There is a growing demand for rigid vinyl foam as a wood replacement in window frames, blinds, trimming and other applications. While rigid vinyl foam has existed for many years, additional understanding of its processability and required conditions for good quality extruded profile would be helpful. This paper examines the effect of extrusion conditions, such as melt temperature, screw speed, and drawdown on process morphology of rigid vinyl foam and the properties of the extruded profile, including density, cell structure, and surface appearance.

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ABSTRACT:Poly(vinyl chloride) (PVC) plastisol is a suspension of small particles of PVC resin in plasticizer. The processing of plastisol typically involves flow at room temperature during coating or mold filling, and gelation and fusion as the plastisol is heated to form the final product. This paper explores the effect of the particle size distribution on the gelation and fusion behavior. For this purpose a commercial PVC resin was air-classified into fractions of different particle size. Samples were then reconstituted to have known particle size distributions. Particular emphasis is placed on the effect of the fine particle fraction on the material behavior. The progress of gelation and fusion were followed by measurement of the viscoelastic properties as a function of treatment temperature using a mechanical spectrometer. Characteristic changes in the viscoelastic behavior were associated with changes in morphology, observed with a scanning electron microscope, enabling qualitative discrimination of the gelation and fusion processes. The larger fraction of fine particles gave higher values of G' and G". It seems that the fine particles promote the interparticulate bonding, when the particles start fusing together.KEY WORDS Poly(vinyl chloride) I Plastisol I Particle Size Distribution I Gelation-Fusion I Particulate Morphology I Viscoelastic Properties 1 Both the average particle size and the particle size distribution of poly(vinyl chloride) (PVC) dispersion resins have been recognized as important material variables pertinent to PVC plastisol behavior. The flow behavior at room temperature is profoundly influenced by these variables. Therefore, they are important in regard to processability. The types of flow behavior encountered in these systems, such as thixotropy, shear-thinning and dilatancy have been investigated previously. 1 The oscillatory measurements were also carried out to characterize the dynamic responses. 2 On the other hand, less attention was paid to the effect of particle size and size distribution on gelation and fusion. Since gelation and fusion are also important steps in plastisol processing, we have undertaken this study. gelation and fusion. 5 These observations elucidated the mechanism of the diffusion of plasticizer into resin particles, the presence and disappearance of particulate structure and the temperature range of the melting of the PVC crystallites. In addition, the progress of interparticle bonding was postulated to explain the accompanying development of mechanical strength.Our previous studies demonstrated the effectiveness of viscoelastic measurements for characterizing gelation and fusion behavior. 3 -5 Morphology was also examined of samples taken at different stages of When the plasticizer is taken up by the resin particles, a large amount of interparticle voids are present; these voids disappear, of course, when the particulate structure disappears. However, some defects are present up until the fusion is complete; the latter state is reached when the mechanical ...

Damage to poly (vinyl chloride) (PVC) compounds due to thermal degradation during processing has an important influence on its subsequent weatherability. High melt temperatures and/or high residence times cause white PVC to become more yellow and colored PVC to fade and bleach more upon weathering. If high melt temperatures are used, then short residence times are needed to maintain excellent weatherability. In addition to careful consideration of extrusion conditions, stream‐lined equipment is necessary to produce extrudate of uniform thermal history. Also, relatively high thermal stabilizer levels help reduce thermal damage and, therefore, improve weatherability. Impact resistance is better retained when processing occurs at higher melt temperatures. A reasonable compromise between extrusion rate and temperature must be reached to provide for adequate color and impact retention.

Recent morphological studies of plasticized and unplasticified poly (vinyl chloride) (PVC) are reviewed. Suspension polymerized PVC contains particles in a number of different size ranges 100-200A, 1000-5000A, 1~ and larger. The larger size particles are broken down during plasticization but both the 1OOA and the lOOOA suspension articles retain their idenparticles is a function of the processing conditions. In particular, the size of the lOOA particle increases with plasticizer content and is most distinct as characterized both by small angle x-ray scattering and electron microscopy for milling temperatures in the 160-170°C. range. Consideration is given to the effect of these particles, their structure, and interrelationship on the rheological properties of the resins. tity. The visibility, and presumaby, Y coalescence of these