Dimensional recovery of cold‐rolled polycarbonate

SynopsisThermal shrinkage of highly hot-drawn and quenched poly(methy1 methacrylate) and polycarbonate of bisphenol A were measured. PMMA shows three-step thermal shrinkage under suitable experimental conditions above its glass transition temperature (Tg). Polycarbonate exhibits four kinds of molecular relaxation associated with shrinkage around and above its Tg. The effect of hot-drawing and quenching conditions on shrinking behavior is discussed. Almost all of the molecular relaxations are observed above Tg. The molecular origins of the relaxations are discussed in relation with the so-called T11 transitions of polymers.

Section: Resultsmentioning

confidence: 99%

Multiple molecular relaxations of hot‐drawn and quenched polymers above their glass transition temperatures

Kato¹,

Yanagihara²

1981

A thermomechanical investigation of highly cold‐drawn polycarbonate

Kato¹,

Kambe²

1978

SynopsisA new technique detecting molecular motions in drawn polymers was applied to highly cold-drawn polycarbonate of bisphenol A. It is shown that the sample exhibits thermal shrinkage in three steps with the temperature increase up to above the glass transition temperature. The molecular relaxation at the highest temperature is due to the glass transition. The other two molecular motions a t the lower temperature are those of main chain in the glassy state and they correspond to the molecular motions as revealed in dielectric measurement by Sacher.' By using the general theory of the thermal analysis by Ozawa,2 the apparent activation energies of these molecular motions were obtained for the highest temperature 110 kcal/mole, and for the lowest temperature, 33.5 kcal/mole. The impact strength and the cold workability of this polymer are also discussed in relation to these molecular motions.

The influence of thermal history on internal stress distributions in sheets of PMMA and polycarbonate

Saffell

Windle

1980

The through‐thickness birefringent patterns (nx – nz) of PMMA and polycarbonate (PC) are measured as a function of thickness, cooling rate, and annealing time. A method is demonstrated for separating the elastic stress from the residual birefringence. The residual birefringence is explained as the residual orientation induced when cooling through the galss transition. The shape of the elastic (tempering) stress distribution is apparently independent of the cooling rate and annealing time, the choice of polymer, and the sheet thickness. The magnitude of the tempering stres is dependent on cooling rate but nearly independent of choice of polymer and sheet thickness. The decays of both the tempering stress and the residual orientation are measured as a function of annealing time at 120°C for polycarbonate. The measured birefringence decays only slightly; however, the elastic tempering stress reverts, on annealing, to permanent (anelastic) orientational strain. The tempering stress at the sheet surface is not an adequate criterion for defining toughness in polycarbonate.