You need to use SuiteScript instead of a workflow to implement this functionality. A scheduled script would be best if you need to send the emails on a regular basis. You may follow these steps as a guide:
1. Retrieve the value of the text field with nlapiGetFieldValue or getFieldValue.
2. Split the retrieved text field value using your delimiter. If the string is comma-delimited, you might use something like
var arrEmails = txtEmails.split(‘,’);
3. Pass this array as the fifth parameter (cc) to nlapiSendEmail like so:
nlapiSendEmail(-5, your_recipient, “Email Subject”, “Email message here…”, arrEmails);
I hope this helps!