htmltable slow redraw in .net 4.0

Question

Hi i'm using an htmltable that is refreshed when a textbox change.

For refresh it i'm using this code:

HtmlTableRow tableRow;
HtmlTableCell tableCell;

    for (int i = 0; i < 50; i++)
    {
        tableRow = new HtmlTableRow();
        tableCell = new HtmlTableCell();
        tableCell.InnerHtml = i.ToString();
        tableRow.Cells.Add(tableCell);
        tableCell = new HtmlTableCell();
        tableCell.InnerHtml = i.ToString();
        tableRow.Cells.Add(tableCell);
        tableCell = new HtmlTableCell();
        tableCell.InnerHtml = i.ToString();
        tableRow.Cells.Add(tableCell);
        tableCell = new HtmlTableCell();
        tableCell.InnerHtml = i.ToString();
        tableRow.Cells.Add(tableCell);
        tableCell = new HtmlTableCell();
        tableCell.InnerHtml = i.ToString();
        tableRow.Cells.Add(tableCell);
        tableMissioniDestinazioni.Rows.Add(tableRow);
    }

with .net 3.5 it always worked. but with .net 4.0 when the textboxvalue is bigger then 20 it's very slow.

Why?

How can i do to speed it?