To stay clear of having your business getting labelled as a spammer, send out personal emails with NO offers, promotions or anything sale-sy.
If there is anything you can use to customize your email, such as recent tweets of a purchase manager, use them in your email. Also, try sending a short email to initiate a relationship, not to push what you are selling. Instead of sending a brochure or an email with tons of red and highlighted text, try to schedule a phone call with them. During the call, you can then offer to send over some samples for their evaluation.
And back to your original question about subject lines, they should always be personal, related to the recipient as well as the content. For example, if you know the company name of a purchase manager, you can use subject lines like "How to Improve Acme Co.'s Material Rejection Rates?" or even "Hi <purchase manager's first name>". Since you are trying to initiate a conversation and not sell something in your first email, the second subject line may work!
You should know your prospects and the words they use best so use the knowledge to your advantage. And of course, when it comes to subject lines, it is always good to keep track on what's working and what's not.