Are Woven Polypropylene Bags Waterproof?
Are Woven Polypropylene Bags Waterproof?
Are pp woven bags waterproof? As far as the
woven bag itself is
concerned, because the woven bag is made of warp and weft tapes, there is only overlap between the tapes, which does not have
sealing property. Therefore, the liquid will be left through the gap between the tapes, so the woven bag itself is not
waterproof.
However, due to the special requirements of chemical industry, cement, chemical fertilizer, sugar and other industries for
packaging, a considerable number of plastic woven bags must have the function of waterproof and sealing. At present, there
are mainly two types of waterproof and sealed woven bags produced and applied in the market: one is the ordinary separate
combined packaging bag with outer woven bag and inside liner inserted or stitched bag. The other is the composite woven bag
coated with a layer of plastic film on the PP woven cloth, which will include two types also, either polypropylene coated
woven bag or pp woven laminated bag.
The production equipment and process of the first kind of separated inner lining membrane woven bag are relatively simple,
the equipment investment is low, and the application is very wide. The inner and outer bags are separated. The inner bag is
blown film bag, which can be divided into LDPE and HDPE. The outer bag is ordinary PP woven bag, and the length and width of
the inner bag are slightly larger than the outer bag. When loading materials, the inner and outer bags are uneven and easy to
be damaged. In the early years, the inner and outer bags of the inner lining membrane bag and the outer bag need to be set
together manually, and the inner and outer bags at the mouth of the bag need to be aligned and sewed, so the production
efficiency is low, the waste of manpower is large, and the continuous and efficient production cannot be carried out. A
skilled operator can only complete about 1000 bags by hand every day, and only about 300 bags can be sewn by hinge sewing
machine every day. Nowadays, with the improvement of all-in-one machine, there are many machinery manufacturers in China that
can produce all-in-one machines for bag cutting, sewing and lining. The technology has been widely used and tends to be
mature, greatly improving the production efficiency.
Another kind of Coated plastic woven
bag production must go through the coating
process, using the extrusion coating machine to coat a layer of plastic film with a thickness of about 0.02 ~ 0.04mm on the
outside of the woven pp cloth. Or at the same time, to use the coating material as the bonding medium, and then composite a
layer of BOPP film on the surface, can achieve better waterproof effect, it was named BOPP pp woven laminated bag. When doing
coating, the temperature of the extruded film is about 300 ℃, and the newly extruded film is combined with the braid by a
pair of cooling rollers. However, such high temperature reduces the strength of the cloth surface, reduces the elasticity,
increases the brittleness of the bag surface, and makes the bag easier to be damaged in the falling tests.
WHAT IS ARE VALVE BAGS?
Valve bags are packaging bags filled by machines. They come in plastic or paper. Here at Western Packaging, we are a
wholesale manufacturer who offers the paper version, with many options. The three main things to consider are size, closure
type, and coatings.
CHOOSE THE RIGHT SIZE
Paper valve bags come in a large range of sizes. We offer small to very large paper valve bags and multiple sizes in
between. It is important to verify which sizes your
valve bag machine
handles.
DETERMINE WHICH TYPE OF CLOSURE YOU NEED
Once the size is determined, the type of closure is determined. All valve bags are automatically closed. The specific
method of how this closing happens falls into three categories.
1. SELF- SEALING
The first and most common is self-sealing. These valve bags use the pressure of the contents to close and seal the bag.
2. HEAT SEALED
Alternatively, some bags can be sealed by heat. This may be a better option for the product and requires a machine and
set up capable of this method.
3. ULTRASONIC SEALS
The third type of closure is much less common. Bags can be sealed ultrasonically. These valve bags are only used in very
specific and limited industries. They require clean and sterile environments and very special machinery.
WHICH COATING IS BEST
Once the size and type of closure are decided, coatings in and on the bags is decided. The options are extensive. Western
Packaging offers all the most common, and some uncommon, coatings available. The specific coating(s) depends on the product
and the package’s method of storage, shipment, and display.
There is a large variety of coatings available. The coating options vary based on if the coating is going to be placed on
the inside or outside of the bag. Some products may benefit from a coating on both.
THE DIFFERENCE BETWEEN INSIDE COATS
The inside coating is most important when the product contained in the bag is food or non-food products. In these
situations, a food-safe coating must be applied to the inside of the bag. This coating helps ensure the contents remain safe
for consumption, and also maintains the freshness. Interior coatings also help minimize moisture entering the product and/or
keep the product from seeping out. These are very important features for many products.
Some outside coatings provide the same or similar benefits. Coatings can be applied to block moisture, block
contamination of the interior from the outside, or make the bag easier to handle. While protection of the contents of the
packaging is most important, ease of storage is also important. Outside coatings can be used to minimize friction when bags
rub together and therefore help to minimize bag damage and loss of product. A simple coating can also help the filled bag
maintain its shape.
THE BENEFITS OF VALVE BAGS
Valve bagging is when a bag is filled using a specialized machine. The machine uses a spout placed in or near the opening
of the bag. A measured amount is placed in each bag. This can be done in a fully automated or semi-automated manner. This
ensures consistency in quantity and minimizes lost product.
The benefits of these machines are numerous and span multiple industries. The biggest benefit is the volume of bags that
can be filled and closed per hour. The output is significantly higher than if done by an employee. This increase in output
translates to higher profit by filling orders more quickly. Businesses converting to this method often find the cost of the
machine is quickly covered and a return on investment is recognized very soon.
Plastic, Paper or Cotton: Which Shopping Bag is Best?
Plastic bags
Plastic bags were invented in 1967, but only became widely used in stores in the 1970s. The most commonly found thin
plastic
shopping bag given out at cash registers are usually made of
high-density polyethylene (HDPE), but some are made of low-density polyethylene plastic (LDPE).
The energy embodied in plastic bags comes initially from the mining of the raw materials needed to make them—natural gas
and petroleum—whose extraction requires a lot of energy. The raw materials must then be refined, which requires yet more
energy. Once at a processing facility, the raw materials are treated and undergo polymerization to create the building blocks
of plastic. These tiny granules of polyethylene resin can be mixed with recycled polyethylene chips. They are then
transported by truck, train or ship to facilities where, under high heat, an extruder shapes the plastic into a thin film.
The film is flattened, then cut into pieces. Next, it is sent to manufacturers to be made into bags. The plastic bags are
then packaged and transported around the world to vendors. While polyethylene can be reprocessed and used to make new plastic
bags, most plastic bags are only used once or twice before they end up being incinerated or discarded in landfills. The Wall
Street Journal estimated that Americans use and dispose of 100 billion plastic bags each year; and the EPA found that less
than five percent are recycled.
A 2014 study done for the Progressive Bag Alliance, which represents the U.S. plastic bag manufacturing and recycling
industry, compared grocery bags made from polyethylene (HDPE), compostable plastic, and paper with 30 percent recycled
fibers. It found that the HDPE bags ultimately used less fuel and water, and produced less greenhouse gas gases, acid rain
emissions, and solid waste than the other two. The study, which did not consider litter, was peer-reviewed by Michael
Overcash, then a professor of chemical engineering at North Carolina State University. Because the carrying capacity of a
plastic and a paper bag are not the same, the study used the carrying capacity of 1,000 paper bags as its baseline and
compared their impacts to the impacts of 1,500 plastic bags. The plastic bags used 14.9kg of fossil fuels for manufacturing
compared to 23.2kg for paper bags. Plastic bags produced 7kg of municipal solid waste compared to 33.9kg for paper, and
greenhouse gas emissions were equivalent to 0.04 tons of CO2 compared to paper’s 0.08 tons. Plastic bags used 58 gallons of
fresh water, while paper used 1,004 gallons. Energy use totaled 763 megajoules for plastic, and 2,622 megajoules for paper.
Sulfur dioxide, a type of sulfur oxide, and nitrogen oxide emitted from coal-fired power plants that produce the energy
for processing bags contribute to acid rain. The plastic bag produced 50.5 grams of sulfur oxides compared to 579 grams for
the paper bag; and 45.4 grams of nitrogen oxides, compared to 264 grams for paper.
A 2011 U.K. study compared bags made of HDPE, LDPE, non-woven polypropylene, a biopolymer made from a starch polyester,
paper and cotton. It assessed the impacts in nine categories: global warming potential, depletion of resources such as fossil
fuels, acidification, eutrophication, human toxicity, fresh water toxicity, marine toxicity, terrestrial toxicity and smog
creation. It found that HDPE bags had the lowest environmental impacts of the lightweight bags in eight of the nine
categories because it was the lightest bag of the group.
Paper bags
Paper bags are made from a renewable resource and are biodegradable. In the U.S., over 10 billion paper bags are consumed
each year, requiring the felling of 14 million trees.
Once the trees are cut down, the logs are moved to a mill where they can wait up to three years until they dry out. Once
ready, bark is stripped off and the wood is chipped into one-inch cubes that are subjected to high heat and pressure. They
are then mixed with limestone and sulfurous acid until the combination becomes pulp. The pulp is washed with fresh water and
bleach then pressed into paper, which is cut, printed, packaged and shipped. As a result of the heavy use of toxic chemicals
in the process, paper is responsible for 70 times more air pollution and 50 times more water pollution than
plastic bag production according to a Washington Post analysis, resulting
in more toxicity to humans and the environment than HDPE bags. And while 66 percent of paper and paperboard are recycled, the
recycling process requires additional chemicals to remove the ink and return the paper to pulp, which can add to paper’s
environmental impact.
Cotton totes
Cotton bags are made from a renewable resource and are biodegradable. They are also strong and durable so they can be
reused multiple times.
Cotton first needs to be harvested, then cotton bolls go through the ginning process, which separates the cotton from
stems and leaves. Only 33 percent of the harvested cotton is usable. The cotton is then baled and shipped to cotton mills to
be fluffed up, cleaned, flattened and spun. The cotton threads are woven into fabric, which then undergoes a chemical washing
process and bleaching, after which it can also be dyed and printed. Spinning, weaving and other manufacturing processes are
energy intensive. Washing, bleaching, dyeing, printing and other processes use large amounts of water and electricity.