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The coronavirus SARS-CoV-2 causes the severe disease COVID-19. SARS-CoV-2 infection is initiated by interaction of the viral spike protein and host receptor angiotensin-converting enzyme 2 (ACE2). We report an improved bright and reversible fluorogenic reporter, named SURF (split UnaG-based reversible and fluorogenic protein-protein interaction reporter), that we apply to monitor real-time interactions between spike and ACE2 in living cells. SURF has a large dynamic range with a dark-to-bright fluorescence signal that requires no exogenous cofactors. Utilizing this reporter, we carried out a high-throughput screening of small-molecule libraries. We identified three natural compounds that block replication of SARS-CoV-2 in both Vero cells and human primary nasal and bronchial epithelial cells. Cell biological and biochemical experiments validated all three compounds and showed that they block the early stages of viral infection. Two of the inhibitors, bruceine A and gamabufotalin, were also found to block replication of the Delta and Omicron variants of SARS-CoV-2. Both bruceine A and gamabufotalin exhibited potent antiviral activity in K18-hACE2 and wild-type C57BL6/J mice, as evidenced by reduced viral titres in the lung and brain, and protection from alveolar and peribronchial inflammation in the lung, thereby limiting disease progression. We propose that our fluorescent assay can be applied to identify antiviral compounds with potential as therapeutic treatment for COVID-19 and other respiratory diseases.

The kinase ataxia telangiectasia mutated (ATM) plays a key role in the DNA damage response (DDR). It is thus essential to visualize spatiotemporal dynamics of ATM activity during DDR. Here, we designed a robust ATM activity reporter based on phosphorylation-inducible green fluorescent protein phase separation, dubbed ATM–SPARK (separation of phases-based activity reporter of kinase). Upon ATM activation, it undergoes phase separation via multivalent interactions, forming intensely bright droplets. The reporter visualizes spatiotemporal dynamics of endogenous ATM activity in living cells, and its signal is proportional to the amount of DNA damage. ATM-SPARK also enables high-throughput screening of biological and small-molecule regulators. We identified the protein phosphatase 4 that blocks ATM activity. We also identified BGT226 as a potent ATM inhibitor with a median inhibitory concentration of ~3.8 nanomolars. Furthermore, BGT226 sensitizes cancer cells to the radiomimetic drug neocarzinostatin, suggesting that BGT226 might be combined with radiotherapeutic treatment. ATM-SPARK achieves large dynamic range, bright fluorescence, and simple signal pattern.

Dysregulation and enhanced expression of MYC transcription factors including MYC and MYCN contribute to majority of human cancers. For example, MYCN is amplified up to several hundred-fold in high-risk neuroblastoma. One potential consequence of elevated expression is liquid-liquid phase separation (LLPS), occurring when the concentration of certain macromolecules and biopolymers is above a threshold. Here, we show that in MYCN-amplified human neuroblastoma cells, N-myc protein forms condensate-like structures. Using MYCN-nonamplified neuroblastoma cells that have no or little endogenous N-myc protein expression, we found that exogenously expressed N-myc undergoes LLPS in a concentration-dependent manner, and determined its threshold concentration for LLPS in the cellular context. Biophysically, N-myc condensates in live cells exhibit liquid-like behavior. The intrinsically disordered transactivation domain (TAD) of N-myc is indispensable for LLPS. Functionally, the N-myc condensates contain its obligatory DNA-binding and dimerization partner, genomic DNA, transcriptional machinery, and nascent RNA. These condensates are dynamically regulated during cell mitosis, correlated with chromosomal condensation and de-condensation. We further show that the TAD and the DNA-binding domain are both required for transcriptional activity of N-myc condensates. Most importantly, using a chemogenetic tool that decouples the role of phase separation from changes in protein abundance level in the nucleus, we discovered that N-myc phase separation regulates gene transcription and promotes SH-EP cell proliferation. Interestingly, LLPS of N-myc only modulates a small proportion of N-myc-regulated genes. Taken together, our results demonstrate that N-myc undergoes LLPS, and that its phase separation differentially modulates the transcriptome, partially contributes to gene transcription, and promotes cell proliferation. Our work opens a new direction in understanding Myc-related cancer biology that has been studied for several decades.

Claudins (CLs) are membrane proteins found in tight junctions and play a major role in establishing the intercellular barrier. However, some CLs are abnormally overexpressed on tumor cells and are valid clinical biomarkers for cancer diagnosis. Here, we constructed antibody Fab fragment-based Quenchbodies (Q-bodies) as effective and reliable fluorescent sensors for detecting and visualizing CLs on live tumor cells. The variable region genes for anti-CL1 and anti-CL4 antibodies were used to express recombinant Fab fragments, and clones recognizing CL4 with high affinity were selected for making Q-bodies. When two fluorescent dyes were conjugated to the N-terminal tags attached to the Fab, the fluorescent signal was significantly increased after adding nanomolar-levels of purified CL4. Moreover, addition of the Q-body to CL4-expressing cells including CL4-positive cancer cells led to a clear fluorescence signal with low background, even without washing steps. Our findings suggested that such Q-bodies would serve as a potent tool for specifically illuminating membrane targets expressed on cancer cells, both in vitro and in vivo.

Fluorescence-based biosensor probes, especially those based on Förster resonance energy transfer (FRET) between fluorescent protein (FP) variants, are widely used to monitor various biological phenomena, often detecting ligand-induced association of the receptor domains. While antibodies are fertile sources of specific receptors for various biomolecules, their potential has not been fully exploited. In this study, we used a fluorescent probe comprising FP-fused antibody variable region fragments to detect a bone metabolism biomarker, osteocalcin (BGP), by using fluorescence spectrometry/microscopy. Because the association between the two proteins increases in the presence of antigen BGP or its C-terminal peptide, the increased antigen in a sample can be monitored as a FRET efficiency increase, based on the open sandwich fluoroimmunoassay principle. The results clearly indicated that the FP-antibody FRET probe could be used as a diagnostic reagent to measure levels of BGP in the clinically relevant concentration range and to image BGP produced from live osteoblast cells.

Current efforts in the proteolysis targeting chimera (PROTAC) field mostly focus on choosing an appropriate E3 ligase for the target protein, improving the binding affinities towards the target protein and the E3 ligase, and optimizing the PROTAC linker. However, due to the large molecular weights of PROTACs, their cellular uptake remains an issue. Through comparing how different warhead chemistry, reversible noncovalent (RNC), reversible covalent (RC), and irreversible covalent (IRC) binders, affects the degradation of Bruton’s Tyrosine Kinase (BTK), we serendipitously discover that cyano-acrylamide-based reversible covalent chemistry can significantly enhance the intracellular accumulation and target engagement of PROTACs and develop RC-1 as a reversible covalent BTK PROTAC with a high target occupancy as its corresponding kinase inhibitor and effectiveness as a dual functional inhibitor and degrader, a different mechanism-of-action for PROTACs. Importantly, this reversible covalent strategy is generalizable to improve other PROTACs, opening a path to enhance PROTAC efficacy., PROTACs have emerged as promising therapeutic agents but their cellular uptake is often inefficient. Here, the authors show that reversible covalent warhead chemistry improves PROTAC intracellular accumulation and target engagement, and develop a dual inhibitor/degrader of Bruton’s tyrosine kinase

Lipid peroxidation is involved in many disorders and diseases such as cardiovascular disease, cancers, neurodegenerative diseases, and even aging. Lipid peroxidation products existing in blood or bodily fluids are very important biomarkers for the diagnosis of such diseases. In particular, 13(R,S)-hydroxy-9(E),11(E)-octadecadienoic acid (13-(E,E)-HODE) is an oxidiation product of linoleic acid, which is an important biomarker for many diseases such as diabetes and Alzheimer's disease. In this study, we successfully displayed the antigen-binding fragment of an antibody produced by hybridoma 1213-1 on the M13 phage and performed analysis of the antibody variable region genes. The blast results suggested that it is a novel antibody. We also developed a phage-antibody-based competitive ELISA and a novel Open Sandwich ELISA (OS ELISA) for the detection of 13-(E,E)-HODE. The OS ELISA showed a limit of detection (LOD) of 15.6 nM of 13-(E,E)-HODE and low cross-reactivity with other HODE such as 9-(E,E)-HODE. Another format of the open sandwich ELISA with purified maltose binding protein-fused VL and VH-phage showed a lower LOD of 2.2 nM of 13-(E,E)-HODE, which may be sensitive enough to detect the concentration of 13-(E,E)-HODE in patients’ blood samples. This is the first OS ELISA for the detection of lipids, and we believe it also represents the first molecular cloning of anti-HODE antibody genes.

During DNA double-strand break and replication fork repair by homologous recombination, the RAD51 recombinase catalyzes the DNA strand exchange reaction via a helical polymer assembled on single-stranded DNA, termed the presynaptic filament. Our published work has demonstrated a dual function of the SWI5–SFR1 complex in RAD51-mediated DNA strand exchange, namely, by stabilizing the presynaptic filament and maintaining the catalytically active ATP-bound state of the filament via enhancement of ADP release. In this study, we have strived to determine the basis for physical and functional interactions between Mus musculus SWI5–SFR1 and RAD51. We found that SWI5–SFR1 preferentially associates with the oligomeric form of RAD51. Specifically, a C-terminal domain within SWI5 contributes to RAD51 interaction. With specific RAD51 interaction defective mutants of SWI5–SFR1 that we have isolated, we show that the physical interaction is indispensable for the stimulation of the recombinase activity of RAD51. Our results thus help establish the functional relevance of the trimeric RAD51–SWI5–SFR1 complex and provide insights into the mechanistic underpinnings of homology-directed DNA repair in mammalian cells.

Protein-protein interactions (PPIs) mediate signal transduction in cells. Small molecules that regulate PPIs are important tools for biology and biomedicine. Dynamic imaging of small molecule induced PPIs characterizes and verifies these molecules in living cells. It is thus important to develop cellular assays for dynamic visualization of small molecule induced protein-protein association and dissociation in living cells. Here we have applied a fluorophore phase transition based principle and designed a PPI assay named SPPIER (separation of phases-based protein interaction reporter). SPPIER utilizes the green fluorescent protein (GFP) and is thus genetically encoded. Upon small molecule induced PPI, SPPIER rapidly forms highly fluorescent GFP droplets in living cells. SPPIER detects immunomodulatory drug (IMiD) induced PPI between cereblon and the transcription factor Ikaros. It also detects IMiD analogue (e.g., CC-885) induced PPI between cereblon and GSPT1. Furthermore, SPPIER can visualize bifunctional molecules (e.g. PROTAC)-induced PPI between an E3 ubiquitin ligase and a target protein. Lastly, SPPIER can be modified to image small molecule induced protein-protein dissociation, such as nutlin-induced dissociation between HDM2 and p53. The intense brightness and rapid kinetics of SPPIER enable robust and dynamic visualization of PPIs in living cells.

Fluorescence-based probes, especially those that utilize Förster resonance energy transfer (FRET) between fluorescent protein (FP) variants, are widely used to monitor various biological phenomena, most often detecting its ligand-induced conformational change through the receptor domain. While antibody provides a fertile resource of a specific receptor for various biomolecules, its potential has not been fully exploited. An exception is a pair of donor FP-fused VH and acceptor FP-fused VL fragments, which has been proven useful when their association increases in the presence of antigen (open sandwich fluoroimmunoassay, OS-FIA). However, probes for larger proteins such as serum albumin (SA) were difficult to produce, since the interaction between VH and VL of these antibodies is barely affected by the bound antigen. Here, we propose a novel strategy, called open flower fluoroimmunoassay (OF-FIA), using a probe composed of a donor-fused VH and an acceptor-fused VL linked by a disulfide bond between VH and VL (CyPet/YPet-dsFv). The probe gave high FRET efficiency due to the dimerization propensity of the FP pair, while the efficiency got lower as SA concentration increased, probably due to dimer disruption. The constructed probe could detect clinically relevant range of SA, showing its potential as a diagnostic reagent.

Post-translational histone modifications are major regulators of gene expression. However, conventional immunoassays do not provide sufficient information regarding their spatial and temporal dynamic changes. Fluorescence/Förster resonance energy transfer (FRET)-based probes are capable of monitoring the dynamic changes associated with histone modifications in real-time by measuring the balance between histone-modifying enzyme activities. Recently, a genetically encoded histone-modification fluorescent probe using a single-chain variable region (scFv) fragment of a specific antibody was developed. The probe, modification-specific intracellular antibody, is capable of monitoring histone-acetylation levels in both cultured cells and living organisms based on the ratio of fluorescence intensities between the cell nucleus and cytoplasm. In this study, we constructed a FRET probe composed of yellow fluorescent protein attached at the N-terminus of an acetyl H3K9-specific scFv, tethered to a cyan fluorescent protein. When the FRET probe was expressed in human cells, both FRET efficiency and fluorescence intensity in the nucleus increased following histone-deacetylase inhibitor treatment. Using these two parameters, endogenous histone-acetylation levels were quantified over a high dynamic range. This probe provides a simple approach to quantify spatial and temporal dynamic changes in histone acetylation.

Homologous recombination catalyzed by the RAD51 recombinase eliminates deleterious DNA lesions from the genome. In the presence of ATP, RAD51 forms a nucleoprotein filament on single-stranded DNA, termed the presynaptic filament, to initiate homologous recombination-mediated DNA double-strand break repair. The SWI5-SFR1 complex stabilizes the presynaptic filament and enhances its ability to mediate the homologous DNA pairing reaction. Here we characterize the RAD51 presynaptic filament stabilization function of the SWI5-SFR1 complex using optical tweezers. Biochemical experiments reveal that SWI5-SFR1 enhances ATP hydrolysis by single-stranded DNA-bound RAD51. Importantly, we show that SWI5-SFR1 acts by facilitating the release of ADP from the presynaptic filament. Our results thus provide mechanistic understanding of the function of SWI5-SFR1 in RAD51-mediated DNA recombination.

Homologous recombination (HR) represents a major error-free pathway to eliminate pre-carcinogenic chromosomal lesions. The DNA strand invasion reaction in HR is mediated by a helical filament of the Rad51 recombinase assembled on single-stranded DNA that is derived from the nucleolytic processing of the primary lesion. Recent studies have found that the human and mouse Swi5 and Sfr1 proteins form a complex that influences Rad51-mediated HR in cells. Here, we provide biophysical evidence that the mouse Swi5-Sfr1 complex has a 1:1 stoichiometry. Importantly, the Swi5-Sfr1 complex, but neither Swi5 nor Sfr1 alone, physically interacts with Rad51 and stimulates Rad51-mediated homologous DNA pairing. This stimulatory effect stems from the stabilization of the Rad51-ssDNA presynaptic filament. Moreover, we provide evidence that the RSfp (rodent Sfr1 proline rich) motif in Sfr1 serves as a negative regulatory element. These results thus reveal an evolutionarily conserved function in the Swi5-Sfr1 complex and furnish valuable information as to the regulatory role of the RSfp motif that is specific to the mammalian Sfr1 orthologs.

Visualizing dynamics of kinase activity in living animals is essential for mechanistic understanding of cell and developmental biology. We describe GFP-based kinase reporters that phase-separate upon kinase activation via multivalent protein-protein interactions, forming intensively fluorescent droplets. Called SPARK (separation of phases-based activity reporter of kinase), these reporters have large dynamic range (fluorescence change), high brightness, fast kinetics, and are reversible. The SPARK-based protein kinase A (PKA) reporter reveals oscillatory dynamics of PKA activities upon G protein-coupled receptor activation. The SPARK-based extracellular signal-regulated kinase (ERK) reporter unveils transient dynamics of ERK activity during tracheal metamorphosis in live Drosophila. Because of intensive brightness and simple signal pattern, SPARKs allow easy examination of kinase signaling in living animals in a qualitative way. The modular design of SPARK will facilitate development of reporters of other kinases.

The flow of polymer melts through the clearance over a barrier flight in extruders involves high, rapidly changing shear rates. Polymer melts, being viscoelastic, are expected to exhibit a high elasticity when they flow through the clearance, so the flow through the clearance may not be predictable or stable. The flow through the clearance over a barrier flight was investigated using a shear refining (SR) module connected to an extruder. Three polymers with different melt properties were tested: branched low density polyethylene (BLDPE), high-density polyethylene (HDPE), and polystyrene (PS). The measured drag flow rate through the clearance was found to be equal to the prediction for a purely viscous fluid, which gives a linear velocity profile in the clearance. At the threshold rotor speed of the SR module whereupon the predicted drag flow rate through the clearance is the same as the extruder output rate, the melt pressures at the inlet and the outlet of the SR module were nearly equal and stable. Below the threshold rotor speed, the inlet pressure was higher than the outlet pressure. Above the threshold rotor speed, the inlet pressure was nearly zero and the outlet pressure fluctuated. The magnitude of the pressure fluctuation increased with increasing rotor speed and decreased with increasing melt temperature. HDPE, which had a higher melt elasticity, showed more pressure fluctuation than BLDPE and PS. The pressure fluctuation probably results from the flow instability through the clearance caused by the melt elasticity.

Screw design technology is considered to be empirical and secretive. The production rate of single-screw extruders is often limited by the melting capacity. The melting capacity of a screw depends on the polymer properties, the processing conditions and the particular geometry of the screw. Once the melting capacity is predicted, the screw can be designed to match the melting capacity. This paper presents a scientific approach to screw design based on an analytical melting model, with an example.

Background Human interactome is predicted to contain 150,000 to 300,000 protein-protein interactions, (PPIs). Protein-fragment complementation assay (PCA) is one of the most widely used methods to detect PPI, as well as Förster resonance energy transfer (FRET). To date, successful applications of firefly luciferase (Fluc)-based PCA have been reported in vivo, in cultured cells and in cell-free lysate, owing to its high sensitivity, high signal-to-background (S/B) ratio, and reversible response. Here we show the assay also works with purified proteins with unexpectedly rapid kinetics. Results Split Fluc fragments both fused with a rapamycin-dependently interacting protein pair were made and expressed in E. coli system, and purified to homogeneity. When the proteins were used for PCA to detect rapamycin-dependent PPI, they enabled a rapid detection (~1 s) of PPI with high S/B ratio. When Fn7-8 domains (7 nm in length) that was shown to abrogate GFP mutant-based FRET was inserted between split Fluc and FKBP12 as a rigid linker, it still showed some response, suggesting less limitation in interacting partner’s size. Finally, the stability of the probe was investigated. Preincubation of the probes at 37 degreeC up to 1 h showed marked decrease of the luminescent signal to 1.5%, showing the limited stability of this system. Conclusion Fluc PCA using purified components will enable a rapid and handy detection of PPIs with high S/B ratio, avoiding the effects of concomitant components. Although the system might not be suitable for large-scale screening due to its limited stability, it can detect an interaction over larger distance than by FRET. This would be the first demonstration of Fluc PCA in vitro, which has a distinct advantage over other PPI assays. Our system enables detection of direct PPIs without risk of perturbation by PPI mediators in the complex cellular milieu.

Various types of polyethylene homopolymers and copolymers, including linear high-density polyethylene (HDPE), branched low-density polyethylene (BLDPE), poly(ethylene vinyl acetate) copolymer (EVA), heterogeneous linear poly(ethylene/α-olefin) copolymer (het-LEAO) or commonly known as linear low-density polyethylene, homogeneous linear poly(ethylene/α-olefin) copolymer (hom-LEAO), and homogeneous branched poly(ethylene/α-olefin) copolymer (hom-BEAO), were evaluated for their melt rheological and thermodynamic properties with emphasis on their molecular structure. Short-chain branching (SCB) mainly controls the density, but it has little effect on the melt rheological properties. Long-chain branching (LCB) has little effect on the density and thermodynamic properties, but it has drastic effects on the melt rheological properties. LCB increases the pseudo-plasticity and the flow activation energy for both the polyethylene homopolymer and copolymer. Compared at a same melt index and a similar density, hom-LEAO has the highest viscosity in processing among all polymers due to its linear molecular structure and very narrow molecular weight distribution. Small amounts of LCB in hom-BEAO very effectively reduce the average viscosity and also improve the flow stability. Both hom-LEAO and hom-BEAO, unlike het-LEAO, have thermodynamic properties similar to BLDPE. © 1996 John Wiley & Sons, Inc.

This paper presents an unmanned underwater vehicle (UUV) with high maneuverability to be controlled in strong tidal currents. A radio buoy is connected to the UUV with an intermediate cable, and a wireless RF modem is installed to communicate with a support vessel. This paper presents the design and development of the UUV and the buoy systems. The vehicle equips with two main thrusters and four vertical/ horizontal tunnel thrusters in the middle of the vehicle. This paper discusses the hydrodynamic characteristics of the multiple thrusters, and strategies to maneuver the UUV with multiple thruster. Finally this paper presents effectiveness of the UUV with the buoy in conducting a simulated object installation.

Solid state friction reduction has been found to be an effective method for extrusion stabilization of a high coefficient of friction (COF) thermally sensitive polymer. A poly(vinylidenechloride) copolymer (PVDC) was studied alone and blended with various polyolefins to change its frictional behavior. COF of the polymer rubbing on a metal surface was measured under conditions typical of an extrusion process. These results correlated well with the measured mechanical energy consumed during extrusion. Of the polyolefins studied, high and low density polyethylene were found to be very effective for lowering friction and improving extrusion performance of the PVDC. Polypropylene was found to be much less effective. Interface temperature where melting occurs due to frictionally generated heat has been experimentally shown to be a function of COF and the bulk metal temperature.

A study of melting a polymer pellet immersed in a hot silicone oil bath was conducted. The temperature rise at the center of the pellet was recorded. This experiment simulates the conduction melting mechanism of polymer solid pieces mixed in the hot melt inside an extruder screw channel. The pellets immersed in the silicone oil melted quite slowly, taking around one minute to melt a spherical pellet of about 4.5 mm diameter. The heating time could be greatly decreased by stirring the silicone oil to increase the heat transfer from the silicone oil to the pellet. Analysis of the conduction melting mechanism showed that the size reduction of the solid would be most effective in decreasing the heating time.

The frictional behavior of 12 polyethylene samples with densities ranging from 0.963 down to 0.870 g/cc on a metal surface was studied. The samples with densities higher than 0.908 g/cc behaved as rigid plastics, sliding on the metal surface. The samples with densities lower than 0.905 g/cc behaved as elastomers, strongly adhering on the metal surface and tearing within the polymer. Melting occurred when the metal was heated to a temperature above the melting range of the sample. The frictional behavior of a polyethylene can be understood in terms of the density and melting temperature range of the sample.

Our laboratory recently published several analytical equations that can be used to predict the melting rate of fully compacted solid polymers sliding on a heated metal surface, modeling the melting mechanism inside an extruder. These equations were obtained by seeking asymptotic solutions to the differential equations describing the melting mechanism, temperature, and shear-dependent viscosity of polymer melts. Following the same asymptotic approach, we successfully developed accompanying analytical equations for predicting the stress required to slide fully compacted solid polymers on a heated metal surface. The accuracy of these analytical stress equations was found to be reasonable, although not fully satisfactory, by comparing their predictions to the experimentally measured values. The accuracy of the stress calculation is directly related to the accuracy of the viscosity values at high shear rates. The consideration of the temperature and shear dependencies of melt viscosity is most important for accurate prediction of the stress, just as it is for the melting rate. The stress not only depends on the melt rheological properties of the polymer but also on the thermodynamic properties.

Prediction of the screw horsepower requirement involves, among many others, the calculation of the shear stress (τs) between the solid polymer and the barrel surface during melting. Prediction of the solid bed down-channel velocity also requires the calculation of τs. However, the pseudoplastic nature and strong temperature dependence of melt viscosity make the mathematics of calculating τs extremely difficult. As a first step of developing a reasonable mathematical model for calculating τs, experimental measurements of τs were made over a wide range of metal temperature and sliding speed for five commercial polymers using molded, block samples. Although dependences of τs on metal temperature and sliding speed were found to have similar functionality to those of the dependences of melt viscosity on melt temperature and shear rate, this study showed that τs could not be expressed as a sole function of the melt rheological properties. Our subsequent study, to be reported in a follow up paper, will show that τs must be expressed as a function of the thermodynamic properties and melt density of the polymer as well as the melt rheological properties and the melting conditions.

Our laboratory previously reported the observation of a high temperature, melt rheological transition in a styrene–butadiene–styrene (S:7 × 103 and B:43 × 103) block copolymer from the highly elastic, nonlinear viscous behavior typical of a multiphase structure to linear viscous behavior with insignificant elasticity typical of a single-phase structure. We have investigated the precise nature of this melt rheological transition in the 7S-43B-7S sample by measuring the dynamic viscoelastic properties at more than 11 temperatures, including several in the transition region. A new procedure was developed for accurately measuring the sample temperature in a Weissenberg rheogoniometer. The transition is found to start at about 140°C and proceed over a narrow transition region from 140 to about 150°C. Data at all temperatures superimpose onto a single master curve only at high reduced frequencies. At low reduced frequencies, two characteristic branches of the master curve are formed. The data at temperatures below the transition region superimpose onto the upper branch where the dynamic viscosity η′(ω) is a strong function of ω, whereas the data at temperatures above the transition region superimpose onto the lower branch where η′(ω) is independent of ω. The data at temperatures within the transition region fall between the upper and lower branches, ordered according to their temperature positions. The apparent flow activation energy is found to be constant at about 22.8 kcal/mole below the transition region, but appears to decrease to about 17.4 kcal/mole above the transition region. The narrowness of the rheological transition far above the glass transition temperature of the polystyrene domains and the limiting linear viscoelastic behavior at low frequencies above the transition suggest an accompanying morphological transition rather than a gradual weakening of the polystyrene domains.

In the most commonly used scale-up method of plasticating extruder screws, the screw channel depth is increased by the square root of the diameter ratio while the screw RPM is decreased by the square root of the diameter ratio such that the output rate increases proportionally to the square of the diameter ratio. This scale-up method, largely based on the pumping function of the screw, often leads to a higher melt temperature, a higher screw horsepower consumption per unit output rate and an inferior melt quality from the larger diameter screw. Analysis of the common scale-up method reveals that, although the shear rate in the melt is kept constant, the average residence time and the peripheral screw speed are increased for the larger diameter screw. Our recent study on the melting mechanism also reveals that the melting capacity increases less than the pumping capacity. A detailed examination of the common scale-up method in this paper shows that the pumping capacity and the solid conveying capacity increase more than necessary while the melting capacity increases insufficiently.

There are two distinct solid conveying theories that can be applied to plasticating screw extruders. One is Darnell and Mol's theory based on a solid-to-solid friction model and the other is Chung's theory based on a viscous shearing model. The two theories predict very different solid conveying performances for a same set of conditions. In this paper, the maximum pressures that can be developed inside plasticating screw extruders by the solid conveying force are calculated using each of the two theories. Comparison of the results may shed some light on the applicability of each theory for a particular extrusion operation.

Polymer processing consists of basically three functional steps: plasticization of a solid polymer, forming of the plasticized polymer into a desired shape, and solidification of the formed polymer. Polymer processing requires a good knowledge in the melt rheology, morphology, mechanochemistry, melting and crystallization behavior of the polymer as well as engineering knowledge in heating, cooling and deformation processes. Thus, it presents an unusual challenge to polymer engineers and scientists. The gap between theory and practice is extremely large in polymer processing. In spite of extensive fundamental knowledge, many problems in the procedure still remains “practically” unsolved. In this paper, three important examples of the unsolved problems in polymer processing—namely, screw extrusion process, weld-line (self-diffusion) behavior of polymer melt, and temperature build-up in capillary flow—are discussed in detail.

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.

Many polymers suffer from excessive heat generation during processing due to high viscosity, and reduction of viscosity is desired to control the melt temperature during processing. The concept of solid solvent was recently proposed based on thermally reversible compatibility between a polymer-additive pair. Benzenesulfonamide was found to be virtually a perfect solid solvent for polystyrene, and this finding clearly proves that solid solvents can be used as processing aid for polymers to effectively reduce the viscosity.