In Chapter Nine of The Grapes of Wrath, how does Steinbeck use the Joad's departure for California to solidify his characterization of each family member?
I think your question is somewhat confused. Chapter Nine forms one of many intercalary chapters where the focus shifts from the Joad family in particular to tenant farmers in general, exploring how they prepared for the exodus to California. By assuming the voice of the typical tenant farmer, Steinbeck reveals the way that they have to pawn their possessions to raise money and because they are unable to take everything with them. This of course means that these farmers are open to the exploitation and abuse of the brokers, who know that the farmers must sell quickly and are not able to bargain in order to get a fair price. They are then forced to return to their wives with the paltry amount of money that they were able to raise from their belongings, leaving their wives to mourn the loss of treasured possessions.
This chapter, although it does not focus on the Joad family, can be used to understand them better. The way in which the pawnbrokers and the crooked car salesmen are presented introduces a central theme of man's inhumanity to man, which is of course something that the Joads are shown to fight against for the entire narrative. Unfortunately, the rather depressing message of the text is that those who have power over others below them will take any opportunity to exploit and abuse that power to enrich themselves and improve their own position. This general trend of course contradicts the belief of Jim Casy that men must act for the good of all men. In his rather bleak presentation of humanity, Steinbeck suggests that an inability to act based on charity and selflessness leaves us lacking hope and a future. Note what one farmer says to the pawnbroker who cheats him:
You cut us down, and soon you will be cut down and there’ll be none of us to save you.
Thus, although this chapter does not focus on the Joads, it does explore the theme of moral justice and injustice, that helps us to understand the forces against with the Joads battle and their keen commitment to charity and love.