Runnable thread stuck/freezes the ui after continuously loading webview

Question

Due to loading webview coninuously using my runnable thread in android , my application freezes after some time. below is my code:

mUpdateTimeTask = new Runnable() {
          public void run() {

              System.gc();
              if(i%15==0)
              {
                  clearApplicationData();
                  cookieManager.removeAllCookie();

              }
              browser.clearCache(true);
              browser2.clearCache(true);
              browser3.clearCache(true);
              browser4.clearCache(true);
              browser5.clearCache(true);
              try{
              browser.loadUrl("file:///android_asset/go.swf");
              Thread.sleep(100);
              browser2.loadUrl("file:///android_asset/go.swf");
              Thread.sleep(100);
              browser3.loadUrl("file:///android_asset/go.swf");
              Thread.sleep(100);
              browser4.loadUrl("file:///android_asset/go.swf");
              Thread.sleep(100);
              browser5.loadUrl("file:///android_asset/go.swf");
              }
              catch(Exception e)
              {
                  Log.d("TAG ERROr","-----------------------"+e.toString());
              }

          i=i+1;
          mHandler.postDelayed(this, 20000);
          }
       };
       new Thread(mUpdateTimeTask).start();