unity - I have a problem rotating a 2D game object after collision

I'm developing a simple flip game where a cube flips and the bar a it collides with should start rotating after collision. Most snips involve destroying an object, but that's not my case.

Here is my code:

using UnityEngine;


public class CheckI : MonoBehaviour
{
    float x;
    public Rigidbody2D rb2d;

    void OnCollisionEnter2D(Collision2D col)
    {
        if (col.gameObject.tag == "bar")
        {

            x += Time.deltaTime * -10;
            transform.rotation = Quaternion.Euler(0, 0, x);
        }
    }
}

How do I start rotation after collision?