Fabrication of crystalline articles of aromatic polycarbonate by hot powder-compaction

Abstract

Polycarbonate is well known for forming amorphous, transparent, and exceptionally tough articles by conventional methods such as injection molding and extrusion. It is not possible to extrude polycarbonate from the melt into crystalline, shaped articles. A novel method to fabricate crystalline polycarbonate articles from acetone‐crystallized powder was devised. The method was adapted from powder metallurgy and it involved compacting acetone‐crystallized polycarbonate powder above the glass transition temperature (Tg) and below the melting peak temperature (Tm). The hot powder‐compaction process yielded shaped articles, which retained the crystallinity of the original polycarbonate powder. Although the crystallinity of the powder and the articles was less than 20%, surprisingly the articles were non‐sticking above the Tg and so could be released from the mold at the compaction temperature. Furthermore, the crystalline polycarbonate articles had a Vicat softening temperature above 180°C, excellent shape and dimension retention above Tg, increased hardness, as well as resistance to acetone and other solvents. That is, the properties were different from those of conventional amorphous polycarbonate articles. POLYM. ENG. SCI., 57:581–590, 2017. © 2016 Society of Plastics Engineers

Evaluation of poly(ethylene terephthalate) powder as a material for selective laser sintering, and characterization of printed part

“…With polymers, this will always leave a certain amount of voids. In hot powder compaction , the pressure during sintering prevents full melting of the PET powder, and hence a crystallinity similar or higher than the original powder is obtained in the finished article, as Fig. c proves.…”

“…It is worth comparing SLS of polymers with another powder‐sintering process for making net shapes from semi‐crystalline polymer powders. Hot powder compaction is proposed by Ahmad and Bashir as a viable fabrication method to make net shape articles from semi‐crystalline polymer powders, in an analogous manner as powder metallurgy. This is a non AM method as it requires tooling (heated dies and punches), but it is based on compacting and sintering crystalline powder without full melting.…”

“…However, unlike SLS, the part fabricated via hot powder compaction is made in seconds or minutes instead of hours. Moreover, unlike SLS, the part does not have porosity problems . This is because in hot powder compaction, heat and pressure are applied together; that is, it is hot sintering with pressure.…”