Hi Guest,

White patches or entire leaves on a red-leafed Acer palmatum are normally a sign of sun scorch. They should be kept in a bright location (to maintain the red colouration) but protected from direct bright sunlight, particularly during the hottest part of the day.

The limpness may have more to do with the plant drying out in the recent near-drought. Make sure you keep the roots cool, moist and well-drained for best results.

Good answer, plus, try to position it away from drying winds which will dessicate the leaves, drying them faster than the plant can replenish them with water sent up from the roots. Rapid transpiration is the quickest way to crisp up the leaves of acers. All of mine are in a south facing position, but sheltered by taller tres and shrubs behind them, so air movement is kept to a minimum. Friendof mine, Peter Catt, Liss Forest Nursery, grows his acers in a glasshouse, full sun, and they feel biscuit dry in the pots, but all in beautiful condition.
Phil J