(361g) Near Net-Shape Manufacturing of Solid-State Polymer Blends | AIChE

(361g) Near Net-Shape Manufacturing of Solid-State Polymer Blends

Authors 

Schexnaydre, R. - Presenter, Tulane University
Mitchell, B. S. - Presenter, Tulane University


Conventional melt and solution processes cannot overcome some of the technical barriers inherent in blending polymers. Most polymers are inherently immiscible with respect to each other, and the kinetic and thermodynamic limitations of chemical compatibilizers do not sufficiently prevent dispersed phases from coalescing and thus inducing macroscopic phase separation. Near net-shape manufacturing (NNSM) can provide a ?solventless' solid-state route that could potentially overcome the tendency of dispersed phase domain coarsening by a combination of two processes.

This novel technique will be used to accomplish the ultimate goal of compatibilization of polymer pairs that are immiscible and are likely to phase separate. This objective is proposed to be realized by a series of processing steps. First, the combination of intimate mixing at the microscale and nanoscale via particle size reduction and amorphization in the mechanical alloying (MA) step can effectively disperse the fine crystalline domains by physically-induced adhesion at small scales. The second step is consolidation of milled powders via mechanical pressing into thin membranes and subsequent hot isostatic pressing (HIP) at room temperature. The proof of compatibility will be retention of dispersed-phase domain size upon isothermal annealing experiments post-HIP, i.e., domain coarsening should be less prevalent than for conventionally-blended polymers.

Preliminary experiments for homopolymers confirmed the validity of NNSM. For example, ultrafine particles of poly (p-phenylene), a high temperature thermoplastic, were produced with mechanical milling. Cryogenic milling introduced much less contamination and amorphized polymers more than ball milling, a phenomenon supported by X-ray diffraction (XRD) and differential scanning calorimetry (DSC) of various polymers such as polyethylene oxide, polyvinylpyrrolidone, and polyethylene terephthalate. Both types of milling negligibly affect molecular weight, and the amount of amorphization is dependent on the initial crystallinity of the polymer ? both well-supported by literature.

Both spectroscopic and microscopic characterization techniques have been used to probe the morphology and dispersed-phase domain sizes of various blends. Thermal analysis techniques also indicate the level of ?cooperation' between blend phases. Traditional microscopic methods such as transmission electron microscopy (TEM) and scanning electron microscopy (SEM) have superior resolution and have produced images showing the domain and particle sizes for various polymers. However, inherent poor contrast and tedious sample preparation steps for both of these characterization routes have allowed Fourier-transform infrared (FT-IR) spectroscopy to become a complement in investigation of polymer blends. Specifically, synchrotron FT-IR's advantages of phase domain mapping can provide an additional tool in understanding driving forces for blend compatibilization.

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