Hot Compaction Method Research Articles

Facile, green and affordable strategy for structuring natural graphite/polymer composite with efficient electromagnetic interference shielding

The mechanical mixing and hot compaction method was firstly used to fabricate graphite/polymer segregated composite for efficient electromagnetic interference shielding.

Sr-anorthite glass ceramic with enhanced crack resistance, reinforced with silicon nitride particles

It is demonstrated that composite materials based on Sr-anorthite glass ceramic can be synthesized with finely dispersed α-Si3N4 and β-Si3N4 powders introduced as fillers. A study of the influence exerted by the polymorphic forms of fillers, their morphology, dispersity, and concentration and also by the nature of the matrix on the synthesis, structure, and properties of the composites demonstrated that the mechanism and temperature range of sintering in syntheses of materials are determined by the nature of the matrix and the degree of densification and the structure of the composite depend on the concentration, dispersity, and shape of filler particles, their phase composition, and wettability of the glass-phase matrix. In syntheses of glass-crystalline composites by the hot compaction method, raising the filler content from 10 to 70 vol % leads to a substantial decrease in the density of the materials (by 20%); the maximum content of the filler should not exceed 30 vol %. The use of both α-Si3N4 and β-Si3N4 in an amount of 30% made it possible to raise the critical stress intensity coefficient of the strontium-aluminosilicate matrix by more than a factor of 2. A study of the thermal properties of the composites demonstrated that the glass-crystalline matrix can protect nonoxide fillers from oxidation by atmospheric oxygen at elevated temperatures, with the oxidation onset temperature increased by 300°. The developed class of composites is promising for application in airspace technology, chemical industry, and motor-vehicle construction.

Enhanced mechanical properties of polyethylene composites with low content of electrospun nylon-66 nanofibers

High density polyethylene (HDPE) based composites containing electrospun nylon-66 nanofibers were successfully prepared by a hot-compaction method. Incorporation of a low content of nanofibers can simultaneously improve tensile strength, modulus and toughness. The mechanisms for reinforcement and toughening were investigated. The increased crystallinity, accompanied with the fact that HDPE melt impregnates the inter-fiber voids and nanofibers are therefore firmly embedded into the matrix, is responsible for the improved tensile strength and modulus. Moreover, an increase in amorphous thickness with the increasing nanofiber content mainly contributes to the enhanced toughness.

Mechanical properties of self-reinforced poly(lactic acid) composites prepared by compression moulding of non-woven precursors

A hot compaction method has been used to form all-PLA composites by partial melting and fusion of fibres in non-woven mats where the matrix phase is formed from partially melted fibres and the reinforcement phase is the original PLA fibres that remain. Compaction required a minimum of 10 min heating at temperature range 172°C to 176°C under a load of 2.4 MPa. An advantage is that the oriented high tensile strength fibre properties are retained, while matrix adhesion is strong because melt adhesion is provided by the same polymer. The all-PLA composite structure was confirmed using scanning electron microscopy (SEM) and wide-angle X-ray scattering. Mechanical properties were evaluated from modulated force thermo-mechanical analysis. The temperature window below melting temperature of PLA of about at 172°C to 176°C was found as the optimum temperature for all-PLA composites with optimum properties. SEM study also shown the gaps between the fibers are filled with recrystallised material that has melted from the original fibres.

Apatite wollastonite–poly methyl methacrylate bio-composites

Bio-composites consisting of sol–gel processed apatite wollastonite (AW) glass ceramics and poly methyl methacrylate (PMMA) were prepared by hot compaction method. Density of the composites decreased with increase in PMMA content, while, biaxial flexural strength (BFS) was 21 MPa for 20 wt.% PMMA and beyond which it decreased. A correlation between phase compositions of AW glass ceramics with BFS was attempted from the XRD results. In vitro bioactivity of the composites in a simulated body fluid (SBF) showed the formation of spherical globules on the surface within 7 days of soaking as observed by environmental SEM. Thin film XRD and EDX measurement confirmed these globules to be bone like apatite with Ca/P ratio 1.53 and FTIR measurement showed the corresponding peaks for phosphates. Results indicated the bone bonding ability of the composites by forming a surface apatite (calcium phosphate) layer in SBF and the growth increased with increase in soaking durations. ICP measurement of the remaining SBF after 7, 14 and 21 days soaking of samples was found to be in good agreement with the EDX analysis results.

Temperature dependence of electrical resistivity for carbon black filled ultra-high molecular weight polyethylene composites prepared by hot compaction

In this article, the temperature dependence of electrical resistivity is studied for carbon black (CB)/ultra-high molecular weight polyethylene (UHMWPE) composites. A new positive temperature coefficient (PTC) material with a very low percolation threshold is produced by the hot compaction method. The very low percolation threshold can be attributed to the segregation of CB in the interfacial regions of UHMWPE particles. The percolation threshold decreases with the increase of the molecular weight of UHMWPE, and with the decrease of the particle size of CB. For CB filled lower molecular weight UHMWPE (145M) composites, the PTC temperature, at which a sharp increase in the resistivity of the composite occurs, decreases with the increase of CB size. However, for a higher molecular weight UHMWPE (630M) filled with CB, the second PTC effect is observed and the negative temperature coefficient (NTC) effect is eliminated. A mechanism is proposed to explain these phenomena based on the optical microscopy and TEM observations. It can be concluded that the degree of the intermixing between CB and UHMWPE particles plays an important role in determining the electrical properties of the composites.

The effect of processing temperature and time on the structure and fracture characteristics of self-reinforced composite poly(methyl methacrylate).

A novel material, self-reinforced composite poly(methyl methacrylate) (SRC-PMMA) has been previously developed in this laboratory. It consists of high-strength PMMA fibers embedded in a matrix of PMMA derived from the fibers. As a composite material, uniaxial SRC-PMMA has been shown to have greatly improved flexural, tensile, fracture toughness and fatigue properties when compared to unreinforced PMMA. Previous work examined one empirically defined processing condition. This work systematically examines the effect of processing time and temperature on the thermal properties, fracture toughness and fracture morphology of SRC-PMMA produced by a hot compaction method. Differential scanning calorimetry (DSC) shows that composites containing high amounts of retained molecular orientation exhibit both endothermic and exothermic peaks which depend on processing times and temperatures. An exothermic release of energy just above Tg is related to the release of retained molecular orientation in the composites. This release of energy decreases linearly with increasing processing temperature or time for the range investigated. Fracture toughness results show a maximum fracture toughness of 3.18 MPa m1/2 for samples processed for 65 min at 128 degrees C. Optimal structure and fracture toughness are obtained in composites which have maximum interfiber bonding and minimal loss of molecular orientation. Composite fracture mechanisms are highly dependent on processing. Low processing times and temperatures result in more interfiber/matrix fracture, while higher processing times and temperatures result in higher ductility and more transfiber fracture. Excessive processing times result in brittle failure.