The manufacture of certain types of disposable plastic containers generally involves welding one or more pre-formed polymer components together.  For example, a pouch and fitment assembly similar to those shown in FIG.  1 can be assembled from two sheets of a flexible polymer material that are fused or welded together around their periphery to form a pouch and a plastic fitment that is joined to the pouch, either at an end, at a corner, or on one face of the pouch.  The terms “fusing” and “welding” as used herein refer to any process by which a sealed connection is formed between two polymer components. 
A fitment can include a reusable cap, for example a screw cap, for opening and then resealing the pouch or can alternatively be closed with a one-time seal that a user breaks to access the pouch contents.  The term “fitment” as used herein is intended to refer broadly to one or more of a spout, valve, handle, dispenser, cap or other rigid feature that is physically sealed or built into a liner, bag, pouch, or other packaging container.  A fitment can be formed from one or more pieces that can be movable relative to each other and/or to the packaging container to which the fitment is attached.  Other openings can be provided for accessing or dispensing the contents of a packaging container, such as for example a foil patch or other orifice that can be punctured with a straw or a removable portion of the packaging container that can be ripped off or removed via a tear cord.  Heat sealing, ultrasonic welding, or other comparable techniques can be used to seal the flexible polymer to itself and to the fitment.