The newest growth at the top of your Ti plant still looks healthy. Also, the brown foliage looks a bit soft and pliable, not stiff. If so, then I will guess a bacterial or fungal infection has hit the oldest leaves closest to the soil. This is usually from too much water, poor drainage or the pot sitting in a saucer of water. I suggest you remove all brown leaves and give the plant more sunshine and air and less water. Do not let this plant sit in full sun even indoors as it could sunburn. A location with just morning sun is best. You might also consider repotting the plant using fresh potting soil and a container with good drainage holes so that when you water the liquid runs through the soil quickly. Then empty any water that collects in the saucer under the plant or better yet water the plant in the sink. I think your plant will recover. Keep growing, Marianne Binetti