Formulating for rigid PVC using multivariate analysis

The wide range of lubricants available for rigid PVC, and their complex interactions or synergisms, has meant that the formulator has often had to rely more on quantitative experience, however incomplete, rather than on quantitative data. Multivariate analysis offers the possibility of investigating lubricants and fillers with a relatively small number of rheological experiments and defining their role in a wide range of formulations. A computer program and associated methodology has been developed that allows up to five formulations or fusion parameters to be examined with a maximum of just thirty-three torque rheometry experiments. The technique generates both first and second order coefficients for each parameter, coefficients that quantify all possible pair interactions, and applies statistical techniques to evaluate the significance of each coefficient. The levels of “internal” and “external” lubricants and fillers, as well as the charge volume and shear rate in the rheometer, have been correlated with fusion peak time and torque, equilibrium torque and melt temperature and other features of the fusion curve. The data are also presented in a series of graphs so that subsequent formulation can be done by interpolation, without further experimentation. The result have sometimes been unexpected and can help in understanding the role of the various additives in the extrusion of rigid PVC.     

Changes in rheological properties of polyvinyl chloride plastisols with storage time

In this study, the changes in the rheological curves of polyvinyl chloride (PVC) plastisols with increasing storage time and the factors affecting these changes were studied. The results show that with increasing storage time, all the “viscosity–temperature” and “viscosity–time” rheological curves of PVC plastisols exhibit nonnormal distribution change trends, that is, the viscosity first decreases, and then changes from slow increasing to rapid increasing, forming a shoulder peak, reaches to the maximum value and gradually decreases. With increasing storage time, the complex viscosities of PVC plastisols increased generally in the first, the second, and the fourth stages, and the gelation process shortened in the third stage. The first and second stages of the viscosity changes reflect the “time–temperature” equivalence principle of PVC plastisol in suspension stage. However, the maximum viscosity of PVC plastisol corresponding to temperature Tη_max does not change with increasing storage time.     

Lubrication mechanism of poly(vinyl chloride) compounds: Changes upon PVC fusion (gelation)

Poly(vinyl chloride) (PVC) compounds perform best with adequate metal lubrication and polymer‐to‐polymer lubrication of PVC primary particle flow units. Much of the mechanism for the lubrication of PVC has been elucidated over the years. One point has not been completely understood, which is the “lubricant failure” at higher processing temperatures where the compound is known to become less ductile. This result is contrary to what might be expected with better PVC fusion (gelation). This article discusses the mechanism involved, which is lubricant inversion, where the lubricant goes from the continuous phase, as a surfactant coating all the PVC primary particle flow units at lower melt temperatures, to become the discontinuous phase at higher melt temperatures. J. VINYL. ADDIT. TECHNOL., 11:57–62, 2005. © 2005 Society of Plastics Engineers     

Nanoscopic characterization of a plastisol gelation and fusion process utilizing scanning electron microscopy and atomic force microscopy

Understanding the physical properties associated with the gelation and fusion of a PVC plastisol will help to improve process efficiency. Plastisol gelation and fusion were characterized by using both scanning electron microscopy (SEM) and atomic force microscopy (AFM) and were compared with the tensile properties developed at various temperatures. Both SEM and AFM showed good agreement during the early stages of gelation. However, AFM continued to show particle boundaries during the latter stages of gelation and fusion that provided a more nearly accurate comparison with the resulting tensile properties. J. VINYL ADDIT. TECHNOL., 2008. © 2008 Society of Plastics Engineers.     

Evaluation of secondary lubricants for rigid PVC extrusion

A common system of primary lubricants in rigid PVC extrusion compounds is calcium stearate plus paraffin wax. Secondary lubricants are frequently added to this system at low concentrations with the intention of improving such properties as metal release, thermal stability, plateout, extrudate surface appearance, etc. This paper discusses the results of laboratory studies designed to evaluate the contribution to these properties of two commonly used secondary lubricants: AC629A, an oxidized low molecular weight polyethylene, and K175, an acrylic “lubricating processing aid.” Surprisingly, the testing showed little improvement in performance when these auxiliary lubricants were added.     

Influence of surfactant properties on thermal behavior and sol–gel transitions in surfactant‐HPMC mixtures

Four surfactants, namely, sodium n‐decyl sulfate (SDeS), sodium n‐hexadecyl sulfate (SHS), sodium n‐dodecyl sulfate (SDS), and Triton X‐100, were used as additives to study thermal behavior and sol–gel transformations in dilute aqueous hydroxypropyl methyl cellulose (HPMC)/surfactant mixtures using micro‐differential scanning calorimetry. The influence of anionic surfactant, SDS on the gelation varied with SDS concentration where the sol–gel transition started at a higher temperature. Shape of the thermograms changed from single mode to dual mode at the SDS concentration of 6 mM and higher. SDeS and SHS, however, resulted in “salt‐in” effect of a different magnitude during gelation. Triton X‐100, being a non‐ionic surfactant, showed a minor “salt‐out” effect on the thermo‐gelation process. On the basis of different thermal behavior of anionic and non‐ionic surfactant/HPMC systems, a mechanism is proposed explaining how the chemical structure and electro‐charge of the surfactants affect the polymer/surfactant binding and polymer/polymer aggregation because of hydrophobic interaction during the sol–gel transition. © 2009 Wiley Periodicals, Inc. Journal of Applied Polymer Science, 2009     

Fluorescence polarization study of the curing process of epoxide with aminimide

The curing process of epoxide (Epikote 828, EK) with aminimide (trimethylamine valerimide, TMAV) was studied by a fluorescence polarization method. Two types of probe molecules were used: One was perylene (PE), which was just physically incorporated into the curing mixture and termed as the “extrinsic” probe, and the other was fluorescent product(s) formed during curing of EK with TMAV, which was termed as the “intrinsic” probe. Extraction experiments revealed that the “intrinsic” probe was covalently incorporated into the crosslinked matrix. No emission was observed for the “intrinsic” probe before heating, but its intensity increased with curing at 150°C. Fluorescence anisotropy (r) of both EK/TMAV/PE and EK/TMAV systems increased monotonically with curing time at the initial stage and then remained nearly constant. This means that at the early stage of curing the network becomes rigid enough to restrict rotational diffusion of the probe molecules. Calculated r values for the “extrinsic” probe alone were lower than observed r values of the “intrinsic” probe, which was well explained in terms of the mode of incorporation of the two types of the probe molecules into the matrix.     

Regional and cultivar comparison of Italian single cultivar olive oils according to flavor profiling

Geographical origin, cultivar, and olive ripening stage are important factors which affect the typical flavor profile of extra virgin olive oils. Aromatic compounds and sensorial profiles of “Casaliva”, “Frantoio”, and “Leccino” olive oils from three different Italian production regions Abruzzo (eastern‐central Italy), Lombardy (northern Italy), and Tuscany (western‐central Italy) were assessed in two cropping years and at three olive ripening stages (green, veraison, and ripe). The chemical aromatic compounds were more effective in discriminating the oils than their sensorial attributes. Oils showed peculiar aromatic and sensorial profiles according to their region of origin. Genetically similar “Casaliva” and “Frantoio” showed also analogous profiles, but distinct from “Leccino”. The interaction between regions of cultivation and cultivars significantly affected the flavor profiling. Practical applications: This research provides a sound proof that geographical origin, cultivar, and fruit ripening stage, could play an important interactive role in shaping the flavor profiling of extra virgin olive oils. This represents a scientific basis of the “typicality” concept, which should address the marketing strategies for exploiting of the PDO products.     

Meaningful evaluation of plastisol gelation and fusion temperatures by dynamic mechanical analysis

In most PVC plastisol processing operations, gelation and fusion characteristics of the plastisol are critically important. For example, in chemically foamed plastisols, plastisol fusion temperature and blowing agent decomposition temperature must be carefully coordinated. In rotomolded parts, rates of gelation may determine the quality of the finished parts. For plastisol products made by any process, the final fusion temperature determines the processing temperatures required to give the finished product acceptable mechanical properties. For a variety of reasons, the methods commonly used to characterize plastisol gelation and fusion (hot bar test, resin in plasticizer clear point, torque rheometer measurements, etc.) provide comparisons between plastisols but do not provide temperatures that are easily related to actual industrial processes. With dynamic mechanical analysis (DMA), one can characterize, under low shear conditions, the temperatures at which gelation begins, gelation ends, and complete fusion occurs. Additionally, it is possible to record plastisol viscosities (and other dynamic mechanical properties) over the processing temperature range. We used a multiple linear regression program to analyze the DMA data for plastisols heated from 30 to 210°C and containing either 70, 80 or 90 phr of Jayflex dihexyl phthalate (DHP) or Jaylflex di-isodecyl phthalate (DIDP). Further, we determined the plasticizer phr dependence and the reproducibility of gel and fusion temperatures given by data analyzed in this manner. Finally, for comparison, we analyzed the reproducibility of initial and final plastisol gel temperatures and fusion temperatures, which were determined by visually analyzing the DMA data for plastisols containing 70, 80, and 90 phr of Jyflex plasticizers DHP, Jayflex 77, diisononyl phthalate (DINP), and DIDP. Precise characterization of plastisol gelation and fusion behavior will, undoubtedly, facilitate substitution of plastisol ingredients as is often required by those who manufacture and process plastisols.     

硫酸-水玻璃体系的成胶特点

研究了用溶胶凝胶和常压干燥的方法制备SiO2气凝胶粉体时，硫酸-水玻璃体系的成胶规律，发现凝胶时间与体系的pH值有较大的关系；在反应物浓度一定的条件下，凝胶时间t-pH曲线成“W”型，随反应物浓度的降低，逐渐向“U”型曲线转变；体系凝胶时间最快点的pH值，在碱性环境中随反应物浓度的减小而降低，在酸性环境中随反应物浓度的减小而增大；这与在碱性和酸性环境中所存在的两种成胶机理有直接的关系。 甲酰胺的引入不会明显改变硫酸-水玻璃体系的成胶特点，但明显改善了SiO2气凝胶的物理性能。     

Effect of plasticizer type on gelation and fusion of PVC plastisol,dialkyl phthalate series

Different grades of PVC resins and a variety of plasticizers are used to adjust processability and properties of plastisol. The plastisol, which is a dispersion of fine particles of PVC in plasticizer, is coated on a substrate and heated in an oven to gel and fuse. In the gelation stage the resin particles become swollen with plasticizer and then, in the fusion stage the entire system fuses to become one homogeneous phase. The finished products are flexible PVC such as coated fabrics and surgical globes. Different plasticizers, because of the difference in solvent power, affect the process of gelation and fusion, and hence, processability. This paper examines such an effect systematically by employing a homologous series of plasticizers, dialkyl phthalates. The progress of gelation and fusion are followed by the measurements of dynamic moduli and by the observation with a scanning electron microscope. As it may be expected, the shorter the alkyl chain, the higher the solvent power of the plasticizer.     

The densification of rigid PVC dry blend during fusion

The mechanism of fusion of suspension PVC rigid dry blend in low-shear processing involves the compaction, densification, intergrain fusion, and elongation of the grains. Using a “zero-length” capillary, the entrance pressure loss was measured for dry blend at various stages of fusion. The initial decrease in the entrance pressure loss curve during processing is related to the fusion of the primary particle agglomerates. The consequences of the entrance pressure loss decrease on the rate of melting during extrusion are discussed.     

Effects of lubricants on the second fusion behavior of rigid polyvinyl chloride

Rigid polyvinyl chloride (RPVC) is thermally unstable and difficult to process. The processibility of RPVC compounds markedly depends on the type and level of lubricants present. Lubricants are compounded into RPVC powder and the resulting dry blend is either directly converted into the final product requiring the resin to fuse only once, or pelletized first followed by conversion into the final product in a subsequent operation requiring the resin to fuse twice. The effects of lubricants on the first fusion have been well studied but little is known about the second fusion. We studied the effects of eleven common lubricants on the second fusion of a RPVC master, batch at three levels of concentration at several temperatures., The lubricants were compunded with the RPVC powder, the dry blends molded into one-inch cube samples, and the molded samples fused under shearing conditions comparable to the actual processing. We found that the effects of the lubricants on the second fusion were generally the same as those on the first fusion. Apparently, the properties of the lubricants and their interactions with the RPVC resin are not altered by the first fusion history.     

Multi-stage fusion regression network for quality prediction of batch process

In most batch processes, the correlations of process variables present multi-stage characteristic as the process progress and operating conditions change. The methods building a local model at each stage ignore the potential correlations among stages, resulting in poor quality prediction of batch process. To solve this problem, a batch process quality prediction method based on multi-stage fusion regression network (MSFRN) is proposed. First, the affine propagation clustering (AP) algorithm is used to automatically divide the stages for batch process without relying on prior knowledge. Second, the input reconstruction error and quality prediction error are organically combined to develop a stacked isomorphic and quality-driven autoencoder (SIQAE) for each stage, which fully extracts the quality-related features for each stage while reducing the input cumulative loss. Then, the self-attention mechanism is used to integrate the quality-related features of each stage so as to obtain global features which consider the correlations among stages. Finally, the global features are input into the fully connected regression layer to predict the quality variables of batch process. The effectiveness of the proposed method was verified by applying on penicillin fermentation process.     

Studies in the process optimization and characterization of low formaldehyde emission urea‐formaldehyde resin by response surface methodology

Stringent control of formaldehyde emission standards the world over has intensified research and development effort to explore several paths for reducing formaldehyde release. A new generation of low odour resins is currently being developed and some resin manufacturers are now programming formaldehyde and urea additions at two or more stages in the overall reaction. This article reports on the studies conducted on a four‐stage condensation process consisting of the first stage involving a high acid environment followed by an alkaline condensation, a condensation under a pH 6, and finally neutralization to pH 7. A programmed variation consisting of changing “the number of additions” and “the duration between additions” of urea to formaldehyde was considered as an effective method to control the molecular weight, molecular weight distribution, and the oligomeric structures. Response surface methodology was employed to optimize the above conditions to produce particle boards with minimum formaldehyde emission and maximum internal bond strength. The studies showed that sequential addition of urea [“the duration between additions” and the “number of additions”] improved the internal bond strength and reduced formaldehyde emission of the particleboards. Detailed resin characterization in terms of the number and weight average molecular weights, molecular weight distribution, polydispersity, percentages of reactive moieties, and interlinking units present in the oligomer could be stipulated. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 2709–2719, 2007     

U‐PVC gelation level assessment,part 1: Comparison of different techniques

Several different gelation assessment methods such as differential scanning calorimetry, capillary rheometry, solvent absorption, wide angle x‐ray scattering, transmission electron microscopy, and atomic force microscopy were applied to a typical PVC window profile formulation subjected to various thermomechanical histories. Shear applied during the process could be decomposed into two components: (i) a thermal component corresponding to the self‐heating that was generated and (ii) a “mechanical” component associated with a “pure” shearing action deprived of any thermal aspect. Shear sensitivity of the above‐mentioned gelation assessment techniques was evaluated by considering both aspects. Gelation levels established by differential scanning calorimetry and capillary rheometry were especially compared, thus allowing a comparison of the two physical aspects evidenced by each technique, i.e., crystallite melting and macromolecular network development. It appeared that as soon as the PVC particulate structure had been fragmented into micronic entities (primary particles) the gelation process was governed mainly by the thermal aspect, i.e., crystallite melting. J. VINYL. ADDIT. TECHNOL. 12:98–107, 2006. © 2006 Society of Plastics Engineers.     

Gelation and fusion profiles of PVC dispersion resins in plastisols

Poly(vinyl chloride) (PVC) plastisols are used for coatings, films, sheets, foams, and rotational castings. In order to satisfy the requirements for the different applications, a variety of PVC dispersion resins are manufactured. The requirements for the plastisols are many: for example, good air release, viscosity stability, fine particle size, foamability, and good heat stability. Processability is another important requirement, which emphasizes the rheological behavior at room temperature and the gelation—fusion behavior. This paper documents research to fingerprint the gelation and fusion profiles of various PVC dispersion resins. The viscoelastic measurements were used to continuously monitor the changes of moduli during gelation and fusion under a heating rate which simulates the temperature profile of the processes. The effects of molecular weight, resin type, and copolymer on the gelation–fusion behavior are discussed.     

A review of the electrofusion joining process for polyethylene pipe systems

Electrofusion joining is now an essential and widely used method to assist in the creation of polyethylene pressure pipe systems. The process of electrofusion joining is reviewed by examining the experimental and some computer simulation literature relating to the temperature and melt pressure changes during the fusion process, and on how varying fusion time and pipe/fitting gap influences the strength of electrofusion joints. From this literature review, four key stages in the joining process are identified. First, an incubation period where the joint has no strength. Second, a joint formation and consolidation stage where an increasing joint temperature aids molecular diffusion to both increase the joint strength and promote a more ductile mode of failure. A plateau region then follows where the joint strength, and ductility, remain reasonably constant despite the fusion time increasing. This plateau is thought to allow some welding variables, such as gap, to have only a small influence on joint strength (for gap maintained within reasonable limits). Finally there is a cooling stage where the joint bridging “tie molecules” become locked into either side of the joint. It is these tie molecules that give the joint its ductility and strength. The concluding section of the review notes some of the important on-site practices that, if followed, allow electrofusion joints to acquire their good strength properties, and hence give polyethylene pressure pipe systems of a high integrity.     

Viscosity and shear modulus of PVC-plastisols during gelation and fusion

The Contraves balance rheometer has been used in a study of the gelation and fusion process of three DOP-based PVC-plastisols and the results compared with those obtained with the Brabender plastograph. The tensile properties of samples fused at different temperatures have also been determined. The rheometer results relate to the temperature dependence of the viscosity, shear modulus, and loss angle of the plastisols used. The viscosity- and modulus-temperature curves are to some extent reminiscent of the torque-temperature curves obtained with the plastograph; the fusion temperatures are slightly different. The loss-angle-temperature curves measured with the rheometer exhibit sharp maxima in the vicinity of the T_g-point of the base polymer. The shear modulus decreases with time when the temperature is kept constant (above the fusion point). This effect is possibly associated with crystallite melting. The temperature necessary to reach the maximum strength plateau of films fused at various temperatures was found to agree (within 10°C) with the maximum in the modulus-temperature curves (minimum in loss-angle-temperature curves) when the rheometer shear rate was sufficiently low. On the whole, the rheometer allows for better temperature control. Also, the fact that the results are given in terms of viscosity and shear modulus may have some advantage in interpreting gelation and fusion data.     

Moldability diagrams for the reaction injection molding of a polyurethane crosslinking system

A trial and error approach reflects the state of the art in reaction injection molding. Material and process parameters determine the “moldability” of a specific system in a particular application. The concept of “molding areas” on the critical parameters plane can be extended form thermoplastic injection molding (TIM) to reaction injection molding (RIM). In this work moldability diagrams for the filling and curing stages of a RIM process are obtained based on a simplified engineering approach. The key process parameters chosen for the filling stage are initial material temperature and filling time. In the curing stage, the critical parameters are considered to be mold wall temperature and demold time. Experimental results obtained on a laboratory-scale RIM machine on a Crosslinking polyurethane system are used to check the validity of the predicted molding areas. The agreement obtained is satisfactory considering the broad range of processing parameters used.