Today's KNOWLEDGE Share:Overmolding Metal Insert

Today's KNOWLEDGE Share

Overmolding a metal insert often poses specific molding challenges due to shrinkage disparities, primarily stemming from differences in coefficient of thermal expansion (CTE) between materials. This incongruity leads to elevated residual stresses after ejection, contributing to subsequent warpage.

To alleviate warpage, it is crucial to optimize the alignment of metal and polymer expansion coefficients.

For instance, pairing magnesium with 50% glass-filled nylon can significantly reduce warpage by closely matching their CTEs, outperforming the alternative of overmolding stainless steel with unfilled PA66.

Furthermore, optimizing the gating solution proves advantageous in producing lower warpage overmolded plastic/metal parts, due to the typical anisotropic shrinkage of glass-filled grades.

The parallel to flow direction better matches the metal near-zero shrinkage.

Increasing packing pressure proportionally diminishes the shrinkage anisotropy of glass-filled polymer and concurrently reduces overall average shrinkage, thereby minimizing discrepancies with the insert. In simple terms, the higher the packing, the less prone this overmolded bi-material part is to warping.

Preheating and/or pre-stretching the metal insert prior to molding the polymer can also do miracles for warpage !

source:Vito leo

Today's KNOWLEDGE share: PET Vs PETG

Today's KNOWLEDGE share:

PET Vs PETG: THE MAIN DIFFERENCES

A basic formula for making polyesters, like PET and PETG, is the combination of acid monomers plus glycol monomers. In the case of PET, the acid is usually DMT (dimethyl terephthalate) and the glycol is ethylene glycol. These two monomers are the building blocks of the final long-chain polymer: polyethylene

terephthalate.

For creating PETG, the same monomers are used, except some ethylene glycol (30-60%) is substituted with a different glycol monomer, CHDM (cyclohexanedimethanol). So it’s not that PETG has significantly more or less glycol than PET, it just has a different type of glycol. Therefore, the -G in PETG represents the chemical modification of the typical PET structure with CHDM glycol units, or “glycol-modified” for short.

The key impact of this glycol modification from a physical standpoint is that semi-crystalline PET gets transformed into amorphous PETG. Let’s quickly review what crystallinity has to do with polymers and why its relevant to 3D printing.

In a few words, amorphous polymers have all their chains arranged randomly, much like a bowl of spaghetti. Semi-crystalline polymers contain regions of crystallinity where chains are highly-ordered and densely packed. This has an enormous impact on material properties.

Semi-crystalline materials are generally more rigid compared to a totally amorphous counterpart, as crystalline regions can function as reinforcement. This holds true for semi-crystalline PET and amorphous PETG.

While cooling, semi-crystalline materials are prone to warping caused by changes in density brought on by the formation of crystalline regions. This means amorphous PETG is much more manageable for 3D printing. Semi-crystalline PET, on the other hand, requires stricter printing and ambient temperatures to prevent distortions.

PET also has a slightly higher working temperature compared to PETG due to its crystalline nature. While this may make it more difficult to print with, PET will hold up better in applications that require some thermal resistance.

You may also notice visual differences between the two materials. The purely random nature of the polymer chains in PETG creates glossy or even transparent filaments. PET, as a mixture of crystalline and non-crystalline regions, will have some haziness.

Crystalline structures, like those of PET, don’t play well with extrusion. Crystallization is difficult to control and can begin as soon as the plastic is just a bit too cool. Manufacturers often facilitate extrusion using additives that hinder crystallization.

On the other hand, glycol modification of PET renders it an amorphous material that can easily be modeled via extrusion, injection molding, and other thermo-forming processes. This is the key to the success of PETG.

Source:all3dp

#3dprinting #plastics #pet #petg #molding

Today's KNOWLEDGE Share:Types of Fibers

Today's KNOWLEDGE Share

Composite Essentials!

What are some of the different fiber types that can be used as reinforcement phases in composite materials? 

Today we would like to share with you the definitions and examples of the most common fibers used in the industry! 

Carbon fibers are long and thin strands of material with about 0.005-0.010 mm in diameter, composed mostly of carbon atoms (more than 90% content). The carbon atoms are bonded together in microscopic crystals that are more or less aligned parallel to the long axis of the fiber. The crystal alignment makes the fiber incredibly strong for its size. 

Glass fiber is a non-metallic material made from extremely fine fibers of glass. The base ingredients of glass fibers are forms of silica, mainly sand, limestone, stone ash and borax. It is also considered the oldest, and most familiar, performance fiber. 

Aramid (short for “aromatic polyamide”) fibers are synthetic fibers in which the fiber-forming substance is a long-chain synthetic polyamide that has at least 85% of the amide linkages attached directly to two aromatic rings. Its molecules are linked by strong hydrogen bonds that transfer mechanical stress very efficiently, making it possible to use chains of relatively low molecular weight. The most famous aramid fiber is DuPont's Kevlar. 

Polymer fibers are a subset of artificial fibers, which are based on synthetic chemicals rather than arising from natural materials by a purely physical process. Examples: PE fibers (Dyneema, Spectra), PP fibers (Innegra), PET fibers, polyester fibers and many others. Aramid fibers are also considered polymeric. 

Natural fibers are fibers that are produced by geological processes, or from the bodies of plants or animals. Examples: Hemp, jute, flax, kenaf, basalt, cotton, etc. 

Other fibers that we can mention: Boron fibers, metallic fibers (aluminum, titanium, steel) and ceramic oxide fibers. 

Now imagine the amount of possibilities when it comes to creating hybrid fabrics! 

source:managingcomposites/thenativelab

Today's KNOWLEDGE Share:Mycelium Composites

Today's KNOWLEDGE Share

Mushroom-derived materials could offer benefits for developing nations in Africa

A research team from the University of Bristol has suggested that mycelium composites could offer a sustainable alternative to traditional building materials and help address socio-economic and environmental challenges in Africa.

Mycelium composites are a class of materials based on mycelium – the roots of mushrooms. These versatile materials, which have gained popularity in Europe and the US in the past decade, are produced by harnessing the ability of fungi to grow by feeding on organic biomass – eliminating the need for high-end manufacturing processes. In fact, mycelium composites can be grown almost anywhere – even at home – without the need for extensive expertise or advanced equipment.

The organic biomass used for the basis of mycelium composites are often obtained from agricultural, agro-industrial, and forestry waste streams. There is a wide range of applications for mycelium composites, including packaging materials, insulation panels, floor tiles, and furniture.

Mycelium composites are also envisioned as the ‘next-generation of self-healing and self-growing’ structures in construction. This can be achieved due to the ability of fungi to respond to light, chemicals, gases, gravity, electric fields, and mechanical cues.

Stefania’s paper suggests mycelium composites can add value to agricultural waste, potentially offering an incentive for investment in the agricultural sector and increasing productivity. Mycelium composite production could also serve as a greener waste management route not only for agricultural waste, but for plastics and other carbon-based waste materials too.

The next step for the authors is to fine-tune the properties and production of mycelium composites in order to facilitate the integration of this technology with well-established practices in diverse developing countries.

source:bristol.ac.uk/jeccomposites

Single proton illuminates perovskite nanocrystals-based transmissive thin scintillators

National University of Singapore (NUS) researchers have developed a transmissive thin scintillator using perovskite nanocrystals, designed for real-time tracking and counting of single protons. The exceptional sensitivity is attributed to biexcitonic radiative emission generated through proton-induced upconversion and impact ionisation.

The detection of energetic particles plays an important role in advancing science and technology in various fields, ranging from fundamental physics to quantum technology, deep space exploration and proton cancer therapy. The increasing demand for precise dose control in proton therapy has fuelled extensive research into proton detectors. One promising approach to enable proton counting during radiotherapy involves the development of high-performance thin-film detectors that are transmissive to protons.

Despite advancements in silicon-based, chemical vapour deposition, diamond-based, and other types of proton detectors in recent years, a fundamental challenge remains unresolved: achieving real-time proton irradiation with single-proton counting accuracy. In single-proton detection, the detectable signal is fundamentally limited by the thickness of the detector. Therefore, a proton-transmissive detector must be fabricated at an ultrathin thickness while retaining sensitivity for single-proton detection. Existing particle detectors, such as ionisation chambers, silicon-based detectors and single-crystal scintillators, are too bulky to allow the transmission of protons. Additionally, organic plastic scintillators suffer from low scintillation yields and low particle radiation tolerances due to their low electron density, which hampers their single-proton detection sensitivity.

A research team led by Professor LIU Xiaogang from the Department of Chemistry and Associate Professor Andrew BETTIOL from the Department of Physics, NUS demonstrated the real-time detection and counting of single protons using thin-film transmissive scintillators made of CsPbBr3 nanocrystals. This approach offers unparalleled sensitivity with a light yield approximately double that of commercially available BC-400 plastic thin-film scintillators and ten times greater than conventional bulk scintillators such as LYSO:Ce, BGO and YAG:Ce crystals.

Their findings have been published in the journal Nature Materials.

The thin-film nanocrystal scintillators, with a thickness of approximately 5 µm, exhibit high sensitivity that allows for a detection limit of 7 protons per second. This sensitivity is about five orders of magnitude lower than clinically relevant counting rates, making it a significant advancement in single-proton detection technology.

source:The Graphene Council

Arkema Expands its Global Production Capacity for Elastomers by 40%

Arkema has increased its global manufacturing capacity for Pebax® elastomers by 40% at its Serquigny plant in France. This expansion supports its customers’ strong growth, in particular in the sports and consumer goods markets.

Used in Sports Equipments, Electronic and Medical Devices:

Arkema has started its new Pebax® elastomer unit at the Serquigny plant in France. This new unit is designed with the latest advancements in industrial processes. It can produce both the bio-circular Pebax® Rnew® and classical Pebax® elastomer ranges.

These advanced materials are used in sports equipment such as running shoes, soccer shoes and ski boots. Other uses are in electronic devices, and specialty markets such as antistatic additives and medical devices.

"We are excited to start the production of this expansion in our Pebax® elastomers capacity. This represents a great opportunity for us to meet growing demand in existing and new applications while simultaneously improving our processes as water consumption at the site will be reduced by approximately 25%," said Erwoan Pezron, senior vice-president of Arkema's High Performance Polymers Business Line.

Source: Arkema/omnexus.spcialchem

TotalEnergies Produces Circular Polymers by Recycling Feedstocks from Plastic Waste

TotalEnergies converts feedstocks from plastic waste into circular polymers at its polypropylene plant in La Porte, Texas.

The La Porte plant is one of the world's largest polypropylene sites. It will produce sustainably certified polymers. These polymers will be suitable for a wide range of applications, including food grade packaging.

Patented Pyrolysis Technology Processes Mixed Plastic Waste

The petrochemical feedstock was provided by New Hope Energy's ISCC+ certified advanced recycling facility in Tyler, Texas. The feedstock was converted into monomers at the BASF TotalEnergies Petrochemicals (BTP) facility. It is a 60/40 joint venture between BASF and TotalEnergies. BTP facility is based in Port Arthur, Texas. The monomers were then transformed into circular polymers at TotalEnergies' plant in La Porte, Texas. Both the La Porte and BTP facilities received their ISCC+ certification in 2022.

TotalEnergies and New Hope Energy have also signed a multi-year agreement. Under this agreement, New Hope Energy will supply TotalEnergies with petrochemical feedstock made from plastics to produce recycled polymers. New Hope Energy uses a patented pyrolysis technology developed in partnership with Lummus Technology. It processes and converts mixed plastic waste that would otherwise end up in landfill or incineration.

"After Europe, this first production of circular polymers from advanced recycling in the United States is a new step forward in our commitment to meeting the global market's growing demand for more innovative and sustainable plastics, as well as in our ambition to produce one million tons of circular polymers a year by 2030," said Heather Tomas, vice president Polymers Americas.

"We are excited to partner with TotalEnergies in our mutual effort to transform plastic for a cleaner world," said Rusty Combs, chief executive officer of New Hope Energy. "This supply agreement is an important step towards achieving New Hope's goal of creating pyrolysis projects at a scale that will materially improve the nation's plastic recycling performance. We are honored by the confidence TotalEnergies has placed in both our team and our robust technology."

Source: TotalEnergies/omnexus.specialchem