Whether you plunged down a playground slide as a child or snuck a sip straight from the milk jug when no one was looking, you more than likely did so using low-density polyethylene thermoplastic. Commonly referred to as LDPE, this versatile material makes up one of the most widely used plastics in use today. But with so many polyethylene types crowding the market, it can be a challenge for someone outside of the plastics industry to gauge whether they’re actually using an LDPE product. While there are definitely overlapping characteristics of different polyethylene types, today we put LDPE beneath the magnifying glass to get a better idea of this incredible material.
A Brief History of LDPE
In 1933, Imperial Chemical Industries synthesized LDPE for the first time, marking this as the birth of polyethylene in general. In a case that’s rare for science, ICI has never been challenged to evolve the process of forging LDPE; a system that relies heavily on free radical polymerization. Over the years, LDPE dropped in popularity in the face of the much more versatile high density polyethylene (HDPE) but the polymer remains responsible for generating well over $30 billion annually.
Unique Structural Attributes
The structure of LDPE is unique in that, compared to other polyethylene polymers, it boasts the most molecular branching. Other polymers often adhere to a rather strict, perfectly straight chain of molecules while LDPE is prone to branching its chains in various directions. This structure strongly contributes to the attributes that make LDPE so unique; chiefly the polymer’s lower density, lending to its name.
Benefits of LDPE
Many polyethylene polymers serve as ideal blockades against alcohol and water vapor. LDPE ranks among those materials that put up a strong barrier to vapors, though the polymer has issues when it comes to blocking gases. This actually distinguishes it very little from the majority of closely related polyethylene materials, all noted for similar effectiveness.
A major benefit of LDPE, owing to its branching structure, is the polymer’s flexibility. This attribute has made it a go-to material for plastic packaging as the flexibility allows it to fit to a product’s form easily. However, LDPE would be a poor choice of packaging material for fragile items as this same flexibility does not offer much resistance to mechanical damage. But this doesn’t mean that LDPE itself offers poor impact resistance. On the contrary, the flexible polymer is noted for its strength in the face of impact. However, this simply indicates that the LDPE material itself withstands the impact while the fragile product within may not be so fortunate.
Another reason that demand remains high for LDPE is its ability to resist the corrosive effects of a multitude of agents ranging from acids and greases to basic moisture. If met by such normally corrosive substances, the polymer will maintain its strength instead of releasing potential carcinogens and harmful chemicals.
Negative Traits of LDPE
However, certain traits of LDPE prevent it from being used as an all-purpose plastic. Its structure is such that it can expand under the influence of heat which can render it susceptible to the elements. LDPE can crack under duress, leaving it heavily compromised by stress. In addition, it has more trouble bonding than other polyethylene polymers.
The low cost and structural benefits of LDPE continue to place it in your hands on a daily basis. It’s the preferred polymer for plastic shopping bags, wire insulation, and trash bags. Its resistance to grease, acids, and moisture makes it an ideal choice for food storage containers. Likewise, its flexibility and affordability makes it the perfect material for certain types of plastic packaging. Despite stiff competition from other polymers, LDPE still offers enough unique benefits to continue a strong bid for its lofty niche in the plastic industry.