Psychophysics and neuronal bases of sound localization in humans

Localization of sound sources is a considerable computational challenge for the human brain. Whereas the visual system can process basic spatial information in parallel, the auditory system lacks a straightforward correspondence between external spatial locations and sensory receptive fields. Consequently, the question how different acoustic features supporting spatial hearing are represented in the central nervous system is still open. Functional neuroimaging studies in humans have provided evidence for a posterior auditory "where" pathway that encompasses non-primary auditory cortex areas, including the planum temporale (PT) and posterior superior temporal gyrus (STG), which are strongly activated by horizontal sound direction changes, distance changes, and movement. However, these areas are also activated by a wide variety of other stimulus features, posing a challenge for the interpretation that the underlying areas are purely spatial. This review discusses behavioral and neuroimaging studies on sound localization, and some of the competing models of representation of auditory space in humans. This article is part of a Special Issue entitled Human Auditory Neuroimaging.

Using neuroimaging to understand the cortical mechanisms of auditory selective attention

Over the last four decades, a range of different neuroimaging tools have been used to study human auditory attention, spanning from classic event-related potential studies using electroencephalography to modern multimodal imaging approaches (e.g., combining anatomical information based on magnetic resonance imaging with magneto- and electroencephalography). This review begins by exploring the different strengths and limitations inherent to different neuroimaging methods, and then outlines some common behavioral paradigms that have been adopted to study auditory attention. We argue that in order to design a neuroimaging experiment that produces interpretable, unambiguous results, the experimenter must not only have a deep appreciation of the imaging technique employed, but also a sophisticated understanding of perception and behavior. Only with the proper caveats in mind can one begin to infer how the cortex supports a human in solving the "cocktail party" problem. This article is part of a Special Issue entitled Human Auditory Neuroimaging.

Exposure to air pollution near a steel plant and effects on cardiovascular physiology: a randomized crossover study

BACKGROUND

Iron and steel industry is an important source of air pollution emissions. Few studies have investigated cardiovascular effects of air pollutants emitted from steel plants.

OBJECTIVE

We examined the influence of outdoor air pollution in the vicinity of a steel plant on cardiovascular physiology in Sault Ste. Marie, Canada.

METHODS

Sixty-one healthy, non-smoking subjects (females/males=33/28, median age 22 years) spent 5 consecutive 8-hour days outdoors in a residential area neighbouring a steel plant, or on a college campus approximately 5 kilometres away from the plant, and then crossed over to the other site with a 9-day washout. Mid day, subjects underwent daily 30-minute moderate intensity exercise. Blood pressure (BP) and pulse rate were determined daily and post exercise at both sites. Flow-mediated vasodilation (FMD) was determined at the site near the plant. Air pollution was monitored at both sites. Mixed-effects regressions were run for statistical associations, adjusting for weather variables.

RESULTS

Concentrations of ultrafine particles, sulphur dioxide (SO2), nitrogen dioxide (NO2) and carbon monoxide (CO) were 50-100% higher at the site near the plant than at the college site, with minor differences in temperature, humidity, and concentrations of particulate matter ≤2.5 μm in size (PM2.5) and ozone (O3). Resting pulse rate [mean (95% confidence interval)] was moderately higher near the steel plant [+1.53 bpm (0.31, 2.78)] than at the college site, male subjects having the highest pulse rate elevation [+2.77 bpm (0.78, 4.76)]. Resting systolic and diastolic BP and pulse pressure, and post-exercise BP and pulse rate were not significantly different between two sites. Interquartile range concentrations of SO2 (2.9 ppb), NO2 (5.0 ppb) and CO (0.2 ppm) were associated with increased pulse rate [0.19 bpm (-0.00, 0.38), 0.86 bpm (0.03, 1.68), and 0.11 bpm (0.00, 0.22), respectively], ultrafine particles (10,256 count/cm(3)) associated with increased pulse pressure [0.85 mmHg (0.23, 1.48)], and NO2 and CO inversely associated with FMD [-0.14% (-0.31, 0.02), -0.02% (-0.03, -0.00), respectively]. SO2 during exercise was associated with increased pulse rate [0.26 bpm (0.01, 0.51)].

CONCLUSION

Air quality in residential areas near steel plants may influence cardiovascular physiology.

Echo-Doppler assessment of arterial stiffness in pediatric patients with Kawasaki disease

BACKGROUND

There is growing evidence to suggest increased arterial stiffness in patients with a history of Kawasaki disease (KD). Pulse-wave velocity (PWV) is the most validated measure of arterial stiffness. The aim of this study was to determine if aortic PWV is increased in children with KD.

METHODS

This was a retrospective cohort study. The study cohort was composed of 42 patients with KD (mean age, 9.7 ± 2.0 years) and 44 age-matched control subjects. The primary measure was aortic PWV. Secondary measures included characteristic impedance (Zc), input impedance (Zi), elastic pressure-strain modulus (Ep), and β stiffness index and the following measures of left ventricular size and function: end-diastolic and end-systolic dimensions, wall thickness in diastole and systole, mass, shortening and ejection fractions, mean velocity of circumferential fiber shortening, and stress at peak systole. The appropriate measures were indexed to body surface area. The aortic stiffness and impedance indexes were derived using an echocardiography-Doppler method.

RESULTS

Height, weight, body mass index, and body surface area were similar between the groups. PWV was higher in patients with KD compared with controls (495 vs 370 cm/sec, P = .0008). Zc, Ep, and β stiffness index were higher in patients with KD, but the difference was not statistically significant. Left ventricular dimensions were all within normal limits, with no differences between the groups. Patients with KD had lower stress at peak systole compared with controls (55 vs 64 g/cm(2), P = .01). There was a significant association between the length of time between the initial diagnosis and testing with PWV (r = 0.32, P = .04) and Zi (r = -0.38, P = .01) in patients with KD. There was no significant association between the arterial stiffness indexes (PWV, Zi, Zc, Ep, and β stiffness index) and length of fever, age at KD diagnosis, or heart rate. Logistic regression analysis revealed no association between coronary artery lesion classification and length of fever, day of illness at first treatment, age at KD diagnosis, or any of the arterial stiffness indexes. In the control group, there were significant associations between age and heart rate (r = -0.48, P = .001), Zi (r = -0.55, P < .0001), Zc (r = -0.66, P < .0001), and β stiffness index (r = -0.31, P = .04). There was an association between heart rate and Zc (r = 0.44, P = .003) but no association between heart rate and PWV, Zi, Ep, or β stiffness index.

CONCLUSIONS

Arterial stiffness was increased in children with KD. There was no association between acute-phase KD coronary involvement and PWV. This implies that patients with KD may be at increased cardiovascular risk in the future.

Elongation of textile pelvic floor implants under load is related to complete loss of effective porosity, thereby favoring incorporation in scar plates

Use of textile structures for reinforcement of pelvic floor structures has to consider mechanical forces to the implant, which are quite different to the tension free conditions of the abdominal wall. Thus, biomechanical analysis of textile devices has to include the impact of strain on stretchability and effective porosity. Prolift(®) and Prolift + M(®), developed for tension free conditions, were tested by measuring stretchability and effective porosity applying mechanical strain. For comparison, we used Dynamesh-PR4(®), which was designed for pelvic floor repair to withstand mechanical strain. Prolift(®) at rest showed moderate porosity with little stretchability but complete loss of effective porosity at strain of 4.9 N/cm. Prolift + M(®) revealed an increased porosity at rest, but at strain showed high stretchability, with subsequent loss of effective porosity at strain of 2.5 N/cm. Dynamesh PR4(®) preserved its high porosity even under strain, but as consequence of limited stretchability. Though in tension free conditions Prolift(®) and Prolift + M(®) can be considered as large pore class I meshes, application of mechanical strain rapidly lead to collapse of pores. The loss of porosity at mechanical stress can be prevented by constructions with high structural stability. Assessment of porosity under strain was found helpful to define requirements for pelvic floor devices. Clinical studies have to prove whether devices with high porosity as well as high structural stability can improve the patients' outcome.

Phycocyanobilin promotes PC12 cell survival and modulates immune and inflammatory genes and oxidative stress markers in acute cerebral hypoperfusion in rats

Since the inflammatory response and oxidative stress are involved in the stroke cascade, we evaluated here the effects of Phycocyanobilin (PCB, the C-Phycocyanin linked tetrapyrrole) on PC12 cell survival, the gene expression and the oxidative status of hypoperfused rat brain. After the permanent bilateral common carotid arteries occlusion (BCCAo), the animals were treated with saline or PCB, taking samples 24h post-surgery. Global gene expression was analyzed with GeneChip Rat Gene ST 1.1 from Affymetrix; the expression of particular genes was assessed by the Fast SYBR Green RT-PCR Master Mix and Bioplex methods; and redox markers (MDA, PP, CAT, SOD) were evaluated spectrophotometrically. The PCB treatment prevented the H2O2 and glutamate induced PC12 cell injury assessed by the MTT assay, and modulated 190 genes (93 up- and 97 down-regulated) associated to several immunological and inflammatory processes in BCCAo rats. Furthermore, PCB positively modulated 19 genes mostly related to a detrimental pro-inflammatory environment and counteracted the oxidative imbalance in the treated BCCAo animals. Our results support the view of an effective influence of PCB on major inflammatory mediators in acute cerebral hypoperfusion. These results suggest that PCB has a potential to be a treatment for ischemic stroke for which further studies are needed.

Ascending monoaminergic systems alterations in Alzheimer's disease. translating basic science into clinical care

Extensive neuropathological studies have established a compelling link between abnormalities in structure and function of subcortical monoaminergic (MA-ergic) systems and the pathophysiology of Alzheimer's disease (AD). The main cell populations of these systems including the locus coeruleus, the raphe nuclei, and the tuberomamillary nucleus undergo significant degeneration in AD, thereby depriving the hippocampal and cortical neurons from their critical modulatory influence. These studies have been complemented by genome wide association studies linking polymorphisms in key genes involved in the MA-ergic systems and particular behavioral abnormalities in AD. Importantly, several recent studies have shown that improvement of the MA-ergic systems can both restore cognitive function and reduce AD-related pathology in animal models of neurodegeneration. This review aims to explore the link between abnormalities in the MA-ergic systems and AD symptomatology as well as the therapeutic strategies targeting these systems. Furthermore, we will examine possible mechanisms behind basic vulnerability of MA-ergic neurons in AD.

Food-intake dysregulation in type 2 diabetic Goto-Kakizaki rats: hypothesized role of dysfunctional brainstem thyrotropin-releasing hormone and impaired vagal output

Thyrotropin-releasing hormone (TRH), a neuropeptide contained in neural terminals innervating brainstem vagal motor neurons, enhances vagal outflow to modify multisystemic visceral functions and food intake. Type 2 diabetes (T2D) and obesity are accompanied by impaired vagal functioning. We examined the possibility that impaired brainstem TRH action may contribute to the vagal dysregulation of food intake in Goto-Kakizaki (GK) rats, a T2D model with hyperglycemia and impaired central vagal activation by TRH. Food intake induced by intracisternal injection of TRH analog was reduced significantly by 50% in GK rats, compared to Wistar rats. Similarly, natural food intake in the dark phase or food intake after an overnight fast was reduced by 56-81% in GK rats. Fasting (48h) and refeeding (2h)-associated changes in serum ghrelin, insulin, peptide YY, pancreatic polypeptide and leptin, and the concomitant changes in orexigenic or anorexigenic peptide expression in the brainstem and hypothalamus, all apparent in Wistar rats, were absent or markedly reduced in GK rats, with hormone release stimulated by vagal activation, such as ghrelin and pancreatic polypeptide, decreased substantially. Fasting-induced Fos expression accompanying endogenous brainstem TRH action decreased by 66% and 91%, respectively, in the nucleus tractus solitarius (NTS) and the dorsal motor nucleus of the vagus (DMV) in GK rats, compared to Wistar rats. Refeeding abolished fasting-induced Fos-expression in the NTS, while that in the DMV remained in Wistar but not GK rats. These findings indicate that dysfunctional brainstem TRH-elicited vagal impairment contributes to the disturbed food intake in T2D GK rats, and may provide a pathophysiological mechanism which prevents further weight gain in T2D and obesity.

Effects of dietary fatty acid composition from a high fat meal on satiety

The composition of fats within a high-fat (HF) meal may differentially affect hunger and satiety.

PURPOSE

Compare HF meals rich in either monounsaturated fatty acids (MUFAs), polyunsaturated fatty acids (PUFAs), or saturated fatty acids (SFAs) on the satiety hormone, peptide YY (PYY), and subjective feelings of hunger and fullness.

METHODS

Fifteen normal weight women (18-45 year) were randomized in a crossover design to complete three study visits. The three treatments (three visits) were HF meals (70% of energy from fat) rich in MUFAs (42% of total energy), PUFAs (42% of total energy), or SFAs (45% of total energy). At each visit, subjects consumed a HF meal and eight blood draws were collected over a 5 h period. A visual analog scale (VAS) was completed at the same time as each blood draw for subjective feelings of hunger and fullness.

RESULTS

The postprandial PYY response (area under the curve) was significantly lower (p<0.05) for the MUFA-rich meal (MUFA: 534.5±27.2 pg/mL/5 h) vs. the SFA-rich or PUFA-rich meals (SFA: 607.3±51.6 pg/mL/5h, PUFA: 633.1±35.8 pg/mL/5 h). The SFA-rich meal elicited greater subjective feelings of fullness compared to MUFA- and PUFA-rich meals (288.1±9.6 vs. 236.8±7.9 and 220.9±7.4 mm/5 h; p=0.04, for 5h AUC for SFA, MUFA, and PUFA, respectively). The only significant correlations between PYY levels and VAS measures were found with the SFA-rich meal.

CONCLUSION

Our data shows that liquid meals rich in MUFAs may elicit a weaker satiety response based on PYY levels compared to liquid meals rich in PUFAs or SFAs in normal weight women.

Surface plasmon resonance spectroscopy for characterisation of membrane protein-ligand interactions and its potential for drug discovery

Surface plasmon resonance (SPR) spectroscopy is a rapidly developing technique for the study of ligand binding interactions with membrane proteins, which are the major molecular targets for validated drugs and for current and foreseeable drug discovery. SPR is label-free and capable of measuring real-time quantitative binding affinities and kinetics for membrane proteins interacting with ligand molecules using relatively small quantities of materials and has potential to be medium-throughput. The conventional SPR technique requires one binding component to be immobilised on a sensor chip whilst the other binding component in solution is flowed over the sensor surface; a binding interaction is detected using an optical method that measures small changes in refractive index at the sensor surface. This review first describes the basic SPR experiment and the challenges that have to be considered for performing SPR experiments that measure membrane protein-ligand binding interactions, most importantly having the membrane protein in a lipid or detergent environment that retains its native structure and activity. It then describes a wide-range of membrane protein systems for which ligand binding interactions have been characterised using SPR, including the major drug targets G protein-coupled receptors, and how challenges have been overcome for achieving this. Finally it describes some recent advances in SPR-based technology and future potential of the technique to screen ligand binding in the discovery of drugs. This article is part of a Special Issue entitled: Structural and biophysical characterisation of membrane protein-ligand binding.

Screening of synthetic PDE-5 inhibitors and their analogues as adulterants: analytical techniques and challenges

The popularity of phosphodiesterase type 5 (PDE-5) enzyme inhibitors for the treatment of erectile dysfunction has led to the increase in prevalence of illicit sexual performance enhancement products. PDE-5 inhibitors, namely sildenafil, tadalafil and vardenafil, and their unapproved designer analogues are being increasingly used as adulterants in the herbal products and health supplements marketed for sexual performance enhancement. To date, more than 50 unapproved analogues of prescription PDE-5 inhibitors were found as adulterants in the literature. To avoid detection of such adulteration by standard screening protocols, the perpetrators of such illegal products are investing time and resources to synthesize exotic analogues and devise novel means for adulteration. A comprehensive review of conventional and advance analytical techniques to detect and characterize the adulterants is presented. The rapid identification and structural elucidation of unknown analogues as adulterants is greatly enhanced by the wide myriad of analytical techniques employed, including high performance liquid chromatography (HPLC), gas chromatography-mass spectrometry (GC-MS), liquid chromatography mass-spectrometry (LC-MS), nuclear magnetic resonance (NMR) spectroscopy, vibrational spectroscopy, liquid chromatography-Fourier transform ion cyclotron resonance-mass spectrometry (LC-FT-ICR-MS), liquid chromatograph-hybrid triple quadrupole linear ion trap mass spectrometer with information dependent acquisition, ultra high performance liquid chromatography-time of flight-mass spectrometry (UHPLC-TOF-MS), ion mobility spectroscopy (IMS) and immunoassay methods. The many challenges in detecting and characterizing such adulterants, and the need for concerted effort to curb adulteration in order to safe guard public safety and interest are discussed.

The methionine precursor DL-2-hydroxy-(4-methylthio)butanoic acid protects intestinal epithelial barrier function

DL-2-hydroxy-(4-methylthio)butanoic acid (HMTBA) is a source of dietary methionine (Met) that is widely used in poultry nutrition. We have previously shown that HMTBA is preferentially diverted to the transsulfuration pathway, which gives antioxidant metabolites such as taurine and glutathione. Therefore, here we hypothesize that this Met source can protect epithelial barrier function in an in vitro model of intestinal inflammation of Caco-2 cells. The results show that HMTBA prevents the increase in paracellular permeability induced by H2O2 or tumour necrosis factor-α. This effect can be attributed to the increased production of taurine and reduced glutathione. Similar results were obtained for DL-Met, although the protective role of the amino acid was less pronounced than that of the hydroxy analogue. In conclusion, the diversion to the transsulfuration pathway means that this Met precursor is of greater value than previously thought, due to its capacity to improve intestinal homeostasis and the quality of poultry products destined for human consumption.

Optimizing reconstruction of oncologic sternectomy defects based on surgical outcomes

BACKGROUND

The optimal strategy for oncologic sternectomy reconstruction has not been well characterized. We hypothesized that the major factors driving the reconstructive strategy for oncologic sternectomy include the need for skin replacement, extent of the bony sternectomy defect, and status of the internal mammary vessels.

STUDY DESIGN

We reviewed consecutive oncologic sternectomy reconstructions performed at The University of Texas MD Anderson Cancer Center during a 10-year period. Regression models analyzed associations between patient, defect, and treatment factors and outcomes to identify patient and treatment selection criteria. We developed a generalized management algorithm based on these data.

RESULTS

Forty-nine consecutive patients underwent oncologic sternectomy reconstruction (mean follow-up 18 ± 23 months). More sternectomies were partial (74%) rather than total/subtotal (26%). Most defects (n = 40 [82%]) required skeletal reconstruction. Pectoralis muscle flaps were most commonly used for sternectomies with intact overlying skin (64%) and infrequently used when a presternal skin defect was present (36%; p = 0.06). Free flaps were more often used for total/subtotal vs partial sternectomy defects (75% vs 25%, respectively; p = 0.02). Complication rates for total/subtotal sternectomy and partial sternectomy were equivalent (46% vs 44%, respectively; p = 0.92).

CONCLUSIONS

Despite more extensive sternal resections, total/subtotal sternectomies resulted in equivalent postoperative complications when combined with the appropriate soft-tissue reconstruction. Good surgical and oncologic outcomes can be achieved with defect-characteristic-matched reconstructive strategies for these complex oncologic sternectomy resections.

Magnetophysiologic and echocardiographic comparison of blocked atrial bigeminy and 2:1 atrioventricular block in the fetus

BACKGROUND

Blocked atrial bigeminy (BAB) and second-degree atrioventricular block with 2:1 conduction block (2:1 AVB) both present as ventricular bradycardia and can be difficult to distinguish by echocardiography. Since the prognosis and clinical management of these rhythms are different, an accurate diagnosis is essential.

OBJECTIVE

To identify magnetic and mechanical heart rate and rhythm parameters that could reliably distinguish BAB from 2:1 AVB.

METHODS

A retrospective study of ten BAB and seven 2:1 AVB subjects was performed, using fMCG and pulsed Doppler ultrasound.

RESULTS

Distinguishing BAB from 2:1 AVB by using fMCG was relatively straightforward because in BAB the ectopic P wave (P') occurred early, resulting in a bigeminal (short-long) atrial rhythm. The normalized coupling interval of the ectopic beat (PP' of the blocked beat to PP of the conducted beat) was 0.29 ± 0.03. In contrast, the echocardiographic assessment of inflow-outflow gave a normalized mechanical coupling interval (AA'/AA) near 0.5, which made it difficult to distinguish BAB from 2:1 AVB. Heart rate distinguished most subjects with BAB from those with 2:1 AVB (82 ± 5.7 beats/min vs 69 ± 4.2 beats/min), but was not a completely reliable indicator. In most subjects, BAB alternated with sinus rhythm or other rhythms, resulting in complex heart rate and rhythm patterns.

CONCLUSIONS

Fetal BAB and 2:1 AV block can be difficult to distinguish using echocardiography because in many fetuses with BAB the mechanical rhythm does not accurately reflect the magnetic rhythm. fMCG provides a more reliable means of making a differential diagnosis.

A myriad of functions and complex regulation of the CCR7/CCL19/CCL21 chemokine axis in the adaptive immune system

The chemokine receptor CCR7 and its ligands CCL19 and CCL21 control a diverse array of migratory events in adaptive immune function. Most prominently, CCR7 promotes homing of T cells and DCs to T cell areas of lymphoid tissues where T cell priming occurs. However, CCR7 and its ligands also contribute to a multitude of adaptive immune functions including thymocyte development, secondary lymphoid organogenesis, high affinity antibody responses, regulatory and memory T cell function, and lymphocyte egress from tissues. In this survey, we summarise the role of CCR7 in adaptive immunity and describe recent progress in understanding how this axis is regulated. In particular we highlight CCX-CKR, which scavenges both CCR7 ligands, and discuss its emerging significance in the immune system.

A novel peptide nanomedicine for treatment of pancreatogenic diabetes

Pancreatogenic diabetes (PD) is a potentially fatal disease that occurs secondary to pancreatic disorders. The current anti-diabetic therapy for PD is fraught with adverse effects that can increase morbidity. Here we investigated the efficacy of novel peptide nanomedicine: pancreatic polypeptide (PP) in sterically stabilized micelles (SSM) for management of PD. PP exhibits significant anti-diabetic efficacy but its short plasma half-life curtails its therapeutic application. To prolong and improve activity of PP in vivo, we evaluated the delivery of PP in SSM. PP-SSM administered to rats with PD, significantly improved glucose tolerance, insulin sensitivity and hepatic glycogen content compared to peptide in buffer. The studies established the importance of micellar nanocarriers in protecting enzyme-labile peptides in vivo and delivering them to target site, thereby enhancing their therapeutic efficacy. In summary, this study demonstrated that PP-SSM is a promising novel anti-diabetic nanomedicine and therefore should be further developed for management of PD.

FROM THE CLINICAL EDITOR

Pancreatic peptide was earlier demonstrated to address pancreatogenic diabetes, but its short half-life represented major difficulties in further development for therapeutic use. PP-SSM (pancreatic polypeptide in sterically stabilized micelles) is a promising novel anti-diabetic nanomedicine that enables prolonged half-life and increased bioactivity of PP, as shown in this novel study, paving the way toward clinical studies in the near future.

Pulsatile haemodynamic parameters are predictors of survival in paediatric pulmonary arterial hypertension

BACKGROUND

There is a need for reliable prognostic parameters in pulmonary arterial hypertension (PAH), especially in children. Pulsatile components of the right ventricular afterload, represented by pulmonary arterial compliance (PACi) and pulmonary stroke volume (PSVi), may provide important additional prognostic information to conventional static haemodynamic parameters. The aim of this study was to determine the prognostic value of PACi and PSVi in paediatric PAH.

METHODS

Right heart catheterization data of 52 consecutive paediatric idiopathic/hereditary PAH and PAH associated with congenital heart disease patients with full haemodynamic evaluation seen at the Dutch national referral centre for paediatric pulmonary hypertension between 1993 and 2010 were reviewed. A control group was composed of patients with normal pulmonary vascular resistance. PSVi and PACi were calculated and tested for predictive value for transplant-free survival.

RESULTS

PAH patients had significantly lower PSVi and PACi compared to control patients. PSVi and PACi were lower in patients with higher WHO-functional class compared to those with lower functional classes. Higher PSVi, PACi and mSAP and lower mPAP/mSAP and heart rate were associated with improved survival, independent from WHO-functional class and PAH-targeted therapy. In multivariate analyses PSVi, heart rate and mSAP emerged as the strongest haemodynamic predictors of survival. The effect of vasodilator challenge on the haemodynamic variables did not provide additional prognostic information.

CONCLUSIONS

The parameters of both the pulsatile and static pulmonary circulations are strong independent predictors for transplant-free survival, and therefore can be of complementary value in assessing disease severity, predicting survival and guiding treatment in paediatric PAH.

Reinforcement of dynamically vulcanized EPDM/PP elastomers using organoclay fillers

Dynamically vulcanized EPDM/PP (ethylene-propylene-diene/polypropylene) elastomers reinforced with various amounts of organoclay were prepared using octylphenol-formaldehyde resin and stannous chloride dehydrate as vulcanizing agents. The effects of organoclay on vulcanization characteristics, rheological behavior, morphology, thermal stability and thermomechanical properties were studied. Experimental results showed that organoclay affected neither the vulcanization process nor the degree of vulcanization chemically. X-ray analysis revealed that these organoclay-filled thermoplastic vulcanizates (TPVs) were intercalated. With respect to the mechanical properties, organoclay increased both the strength and degree of elongation of TPVs. The morphological observation of fractured surfaces suggested that organoclay acted as a nucleating agent in TPVs, improving their mechanical properties. However, adding organoclay reduced the thermal stability of TPVs by decomposing the swelling agents in the organoclay.