3 10 3 15 SOURCES 5 35 6 10 50 65 10 5 50 10 65 35 5 65 35 50 89968896 10