Solid‐state processing of polymer powders through compaction and sintering has potential advantages over conventional polymer processing methods; however, pressureless sintering of compacted polymer powders has often been unsuccessful. Room temperature compaction of polycarbonate (PC) powder was studied in an effort to better understand the fundamental mechanisms that control polymer compaction and sintering. It was found that differences in the degree of physical aging affect the compaction behavior of PC powder. The results presented in this paper show that the degree of physical aging of thermoplastic polymer powders, which can be influenced by commonly used powder handling operations such as drying and long term storage, can ultimately affect the ability of the powder to be successfully compacted at room temperature.

Solid‐state processing of polymer powders through compaction and sintering has potential advantages over conventional polymer processing methods. However, pressureless sintering of compacted polymer powders has been unsuccessful. In a previous paper (2), room temperature compaction of polycarbonate powder was studied to better understand the fundamental mechanisms that control polymer compaction. This paper focuses on the pressureless sintering of room temperature compacted polycarbonate powder. Thermomechanical analysis was used to characterize the dependence of dimensional recovery on time, temperature, and compaction pressure for compacts formed from both aged and unaged polycarbonate. It was found that all polycarbonate compacts exhibited irreversible expansion when heated to relatively low temperatures (∼ 50°C), with large‐scale expansion occurring near its glass transition temperature. It was concluded that irreversible expansion of polymer compacts is driven by entropic factors. Therefore, parameters that affect the degree of particle deformation during compaction also affect the degree of dimensional recovery that occurs during pressureless sintering.

In order to take advantage of the potential benefits provided by solid-state processing of thermoplastic polymers (1-3). conventional compaction and sintering techniques must be modified to prevent large-scale recovery (or dimensional changes) that occur upon heating polymeric compacts above their respective glass transition temperature (Tg). Two solid-state processing techniques that have the potential for reducing recovery, hot compaction and consolidation (sintering polymeric compacts under applied pressure), were investigated in this study. The results presented in this paper show that while hot compaction (below T,) does not prevent large-scale recovery, consolidation using pressures as low as 50 kPa (7.3 psi) did significantly reduce recovery in polycarbonate compacts. WTRODUCTIONhis paper is the second in a series of studies on

Defects in adhesive bonds in composite products are difficult to detect because of the nonconductive and nonmagnetic properties of polymeric materials. However, intelligent bonding can be performed by adding a small amount of sensoiy particles such as ferromagnetic powder to an adhesive so that it will respond to an external magnetic stimulus. Useful indication parameters can then be extracted from the response to describe the condition of the bond. One of the difficulties with this technique is activating the particles effectively to make the response of the adhesive detectable.Pr material relative permeability of tagging particle 400

Applications ofpolymeric adhesives injoining different materials have necessitated quantitativehealth inspection of adhesive joints (coverage, state of cure, adhesive strength, location of voids, etc.). A new in-situ sensory method has been proposed in this paper to inspect the amount and distribution of the critical constituents of polymers and to measure the characteristic parameters (complex Young's modulus and damping). In this technique, ferromagnetic particles have been embedded in a polymeric matrix, similar to a particle-reinforced composite. The dynamic signatures extracted from the tests as a result of magnetic excitation of the embedded ferromagnetic particles are used to evaluate the complex Young's modulus of the host polymers. Moreover, the amplitude of the frequency response is utilized to identify the amount and distribution of embedded particles in polymeric materials or adhesive joints. The results predicted from the theoretical model agree well with the experimental results. The theoretical analyses and the experimental work conducted have demonstrated the utility of the sensory technique presented for in-service health interrogation.