$names = array();
for ($i = 0; $i < 100; $i++) {
    $names[] = $i;
}

$parts = count($names) / 20;

$j = 0;

for ($i = 0; $i < $parts; $i++) {
    echo "Part" . $i."<br>";
    $newarray = array_slice($names, $j, 20);
    for ($i = 0; $i < count($newarray); $i++) {
        echo $i;
    }
    $j = $j + 20;
}

$j = 0;

for ($i = 0; $i < $parts; $i++) {
    echo "Part" . $i."<br>";
    $newarray = array_slice($names, $j, 20);
    for ($i1 = 0; $i1 < count($newarray); $i1++) {
        echo $i1;
    }
    $j = $j + 20;
}