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Thermoformability study of virgin and regrind high impact polystyrene coextruded sheets: Influence of the number of processing cycles on the processing parameters
Author(s) -
Soriano Florentino,
Morales Graciela,
de León Ramón Díaz,
Belmontes Felipe Avalos
Publication year - 2006
Publication title -
polymer engineering and science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.503
H-Index - 111
eISSN - 1548-2634
pISSN - 0032-3888
DOI - 10.1002/pen.20502
Subject(s) - thermoforming , mold , materials science , polystyrene , composite material , materials processing , polymer , process engineering , engineering
High impact polystyrene was extruded repeatedly at 220°C and thermoformed under different heat time (Ht), plug assist time (PAt), mold time (Mt), and mold temperature (MT). The optimum thermoforming process conditions were determined for a material processed in one cycle, using an experimental design of the four variables mentioned before at two levels. Mt has no influence on the coefficient of wall thickness variation (CV), while the rest of the variables present a noticeable influence on CV, and they can be modified to obtain lower values of CV (i.e. CV = 1.3, using Ht = 46 s, PAt = 2.5 s, and MT = 80°C). These conditions were then employed for a material processed under six cycles, resulting in an increase in the CV value to 3.5. The normalized thickness (NT) of HIPS with one and six processing cycles was also evaluated. It depends on Ht, Mt, and PAt. With the values of the calculated parameters for CV, it was possible to obtain NT values close to 1, using a material processed one cycle. The NT value obtained for six cycles processed HIPS was far from unity. The changes on thermoforming variables' responses are a consequence of the changes occurred in HIPS inner structure. POLYM. ENG. SCI. 46:503–509, 2006. © 2006 Society of Plastics Engineers.